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  Subjects -> PHYSICS (Total: 784 journals)
    - ELECTRICITY AND MAGNETISM (9 journals)
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    - NUCLEAR PHYSICS (48 journals)
    - OPTICS (90 journals)
    - PHYSICS (569 journals)
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PHYSICS (569 journals)            First | 1 2 3 4 5 6 | Last

New Journal of Physics     Open Access   (Followers: 7)
Niels Bohr Collected Works     Full-text available via subscription  
Noise & Vibration Worldwide     Full-text available via subscription   (Followers: 5)
Noise Notes     Full-text available via subscription   (Followers: 3)
Nondestructive Testing And Evaluation     Hybrid Journal   (Followers: 8)
Nonlinear Dynamics     Hybrid Journal   (Followers: 5)
NTM Zeitschrift für Geschichte der Wissenschaften, Technik und Medizin     Hybrid Journal   (Followers: 4)
Nuclear Engineering and Design     Hybrid Journal   (Followers: 12)
Nuclear Medicine and Biology     Hybrid Journal   (Followers: 1)
Nuclear Receptor     Full-text available via subscription   (Followers: 1)
Open Journal of Biophysics     Open Access   (Followers: 1)
Open Journal of Fluid Dynamics     Open Access   (Followers: 3)
Open Journal of Microphysics     Open Access  
Optical Communications and Networking, IEEE/OSA Journal of     Hybrid Journal   (Followers: 5)
Optofluidics, Microfluidics and Nanofluidics     Open Access   (Followers: 1)
Organic Electronics     Hybrid Journal   (Followers: 4)
Organic Photonics and Photovoltaics     Open Access   (Followers: 2)
PAJ: A Journal of Performance and Art     Hybrid Journal   (Followers: 12)
Papers in Physics     Open Access  
Particle Physics Insights     Open Access   (Followers: 2)
Particuology     Hybrid Journal  
Pattern Recognition in Physics     Open Access   (Followers: 2)
Pergamon Materials Series     Full-text available via subscription  
Phase Transitions and Critical Phenomena     Full-text available via subscription   (Followers: 1)
Philosophical Magazine     Hybrid Journal   (Followers: 2)
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences     Full-text available via subscription   (Followers: 6)
Philosophy and Foundations of Physics     Full-text available via subscription  
Physica B: Condensed Matter     Hybrid Journal   (Followers: 6)
physica status solidi (a)     Hybrid Journal   (Followers: 1)
physica status solidi (b)     Hybrid Journal   (Followers: 1)
physica status solidi (c)     Hybrid Journal   (Followers: 1)
Physica Status Solidi - Rapid Research Letters     Hybrid Journal   (Followers: 1)
Physical Communication     Hybrid Journal   (Followers: 2)
Physical Review C     Full-text available via subscription   (Followers: 18)
Physical Review Special Topics - Physics Education Research     Open Access   (Followers: 6)
Physical Review X     Open Access   (Followers: 6)
Physical Sciences Data     Full-text available via subscription   (Followers: 1)
Physics - spotlighting exceptional research     Full-text available via subscription   (Followers: 1)
Physics and Chemistry of Glasses - European Journal of Glass Science and Technology Part B     Full-text available via subscription   (Followers: 2)
Physics and Chemistry of Liquids: An International Journal     Hybrid Journal   (Followers: 2)
Physics and Chemistry of the Earth, Parts A/B/C     Hybrid Journal   (Followers: 3)
Physics and Materials Chemistry     Open Access  
Physics Essays     Full-text available via subscription  
Physics in Medicine & Biology     Full-text available via subscription   (Followers: 10)
Physics in Perspective     Hybrid Journal   (Followers: 1)
Physics International     Open Access   (Followers: 2)
Physics Letters A     Hybrid Journal   (Followers: 9)
Physics Letters B     Open Access   (Followers: 3)
Physics of Fluids     Hybrid Journal   (Followers: 24)
Physics of Life Reviews     Hybrid Journal   (Followers: 1)
Physics of Plasmas     Hybrid Journal   (Followers: 6)
Physics of the Dark Universe     Open Access  
Physics of the Solid State     Hybrid Journal   (Followers: 3)
Physics of Wave Phenomena     Hybrid Journal   (Followers: 1)
Physics Procedia     Partially Free   (Followers: 1)
Physics Reports     Full-text available via subscription   (Followers: 2)
Physics Research International     Open Access   (Followers: 1)
Physics Today     Hybrid Journal   (Followers: 34)
Physics World     Full-text available via subscription   (Followers: 3)
Physics-Uspekhi     Full-text available via subscription  
Physik in unserer Zeit     Hybrid Journal   (Followers: 1)
Physik Journal     Hybrid Journal  
Plasma Physics and Controlled Fusion     Hybrid Journal   (Followers: 3)
Plasma Physics Reports     Hybrid Journal   (Followers: 2)
Pramana     Open Access   (Followers: 9)
Preview     Hybrid Journal  
Proceedings of the National Academy of Sciences     Full-text available via subscription   (Followers: 444)
Proceedings of the National Academy of Sciences, India Section A     Hybrid Journal   (Followers: 3)
Progress in Materials Science     Hybrid Journal   (Followers: 21)
Progress in Planning     Hybrid Journal   (Followers: 1)
Progress of Theoretical and Experimental Physics     Open Access  
Quantum Electronics     Full-text available via subscription   (Followers: 3)
Quantum Measurements and Quantum Metrology     Open Access  
Quantum Studies : Mathematics and Foundations     Hybrid Journal   (Followers: 1)
Quarterly Journal of Mechanics and Applied Mathematics     Hybrid Journal   (Followers: 3)
Radiation Effects and Defects in Solids     Hybrid Journal   (Followers: 1)
Radiation Measurements     Hybrid Journal   (Followers: 2)
Radiation Physics and Chemistry     Hybrid Journal   (Followers: 1)
Radiation Protection Dosimetry     Hybrid Journal   (Followers: 2)
Radiation Research     Full-text available via subscription   (Followers: 3)
Radio Science     Full-text available via subscription   (Followers: 3)
Radiological Physics and Technology     Hybrid Journal   (Followers: 1)
Reflets de la physique     Full-text available via subscription  
Reports on Mathematical Physics     Full-text available via subscription  
Reports on Progress in Physics     Full-text available via subscription   (Followers: 2)
Research & Reviews : Journal of Physics     Full-text available via subscription  
Research in Drama Education     Hybrid Journal   (Followers: 12)
Research Journal of Physics     Open Access  
Results in Physics     Open Access   (Followers: 1)
Reviews in Mathematical Physics     Hybrid Journal  
Reviews of Accelerator Science and Technology     Hybrid Journal  
Reviews of Geophysics     Full-text available via subscription   (Followers: 20)
Reviews of Modern Physics     Full-text available via subscription   (Followers: 17)
Revista Boliviana de Física     Open Access  
Revista Colombiana de Física     Open Access  
Revista Mexicana de Astronomía y Astrofísica     Open Access  
Revista Mexicana de Física     Open Access  
Revista mexicana de física E     Open Access  
Rheologica Acta     Hybrid Journal   (Followers: 3)
Russian Journal of Mathematical Physics     Hybrid Journal  

  First | 1 2 3 4 5 6 | Last

Journal Cover   physica status solidi (c)
  [SJR: 0.471]   [H-I: 31]   [1 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1862-6351 - ISSN (Online) 1610-1642
   Published by John Wiley and Sons Homepage  [1607 journals]
  • Chemical vapor deposition and analysis of thermally insulating ZrO2 layers
           on injection molds
    • Authors: Burak Atakan; Victoria Khlopyanova, Simon Mausberg, Frank Mumme, Adrian Kandzia, Christian Pflitsch
      Abstract: High quality injection molding requires a precise control of cooling rates. Thermal barrier coating (TBC) of zirconia with a thickness of 20‐40 µm on polished stainless steel molds could provide the necessary insulating effect. This paper presents results of zirconia deposition on stainless steel substrates using chemical vapor deposition (CVD) aiming to provide the process parameters for the deposition of uniform zirconia films with such a thickness. The deposition was performed with zirconium (IV) acetylacetonate (Zr(C5H7O2)4) as precursor and synthetic air as co‐reactant, which allows deposition at temperatures below 600 °C. The experiments were carried out in a hot‐wall reactor at pressures between 7.5 mbar and 500 mbar and in a temperature range from 450 °C to 600 °C. Important growth parameters were characterized and growth rates between 1 and 2.5 µm/h were achieved. Thick and well adhering zirconia layers of 38 µm could be produced on steel within 40 h. The transient heat transfer rate upon contact with a hot surface was also evaluated experimentally with the thickest coatings. These exhibit a good TBC performance. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-19T05:30:13.425646-05:
      DOI: 10.1002/pssc.201510033
       
  • Investigation of structural, morphological and electrical properties of
           APCVD vanadium oxide thin films
    • Authors: Georgios Papadimitropoulos; Ioannis Kostis, Stelios Trantalidis, Athanasios Tsiatouras, Maria Vasilopoulou, Dimitris Davazoglou
      Abstract: Vanadium oxide films were chemically vapor deposited (CVD) on oxidized Si substrates covered with CVD tungsten (W) thin films and on glass substrates covered with indium tin oxide (ITO) films, using vanadium(V) oxy‐tri‐isopropoxide (C9H21O4V) vapors. X‐ray diffraction (XRD) measurements showed that the deposited films were composed of a mixture of vanadium oxides; the composition was determined mainly by the deposition temperature and less by the precursor temperature. At temperatures up to 450 °C the films were mostly composed by monoclinic VO2. Other peaks corresponding to various vanadium oxides were also observed. X‐ray microanalysis confirmed the composition of the films. The surface morphology was studied with atomic force microscopy (AFM) and scanning electron microscopy (SEM). These measurements revealed that the morphology strongly depends on the used substrate and the deposition conditions. The well‐known metal‐insulator transition was observed near 75 °C for films mostly composed by monoclinic VO2. Films deposited at 450 °C exhibited two transitions one near 50 °C and the other near 60 °C possibly related to the presence of other vanadium phases or of important stresses in them. Finally, the vanadium oxide thin films exhibited significant sensory capabilities decreasing their resistance in the presence of hydrogen gas with response times in the order of a few seconds and working temperature at 40 °C. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-19T05:30:12.049143-05:
      DOI: 10.1002/pssc.201510029
       
  • Growth mechanism of planar or nanorod structured tungsten oxide thin films
           deposited via aerosol assisted chemical vapour deposition (AACVD)
    • Authors: Min Ling; Chris Blackman
      Abstract: Aerosol assisted chemical vapour deposition (AACVD) is used to deposit tungsten oxide thin films from tungsten hexacarbonyl (W(CO)6) at 339 to 358 °C on quartz substrate. The morphologies of as‐deposited thin films, which are comprised of two phases (W25O73 and W17O47), vary from planar to nanorod (NR) structures as the distance from the inlet towards the outlet of the reactor is traversed. This is related to variation of the actual temperature on the substrate surface (ΔT = 19 °C), which result in a change in growth mode due to competition between growth rate (perpendicular to substrate) and nucleation rate (parallel to substrate). When the ratio of perpendicular growth rate to growth rate contributed by nucleation is higher than 7.1, the as‐deposited tungsten oxide thin film forms as NR. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-13T04:40:11.242767-05:
      DOI: 10.1002/pssc.201510047
       
  • Intermolecular interaction between rare earth and manganese precursors in
           metalorganic chemical vapor deposition of perovskite manganite films
    • Authors: Toshihiro Nakamura
      Abstract: The gas‐phase reaction mechanism was investigated in liquid delivery metalorganic chemical vapor deposition (MOCVD) of praseodymium and lanthanum manganite films. We studied the gas‐phase behavior of praseodymium, lanthanum, and manganese precursors under actual CVD conditions by in situ infrared absorption spectroscopy. The rate of the decrease of the infrared absorbance due to Pr(DPM)3 was almost constant even if Mn(DPM)3 was added, indicating that the intermolecular interaction between Pr and Mn precursors in the gas phase is relatively weak in MOCVD of praseodymium manganite films. On the other hand, the temperature dependence of the infrared absorption indicates that the thermal decomposition of La(DPM)3 was promoted in the presence of Mn(DPM)3. The significant intermolecular interaction occurs between La and Mn precursors in the gas phase in MOCVD of lanthanum manganite films. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-13T04:40:07.260177-05:
      DOI: 10.1002/pssc.201510030
       
  • Hot‐wire vapor deposition of amorphous MoS2 thin films
    • Authors: Georgios Papadimitropoulos; Nikolaos Vourdas, A. Kontos, Maria Vasilopoulou, Dimitrios N. Kouvatsos, Nicolas Boukos, Alberto Gasparotto, Davide Barreca, Dimitrios Davazoglou
      Abstract: Amorphous, as shown by X‐ray diffraction measurements, MoS2 films (a‐MoS2) were deposited by heating a molybdenum wire at temperatures between 500 and 700 °C in H2S at 1 Torr. As shown by Scanning Electron Microscopy measurements, the morphology of samples depends significantly on the filament temperature; at low temperature samples are homogeneous and smooth, at intermediate temperatures they exhibit a granular microstructure and at high temperatures a columnar one. X‐ray photoelectron spectroscopy measurements have shown S/Mo ratios in films varying between 2.5 and 1.5 dependent on filament temperature. Films also contain oxygen at atomic contents of 8 to 12 %. As shown by XPS and Raman spectroscopy, at a filament temperature of 600 °C films are mainly composed of MoS2 also containing oxygen at an atomic ratio of 8%. Spectroscopic ellipsometry measurements made on a‐MoS2 films have shown that their band gap is of the order of 1.4 eV, slightly higher than that for the bulk crystalline material. Photoluminescence spectroscopy measurements have shown that samples exhibit a doublet of peaks at 2.8 and 3 eV blue shifted relatively to MoS2 samples composed of one or two mono‐layers. The above indicate that the electronic structure of crystalline atomic‐layer thick MoS2 is preserved in a‐MoS2 films. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-13T04:40:06.027588-05:
      DOI: 10.1002/pssc.201510031
       
  • Diamond crystals deposited from interacting jets
    • Authors: Aleksey Rebrov; Aleksey Emelyanov, Sergey Kosolobov, Ivan Yudin
      Abstract: This paper describes the advancement of hot wire or hot filament CVD methods of diamond synthesis through the use high velocity gas flow activation by multiple collisions with a lengthy hot surface instead of activation by single collisions with hot wires. The possibility of synthesis of diamond crystals from a neutral gas with a high growth rate and a future solution of engineering scaling problems promise that this method will become competitive with others. Interacting jets of hydrogen and mixture of hydrogen with methane were used to synthesize diamond crystals on a molybdenum substrate. The growth rate of crystals about 20 μm/h was attained, which is much higher than in the case of a hot filament CVD. The increase of CH4 concentration essentially increases the diamond crystal growth rate. Depending on local conditions of the interaction of jets with substrates in different points, a completely different morphology of deposit is observed: from a compact film to isolated coarse crystals mostly icosahedral form. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-13T04:40:04.666374-05:
      DOI: 10.1002/pssc.201510043
       
  • Electronic structure of threading dislocations in wurtzite GaN
    • Authors: I. Belabbas; J. Chen, G. Nouet
      Abstract: We have carried out atomistic simulations, based on density functional theory, to investigate the atomic and electronic structures of the three types of prismatic threading dislocations in hexagonal gallium nitride. Screw and mixed threading dislocations were demonstrated to introduce both deep and shallow gap states, while most of core configurations of the edge dislocation introduce solely shallow states. The higher electrical activity of both screw and mixed dislocations, compared to the edge one, is correlated with the high dispersion of their energy levels, within the GaN bandgap. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-13T04:30:13.232276-05:
      DOI: 10.1002/pssc.201400215
       
  • Impact of dopants and silicon structure dimensions on {113}‐defect
           formation during 2 MeV electron irradiation in an UHVEM
    • Authors: J. Vanhellemont; S. Anada, T. Nagase, H. Yasuda, A. Schulze, H. Bender, R. Rooyackers, A. Vandooren
      Abstract: When processing Si nanowire based Tunnel Field Effect Transistors (TFETS's), a significant reduction of B diffusion with decreasing nanowire diameter is observed and attributed to reduced transient enhanced diffusion close to the nanowire surface caused by the recombination and out‐diffusion of excess self‐interstitials. In this study, Ultra High Voltage Electron Microscopy (UHVEM) is used to study in situ the formation of self‐interstitial clusters in nanowire based TFET containing samples prepared by Focused Ion Beam (FIB) thinning. Si nanowires with diameters ranging from 40 to 500 nm are irradiated in an UHVEM using different fluxes of 2 MeV electrons at temperatures between room temperature and 375 °C. A strong dependence of defect formation on nanowire radius and on dopant concentration and type is observed. The UHVEM observations are compared with simulations based on quasi‐chemical reaction rate theory and with two dimensional dopant concentration distributions determined with high‐vacuum Scanning Spreading Resistance Microscopy (SSRM). (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-13T04:30:12.095424-05:
      DOI: 10.1002/pssc.201400222
       
  • Effect of O2 flow rate on the electrochromic response of WO3 grown by
           LPCVD
    • Authors: Konstantinos Psifis; Dimitris Louloudakis, Dimitra Vernardou, Emmanuel Spanakis, George Papadimitropoulos, Dimitris Davazoglou, Nikolaos Katsarakis, Emmanuel Koudoumas
      Abstract: Tungsten trioxide coatings were grown on fluorine doped tin dioxide glass substrate at 465 oC by low pressure chemical vapor deposition. Monoclinic tungsten oxide with low crystallinity containing agglomeration of grains was obtained irrespective of the O2 flow rate utilized. It was only observed an increase of grain size to 75 from 25 nm as the O2 raised to 100 from 25 sccm. In addition, the current density was similar among the samples irrespective of the growth conditions performed. Finally, the coloration efficiency was estimated to be 83 cm2 C‐1 at 670 nm, which is higher than other grown samples using greater deposition temperatures. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-13T04:30:11.06208-05:0
      DOI: 10.1002/pssc.201510004
       
  • Effect of O2 flow rate on the thermochromic performance of VO2 coatings
           grown by atmospheric pressure CVD
    • Authors: Dimitris Louloudakis; Dimitra Vernardou, Emmanouel Spanakis, Spyros Dokianakis, Marianthi Panagopoulou, Giannis Raptis, Elias Aperathitis, George Kiriakidis, Nikolaos Katsarakis, Emmanouel Koudoumas
      Abstract: This paper reports the atmospheric pressure chemical vapor deposition of vanadium oxide coatings using vanadyl (IV) acetylacetonate at 500 oC. The as‐grown samples for 0.8 L min‐1 O2 flow rate showed an (022)‐oriented single vanadium dioxide monoclinic phase of low crystallinity. The narrowest hysteresis width is observed for the particular flow rate indicating a dependency on the shape of the grown crystallites. Regarding the difference in transmittance is determined by the enhanced presence of short‐ and long‐range bond ordering of the samples. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-13T04:30:09.955649-05:
      DOI: 10.1002/pssc.201510005
       
  • Investigation of the kinetics of the chemical vapor deposition of aluminum
           from dimethylethylamine alane: experiments and computations
    • Authors: Ioannis G. Aviziotis; Thomas Duguet, Khaled Soussi, George Kokkoris, Nikolaos Cheimarios, Constantin Vahlas, Andreas G. Boudouvis
      Abstract: Experiments and computations are performed for the metalorganic chemical vapor deposition (MOCVD) of aluminum (Al) from dimethylethylamine alane (DMEAA). The deposition rate as a function of the substrate temperature and the evolution of the deposition rate along the radius of the susceptor are experimentally determined, in a vertical, warm wall MOCVD reactor operating at 10 Torr, in the temperature range 139 °C‐240 °C. Following previously published mechanism for the decomposition of DMEAA, a predictive 3D model of the process is built, based on the mass, momentum, energy and species transport equations with the aim to simulate the process. Taking into account experimental results it is demonstrated that a volumetric and a surface reaction are responsible for the deposition of Al from DMEAA. For both reactions, first order Arrhenius kinetics are implemented and the kinetic parameters are determined through fitting to the experimental data. The results show satisfactory agreement between experiments and computations for almost the whole temperature range examined. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-13T04:30:08.887113-05:
      DOI: 10.1002/pssc.201510023
       
  • Peculiarities of defect generation under injection current in LEDs based
           on A3N nanostructures
    • Authors: Natalia Shmidt; Evgeniia Shabunina, Alexander Usikov, Anton Chernyakov, Sergey Kurin, Hikki Helava, Yuri Makarov
      Abstract: It has been demonstrated that, along with well‐known mechanisms of defect generation (DG) under injection current in fabricated UV‐ and commercial blue‐LED chips based on A3N nanostructures, other defect generation mechanisms are possible in local regions. Aging experiments performed simultaneously with analysis of evolution of I‐V characteristics at U < 2 V and spectral noise density dependences on current density, revealed DG with participation of multi‐phonon recombination of carriers in an extended defect system and local regions of random alloy fluctuations enriched by metallic atoms (Ga or In). (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-11T06:10:32.205478-05:
      DOI: 10.1002/pssc.201400218
       
  • EBIC investigations of dislocations in ELOG GaN
    • Authors: E. B. Yakimov; A. Y. Polyakov
      Abstract: Dislocations in the ELOG n‐GaN films have been studied by the Electron Beam Induced Current (EBIC) method. The effect of dopant concentration and diffusion length values on the dislocation EBIC profile is revealed. It is shown that the width of dislocation image in the EBIC mode decreases with a diffusion length decrease and the dopant concentration increase. In the crystals with the submicron diffusion length the individual dislocations can be separated in the EBIC images up to the dislocation densities higher that 109cm‐2. The radius of dislocation related defect cylinder was found to increase with the dopant concentration decreasing that could be explained under an assumption that dislocations in GaN are charged. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-11T06:10:31.257827-05:
      DOI: 10.1002/pssc.201400220
       
  • About dislocation and oxygen related luminescence of Si around 0.8 eV
    • Authors: M. Kittler; T. Arguirov, M. Reiche, C. Krause, D. Mankovics
      Abstract: In conjunction with the two‐level model the temperature behaviour of the dislocation‐related D1‐peak follows the T‐behaviour of the band gap. Based on luminescence observations in our laboratory and on literature data we propose a ∼30 meV wide domain of the D1 peak. Altogether, the D1‐peak position ranges between about 0.76 eV at 300 K and nearly 0.84 eV at a few K. It was shown that the energetic shift for a certain temperature is caused by external electric fields, by excitation level, that affects the intrinsic dislocation field, and by elastic stress. The luminescence of oxygen‐related defects / precipitates might be described by a line at ∼ 0.77 eV (P‐line) that does not depend on temperature. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-11T06:10:30.379016-05:
      DOI: 10.1002/pssc.201400231
       
  • Materials characterization and device analysis for evaluation of
           semiconductor processes by highly‐sophisticated photoelastic stress
           measurement technique
    • Authors: Martin Herms; Matthias Wagner, Alexander Molchanov, Pinyen Lin, Ingrid De Wolf, Ming Zhao
      Abstract: SIRD (Scanning Infrared Depolarization Imager) and SIREX (Scanning Infrared Stress Explorer) are measurement systems to evaluate and visualize the stress distribution in semiconductor materials and devices. Some main fields of application are crystal growth, high temperature processing of silicon wafers as well as the 3D‐structuring of silicon‐based microelectronic devices. The used strategies of measurement are different. SIRD and SIREX are equipped with versatile software packages that allow to separate defect‐related stress states of interest, for instance slip‐lines in GaN‐overgrown silicon. Micro‐holes fabricated for wafer marking and 3D TSV (through silicon vias) structures have been analyzed with micrometer resolution. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-11T06:10:29.508895-05:
      DOI: 10.1002/pssc.201400356
       
  • A calculation method of deposition profiles in chemical vapor deposition
           reactors using bio‐inspired algorithms
    • Authors: Takahiro Takahashi; Taeka Inagaki, Shingo Nariai, Junichi Kodama, Masamoto Arakawa, Yoshinori Ema
      Abstract: Estimating the predicted results of experimental data by a simulator is one of the most important processes in deciding the performance of the automatic modeling system of reaction mechanisms in chemical vapor deposition (CVD). Therefore, we developed a novel calculation method, in which robust and accurate calculations along with reduced computing cost were achieved, to reproduce deposition profiles in the specific types of reactors. In order to improve the performance of the calculation method, we developed the method by use of the novel optimization algorithms, which are biologically inspired. We adopted real‐coded genetic algorithms (GAs) and artificial bee colony (ABC) as the bio‐inspired algorithms (BIAs). Boundary value problems for estimating diffusion‐reaction equations by iterations of numerical integrations were changed into problems of finding the linear combinations consisted of a few “basis functions”, which are ideally inherent in the reactors. The coefficients of the linear combinations were optimized by the BIAs. We demonstrate the improved performance of the simulator by the BIAs using the batch‐type reactor with round‐shaped substrates. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-07T03:23:55.696331-05:
      DOI: 10.1002/pssc.201510056
       
  • Gaseous ternary chromium‐aluminium complexes as precursor for
           chemical vapour deposition
    • Authors: Mario Lessiak; Roland Haubner, Reinhard Pitonak, Arno Köpf, Ronald Weissenbacher
      Abstract: Research on high‐performance CVD coatings follows the target to increased hardness and oxidation resistance. Such coatings and coating systems are required for machining tools to optimize the manufacturing parameters for new materials and new processes. The use of chromium‐containing coatings is requested because of its feature to increase the corrosion resistance. The production of various chromium‐containing coatings is already shown by PVD, but for industrial scale CVD processes there are problems with the chromium precursors. Especially the chromium chlorides have a low vapour pressure and therefore high temperatures are needed for evaporation. To overcome the disadvantages of CrCl3 the relatively good evaporation of halide complexes was reported, showing potential for new CVD processes. Numerous metal compounds form gaseous complexes with Aluminium chloride but also Cr. Based on this characteristic the transport reaction of CrCl2/Al2Cl6 as chromium tetrachloraluminate is investigated. The focus of this work lies in the preparation of the chromium precursors as well as in the optimization of the transport reaction which required various changes in the conventional experimental CVD‐setup. To measure the amount of transported chromium the gas phase was condensed and their Cr‐content was analyzed. For the CVD deposition of Cr containing coatings, this precursor gas flow can be used directly. Further the interaction between aluminum chloride and the chromium precursor, different process parameters, as well as existing difficulties regarding the transport reaction are discussed. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-07T03:13:37.004106-05:
      DOI: 10.1002/pssc.201510007
       
  • Kinetic study of MOCVD of NiO films from bis‐(ethylcyclopentadienyl)
           nickel
    • Authors: A. S. Kondrateva; M. Mishin, A. Shakhmin, M. Baryshnikova, S. E. Alexandrov
      Abstract: NiO films were grown by metal‐organic chemical vapor deposition (MOCVD) using bis‐(ethylcyclopentadienyl) nickel [(EtCp)2Ni] and oxygen or ozone as precursors. The kinetic regularities of MOCVD processes were experimentally studied in the deposition temperature range 600‐820 K for the reaction systems: (EtCp)2Ni–O2–Ar and (EtCp)2Ni–O3–O2–Ar. The results obtained show that the deposition processes in the temperature range 600‐700 K are controlled by kinetics and the value of activation energy of the processes is 80±5 kJ·mol−1 in both cases. The growth process in the temperature region 700–840 K is controlled by mass transport. An introduction of ozone in the reaction gas phase led to nearly twofold decrease of deposition rate probably because of homogeneous reactions with (EtCp)2Ni. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-07T03:13:35.98742-05:0
      DOI: 10.1002/pssc.201510014
       
  • CVD synthesis and catalytic combustion application of chromium oxide films
    • Authors: Jing Liang; Guan‐Fu Pan, Shi‐Bin Fan, Wei‐Liang Cheng, Zhen‐Yu Tian
      Abstract: Chromiumoxide (Cr2O3) thin films were controllably synthesized by pulsed‐spray evaporation chemical vapor deposition (PSE‐CVD) for deep oxidation of propene. The effect of substrate temperature on the growth kinetics and morphology of the films was investigated. The prepared samples were comprehensively characterized with respect to structure, morphology and surface composition with XRD, SEM and XPS, respectively. An in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was involved to reveal the surface mechanism occurred on Cr2O3. The growth rate exhibited a linear behavior when the temperature increase from 300 to 450 °C. The structural analysis indicated that a pure phase of Cr2O3 was obtained at 425 °C. The catalytic tests showed that Cr2O3 films prepared on flexible substrates exhibited advantages for the catalytic oxidation of C3H6. Based on the DRIFTS observations, the Langmuir‐Hinshelwood (L‐H) mechanism was proposed for C3H6 over Cr2O3 films. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-07T03:13:35.103864-05:
      DOI: 10.1002/pssc.201510019
       
  • CVD nanographite films covered by ALD metal oxides: structural and field
           emission properties
    • Authors: Rinat R. Ismagilov; Feruza T. Tuyakova, Victor I. Kleshch, Ekaterina A. Obraztsova, Alexander N. Obraztsov
      Abstract: Nanographite films produced by direct current plasma enhanced chemical vapour deposition technique were covered by metal oxides TiO2 and Al2O3 using atomic layer deposition. Nanographite films are composed of few‐layer graphene nanowalls and nanoscrolls, which are mostly oriented perpendicular to the silicon substrate surface. The nanographite and nanographite‐metal oxide composite film materials, with oxide layer thickness between 50 nm and 250 nm, were characterized by scanning electron microscopy, energy dispersive X‐ray analysis, thermal gravimetric analysis, and Raman spectroscopy. We demonstrate that the metal oxide deposit homogenously covers graphene nanowalls and forms individual spherical particles on the surface of needle‐like nanoscrolls. Field emission properties of the samples were measured in a flat vacuum diode configuration. It was found that the metal oxide layers thinner than 200 nm do not significantly affect the field emission characteristics of the nanographite. At the same time, metal oxides form a passivation shell which may improve the nanographite film performance as cold cathode in vacuum electronic devices. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-07T03:13:34.09799-05:0
      DOI: 10.1002/pssc.201510022
       
  • Effect of substrate temperature on initiated plasma enhanced chemical
           vapor deposition of PHEMA thin films
    • Authors: Mehmet Gürsoy; Mustafa Karaman
      Abstract: Poly(2‐hydroxyethyl methacrylate) (PHEMA) thin films were deposited on silicon wafers by initiated plasma enhanced chemical vapour deposition (i‐PECVD) method at different substrate temperatures. Di tert‐butyl peroxide (TBPO) was used as an initiator, and all deposition experiments were performed at 3:1 monomer to initiator flow ratio. Deposition rates up to 44 nm/min were observed at relatively low plasma power depending on the deposition conditions. The high deposition rates at low plasma powers were attributed to the usage of the initiator. Fourier transform infrared spectroscopy (FTIR) and X‐ray photoelectron spectroscopy (XPS) analyses of the deposits indicated very high retention of hydroxyl and carbonyl functionalities especially for the polymers deposited at low plasma powers. Water contact angle measurements were carried out to determine the wettability of as‐deposited PHEMA surfaces. This study indicated that the substrate temperature is an important parameter determining the polymerization rate. Being a dry, low‐cost, reliable and environmentally friendly process, the i‐PECVD technique developed in this study can be used to deposit other functional polymers. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-07T03:13:33.227986-05:
      DOI: 10.1002/pssc.201510034
       
  • Time‐scale analysis of atomic layer deposition processes: Predicting
           the transition from mass‐transfer to kinetically limited regimes
    • Authors: Raymond A. Adomaitis
      Abstract: The relative rates of adsorption and irreversible reaction are modeled for a prototypical atomic layer deposition (ALD) system. Surface species balance modeling equations are processed through a reaction factorization procedure to eliminate redundant dynamic modes. The resulting singular perturbation problem then is used to develop a criterion that distinguishes between mass‐transfer and kinetically‐limited deposition regimes for this dynamic process. Detailed simulations of a TMA/water alumina ALD process are used to evaluate our analysis approach and to demonstrate the dominance of mass‐transfer limitations for this system during both precursor exposure periods. Our analysis shows the increasing likelihood of encountering mass‐transfer limitations at reduced temperatures, a finding opposite of what might be expected. We find that the ALD dynamics evolve on a manifold defined by the balancing of adsorption and irreversible reaction rates, further reducing the dynamic dimension of the deposition dynamics. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-07T03:13:32.139295-05:
      DOI: 10.1002/pssc.201510048
       
  • The automatic experimental design for modeling the reaction mechanisms of
           chemical vapor deposition processes
    • Authors: Takahiro Takahashi; Yoshinori Ema
      Abstract: The identification of an appropriate reaction model (reaction mechanism) that indicates the reaction paths from source gases to films is one of the most important facets for developing chemical vapor deposition (CVD) processes. Previously, we developed a system that automatically identifies the kinetic models of reaction mechanisms involved in experimental results by the CVD processes using genetic algorithms (GAs). However, in order to automate the entire process of CVD development, it is necessary to automate the other processes associated with the reaction‐modeling process. Therefore, in this study, we proposed the method to automate the experimental design to determine more appropriate the reaction models. In addition, we developed the automatic system to design the experiments for the models. We demonstrated the feasibility and validity of the method using a simplified and synthetic CVD process. The system automatically and appropriately designed the experiments from the information of the reaction model candidates without using the knowledge of reaction engineering directly. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-07T03:13:31.242865-05:
      DOI: 10.1002/pssc.201510052
       
  • Ab‐initio study of ferromagnetism in Mn‐doped ZnSnAs2
    • Authors: Vusala Jafarova; Suma Huseynova, Guseyn Orudzhev, Naotaka Uchitomi, Kazuki Wakita, Nazim Mamedov
      Abstract: The electronic and magnetic properties of pure as well as Mn‐doped chalcopyrite semiconductor ZnSnAs2 were studied by the DFT+U ab initio method within the spin generalized gradient approximation. The band structure and DOS calculations resulted in a direct gap scenario for semiconducting ZnSnAs2. The energy gap of 0.34 eV occurs at the center of the Brillouin zone and linearly increases with increasing Mn concentration x at a rate of 2.05 eV for x < 0.03. The total energy calculations for a number of supercells showed that a ferromagnetic rather than antiferromagnetic ordering is favorable in Mn‐doped ZnSnAs2 when Mn replaced Sn. The energy deficient substitution of Zn by Mn led to the antiferromagnetic ordering. The magnetic moment per Mn atom, together with contribution of each atom into the total moment of ZnSnAs2: Mn was determined. The contributions from Mn and As are dominant but have opposite signs. Besides, the As atoms chemically bounded to Mn dopant were found to be most contributive. At last it was shown that the vacancies such as V(Zn), V(Sn), and V(As) affect the magnetic properties and may even strengthen the magnetization of Mn‐doped ZnSnAs2. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-07T03:13:29.991945-05:
      DOI: 10.1002/pssc.201400355
       
  • Luminescent property and mechanism of ZnAl2O4 ultraviolet emitting
           phosphor
    • Authors: Takeaki Ishinaga; Taku Iguchi, Hiroko Kominami, Kazuhiko Hara, Mamoru Kitaura, Akimasa Ohnishi
      Abstract: ZnAl2O4 ultraviolet (UV) emitting phosphor has been studied for next‐generation ultraviolet emission device. In this work, to investigate the mechanism of ZnAl2O4, the phosphor was evaluated and analyzed using various methods. It is thought that the optimum ratio of source materials to obtain the single phase of ZnAl2O4 is 0.975. UV emission peak of ZnAl2O4 was changed from around 250 nm to 270 nm and the absorption edge was shifted to lower energy as increase the ratio of source materials. It is thought that bandgap of ZnAl2O4 became narrower as increase the ratio of source materials. From the results of annealing in active carbon, it became clear that the UV emission from ZnAl2O4 was caused oxygen vacancy. Additionally, from the results of sterilization examination, it is thought that the properties of ZnAl2O4 are promising for using it as candidate for sterilization. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-07T03:13:28.817776-05:
      DOI: 10.1002/pssc.201400317
       
  • Growth of β‐gallium oxide films and nanostructures by
           atmospheric‐ pressure CVD using gallium and water as source
           materials
    • Authors: Tomoaki Terasako; Hikaru Ichinotani, Masakazu Yagi
      Abstract: Films and nanostructures of β‐Ga2O3 were successfully grown by atmospheric‐pressure CVD (AP‐CVD) using metal Ga and H2O as source materials. It was confirmed that highly (‐201) oriented polycrystalline β‐Ga2O3 films can be obtained on c ‐plane sapphire (c ‐Al2O3) substrates by optimizing growth temperature (Tg) and source supply ratio of H2O to Ga. The optical gap energy of the β‐Ga2O3 film with a relatively flat surface was estimated to be ∼4.9 eV. Photoluminescence (PL) measurements for the β‐Ga2O3 films revealed the existence of at least three emission bands with their peaks at ∼370 nm, ∼440 nm and ∼520 nm. Various shapes of quasi 1D nanostructures, such as nanowires (NWs), nanorods (NRs), tapered NRs and nanobelts (NBs), were obtained on the c ‐Al2O3 substrates coated with the Au films by utilizing vapour‐liquid‐solid (VLS) growth mechanism. The diversity of the quasi 1D nanostructures is probably due to the contribution of vapour‐solid (VS) growth mechanism and/or the coalescence between the neighbouring Au metal particles before initiating the NW (or NR) growth. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-07T03:13:27.86977-05:0
      DOI: 10.1002/pssc.201510012
       
  • Bismuth‐doped Cu(In,Ga)Se2 absorber prepared by multi‐layer
           precursor method and its solar cell
    • Authors: Jakapan Chantana; Daisuke Hironiwa, Taichi Watanabe, Seiki Teraji, Kazunori Kawamura, Takashi Minemoto
      Abstract: Bismuth (Bi)‐doped Cu(In,Ga)Se2 (CIGS) films were prepared by the so‐called “multi‐layer precursor method”, obtained by depositing them onto Bi layers with various thicknesses on Mo‐coated soda‐lime glass (SLG) substrates. Material composition (Cu, In, Ga, and Se) profiles of the CIGS films are almost identical, whereas sodium (Na) is reduced, when Bi thickness is increased. Moreover, the incorporation of Bi into the CIGS film is enhanced with thicker Bi layer. With Bi thickness from 0 to 70 nm, the 2.4‐μm‐thick CIGS absorbers demonstrate the increase in CIGS grain size, carrier lifetime, and carrier concentration, thus improving their cell performances, especially open‐circuit voltage (VOC). With further increase in Bi thickness of above 70 nm, the CIGS films show the deterioration of CIGS film quality owing to the formation of Bi compounds such as Bi, BiSe, and Bi4Se3. Consequently, Bi‐doped CIGS absorber with thickness of 2.4 μm, prepared with the 70‐nm‐thick Bi layer on Mo‐coated SLG substrate, gives rise to the improvement of photovoltaic performances, especially VOC. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-05T08:10:39.569338-05:
      DOI: 10.1002/pssc.201400239
       
  • Thin film growth of Cd1‐xZnxTe and its application to X‐ray
           sensor
    • Authors: K. Mochizuki; J. Takahashi, N. Nakamura
      Abstract: Cd1‐xZnxTe (x∼0.5) thin films with less than 300μm are grown on ITO/glass substrate by Hot‐wall and PVT methods, one of the sublimation methods. In order to obtain the films with high resistivity and good quality for X‐ray sensor, three attempts have been tried in the experiments. The one is stoichiometry control of CZT (x = 0.04) films, which were grown under controlled Cd vapor pressure. The second is excess chlorine doping to the films (x = 0.04) by controlling CdCl2 vapor pressure during growth process. The third is to change composition x = 0.04‐0.50, which increases band gap. Through these methods, best films with good X‐ray response was obtained for the third case of the films with the composition x = 0.20. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-05T08:10:38.736196-05:
      DOI: 10.1002/pssc.201400264
       
  • Effect of preheating time on uniformity of electrodeposited Cu2ZnSnS4 thin
           films studied by carrier lifetime and photoluminescence measurements
    • Authors: T. Hamada; A. Fukuyama, F. Jiang, S. Ikeda, T. Ikari
      Abstract: Cu2ZnSnS4 (CZTS) is paid attention to the low‐cost and nontoxic solar cell material. In this study, CZTS thin film was deposited by using an electrodeposition technique followed by a sulfurization after preheating the deposited metallic precursor layer. We investigated the film properties of CZTS thin films for understanding the effect of preheating time on the photovoltaic properties such as carrier lifetime and recombination mechanism by using a microwave photoconductivity decay (μ‐PCD) and a photoluminescence (PL) measurement. The results of the μ‐PCD measurements showed that carrier lifetime increased with increasing the preheating time and longer carrier lifetime was observed in a part of deposited thin film. The PL measurements showed the peak energy shift to lower energy region by a surface position of the sample preheated for 150 min. We found the CZTS crystal quality improved but the homogeneity worsened with increasing the preheating time. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-05T08:10:37.428163-05:
      DOI: 10.1002/pssc.201400283
       
  • Preparation and characterization of Cu2Six Sn1‐xS3
    • Authors: Kotoba Toyonaga; Hideaki Araki
      Abstract: Cu2SnS3 is a promising compound for use as an absorber layer in thin film solar cells because it is made up of low‐cost and abundant elements, and has a high optical absorption coefficient. However, the band gap energy of monoclinic Cu2SnS3 is less than the value required for absorber layers in single‐junction solar cells. On the other hand, the band gap energy of Cu2SiS3 was reported to be approximately 2.5 eV, which is sufficiently large for this purpose. Therefore, in the present study, an attempt was made to synthesize Cu2Six Sn1‐xS3, which is a solid solution between Cu2SnS3 and Cu2SiS3. In X‐ray diffraction patterns from the synthesized compounds, the diffraction peaks were found to shift to higher 2θ values with increasing x, indicating a decrease in the lattice constants. In addition, the estimated band gap energy increased from 0.85 to 2.56 eV with increasing x. Cu2Six Sn1‐xS3 is therefore a potential candidate for use as the absorber layer in thin film solar cells because its band gap energy can be adjusted simply by varying its composition. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-05T07:40:45.917093-05:
      DOI: 10.1002/pssc.201400296
       
  • Growth and characterization of Ga doped ZnSnAs2 thin films on InP
           substrates
    • Authors: Takahiro Kato; Takashi Uchiyama, Hideyuki Toyota, Naotaka Uchitomi
      Abstract: We have grown Ga doped ZnSnAs2 thin films on InP substrates using all‐solid source MBE technique. Using the optimum substrate temperature of 340 ºC and Zn:Sn:As4 beam equivalent pressure ratio (BEPR) of 24:1:52, samples were prepared with different Ga concentration achieved by changing the Ga flux. Compositional analysis was performed using electron microprobe microanalysis (EMPA). We found that Ga concentration on the cation sites is 20.9% and 8.7%. XRD patterns of Ga doped samples showed only assignable to ZnSnAs2:Ga and InP substrate. The lattice constant decreases linearly from 0.5862 to 0.5829 nm with decreasing Ga concentration. The observed concentration dependence indicates that the lattice constant of the thin films can be controlled by Ga doping concentration. Hall coefficient and resistivity of Ga 8.7 % doped sample can be well explained by the impurity band model. We were able to resolve the experimentally obtained carrier concentration pexp and mobility μexp into valence band carrier concentration pv with mobility μv and acceptor band carrier concentration pa with mobility μa. The computed apparent values papp and μapp are in good agreement with pexp and μexp, respectively. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-05T07:40:44.528067-05:
      DOI: 10.1002/pssc.201400295
       
  • Fabrication of 5.2% efficient Cu2ZnSn(S,Se)4 solar cells using
           DC‐sputtered metal precursors followed by sulfo‐selenization
    • Authors: Han Sung Yang; Ganesh Agawane, Seung Wook Shin, Sharadrao Vanalakar, Woo Lim Jung, Jin Hyeok Kim
      Abstract: In this study, we report Cu2ZnSn(S,Se)4 (CZTSSe) thin films synthesized by using a rapid thermal annealing process of direct current sputtered precursors under a sulfur and selenium atmosphere. X‐ray diffraction and Raman spectroscopy investigations showed formation of CZTSSe absorber layer without any secondary phase. X‐ray fluorescence spectroscopy showed a stoichiometric absorber layer has been formed which is suitable for use in solar cells. The best thin film solar cell of CZTSSe showed a photovoltaic performance of 5.2% efficiency (Voc: 585.0 mV, Jsc: 17.0 mA/cm2 and FF: 52.0%). This is the highest efficiency reported for CZTSSe prepared from sputtered Cu/Zn/Sn precursors followed by sulfo‐selenization using powder sources. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-05T07:40:43.603596-05:
      DOI: 10.1002/pssc.201400287
       
  • Synthesis of Cu(In,Ga)Se2 crystals using a crank ball mill
    • Authors: Suzuka Yamada; Hideki Noji, Tomoichiro Okamoto, Yoji Akaki
      Abstract: Cu(In,Ga)Se2 (CIGS) crystals were synthesized by a mechanochemical (MC) process using a crank ball mill. The molar ratios of starting materials were Cu:In:Ga:Se=1:1‐x:x:2 (0≤x≤1) and Cu:In:Ga:Se=1:0.7:0.3:y (2≤y≤3). The reaction time reduced with decreasing Se and Ga molar ratios. The collection rate decreased with longer reaction times. From XRD patterns, we confirmed that the CuInSe2 and/or CuGaSe2crystals were successfully grown when the powders reacted. Although the crystals grown with a selenium molar ration of 2 were Se‐poor, those grown at a molar ratio of 3 were Se‐rich. When Se increasing molar ratio, Cu, In, and Ga were away from the stoichiometric. With a molar ratio of Cu:In:Ga:Se=1:0.7:0.3:2.5∼2.7, their composition became stoichiometric. Crystal morphology was varied. CIGS crystals were thus successfully synthesized using a crank ball mill. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-05T07:40:42.472061-05:
      DOI: 10.1002/pssc.201400327
       
  • Spectroscopic ellipsometry studies of as‐prepared and annealed CdS:O
           thin films
    • Authors: Khuraman Khalilova; YongGu Shim, Ilham Hasanov, Ryo Asaba, Kazuki Wakita, Nazim Mamedov
      Abstract: Cadmium sulfide thin films on soda lime substrates were obtained by rf‐magnetron sputtering in argon‐oxygen atmosphere. As‐prepared and vacuum annealed films were then studied by spectroscopic ellipsometry at room temperature over photon energy range from 0.5 to 6 eV. The obtained ellipsometric data were treated using optical dispersion models based on Gaussian type oscillators. Dielectric function of oxygen‐free films, as well as those obtained under 3% of O/Ar partial pressure was reliably restored. At the same time, dielectric function obtained for 5% CdS:O can be regarded only as an average over several materials since our XPS examination disclosed presence of several compounds in thin films deposited at O/Ar ratios higher than 3%. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-05T07:40:41.579987-05:
      DOI: 10.1002/pssc.201400272
       
  • Ab initio calculations of phonon dispersion and lattice dynamics in
           TlGaTe2
    • Authors: Vusala Jafarova; Guseyn Orudzhev, Raul Paucar, Oktay Alekperov, YongGu Shim, Kazuki Wakita, Nazim Mamedov, Nadir Abdullayev, Arzu Najafov
      Abstract: This work reports the results of DFT‐based calculations of phonon spectra of TlGaTe2. The dispersion of phonon bands was calculated along the directions of Brillouin zone (BZ) that include symmetry points. The calculated phonon frequencies at the centre of BZ were compared with those obtained by Raman spectroscopy with the aid of a confocal laser microscopy system. A fairly good agreement between the calculated and experimental data was found. Complimentary, molar heat capacity at constant volume and Debye temperature were calculated in the range 5÷500 K on the base of the obtained phonon density of states. The obtained temperature dependencies were compared with available experimental data.The results of comparison were satisfactory. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-05T07:40:39.969455-05:
      DOI: 10.1002/pssc.201400351
       
  • Interaction of methyl radical (CH3) with C60 fullerene: Density functional
           theory (DFT) study
    • Authors: Hiroto Tachikawa; Tetsuji Iyama
      Abstract: The addition reaction of methyl radical (CH3) to fullerene (C60) surface has been investigated by means of density functional theory (DFT) method. The DFT calculation showed that the CH3 radical binds directly to the carbon atom of C60 and a strong C‐C single bond is formed. The binding energy of CH3 to C60was calculated to be 35.1 kcal/mol at the CAM‐B3LYP/6‐311G(d,p) level. The potential energy curve plotted as a function of a distance of CH3 from the C60 surface showed that the CH3 radical can approach to the carbon atom with very low activation barrier: the barrier height was calculated to be 2.8 kcal/mol. The electronic states of CH3‐C60 complex were discussed on the basis of theoretical results. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-05T07:40:38.696866-05:
      DOI: 10.1002/pssc.201400354
       
  • Temperature dependent spectroscopic ellipsometry of Ag2Se and Ag2S with
           phase transitions from ionic to superionic conductivity state
    • Authors: O. Alekperov; N. Gasimov, Kh. Khalilova, Y. Shim, R. Paucar, N. Abdulzade, O. Samedov, Z. Jahangirli, E. Nakhmedov, K. Wakita, N. Mamedov
      Abstract: Temperature dependent infrared (IR) and optical spectroscopic ellipsometry methods are used to investigate peculiarities of the transitions from the ionic conductivity to the superionic conductivity states in Ag2S and Ag2Se compounds. The structural phase transitions (SPTs), known as β→α transition in these semiconductors, are investigated also with spectroscopic ellipsometry methods. The electronic band structure of Ag2S at the SPT changes sharply from the monoclinic to the bcc phase, which occurs at T = 453 K in the super ionic conductivity state, where all the interband transitions in optic region, corresponding to the monoclinic structure of β‐phase, disappear. The α‐phase of Ag2S is characterised with new lines in the dielectric functions ε1 and ε2, which arise at 5‐6.5 eV. The interband transitions do not change in the SPT from the orthorhombic to the bcc in Ag2Se, which occurs at T > 406 K. In IR ellipsometry for the degenerated Ag2Se, the free carriers' plasma energy is displaced abruptly from ħω=0.075 eV at T=300 K to ħω=0.125 eV at T=338 K. The same effect is seen in the IR ellipsometry for Ag2S, where negative ε1 appears at T=434‐440 K. These facts indicate a drastic increase of the free carriers concentrations in both of the semiconductors at temperatures before the β→α SPT. In Ag2S the second abrupt shift of the free carriers plasma energy from 0.035eV to 0.1 eV occurs at T=453 K, corresponding to β→ α SPT. The second shift is due to the electronic band structure change of Ag2S. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-05T07:40:37.67887-05:0
      DOI: 10.1002/pssc.201400367
       
  • Mechanical, electronic, and optical properties of the A4B6 layered
           ferroelectrics: ab initio calculation
    • Authors: Husnu Koc; Sevket Simsek, Selami Palaz, Oral Oltulu, Amirullah M. Mamedov, Ekmel Ozbay
      Abstract: We have performed a first principles study of the structural, elastic and electronic properties of orthorhombic SnS and GeS compounds using the density functional theory within the local density approximation. The second‐order elastic constants have been calculated, and the other related quantities such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities, Debye temperature, and hardness have also been estimated in the present work. All of the calculated modulus and Poisson's ratio for SnS were less than the same parameters for GeS. Our calculations have discovered the large anisotropy of elastic parameters in the (100) and (010)‐planes for both compounds. The band structures of orthorhombic SnS and GeS have been calculated along high symmetry directions in the first Brillouin zone (BZ). The calculation results for the band gap of Sn(Ge)S gave Eg = 0.256 eV (0.852 eV) and has an indirect character for an interband transition. The real and imaginary parts of dielectric functions and (by using these results) the optical constant such as energy‐loss function, the effective number of valance electrons and the effective optical dielectric constant were calculated. All of the principal features and singularities of the dielectric functions for both compounds were found in the energy region between 2 eV and 20 eV. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-05T07:40:36.016366-05:
      DOI: 10.1002/pssc.201400245
       
  • Optimization of CIGSe bottom cell for spectral splitting device
           application
    • Authors: Z. Jehl‐Li‐Kao; Hirofumi Fukai, Isamu Matsuyama, T. Nakada
      Abstract: We investigate on narrow bandgap CIGSe solar cells for tandem application in a spectral splitting devices. Numerical simulations using SCAPS are performed to optimize the Ga content throughout the absorber layer, depending on the illumination condition (AM 1.5 and tandem conditions using two different splitting filters; 620 nm and 880 nm). The simulations show a strong dependence of the efficiency on the minimum bandgap of the absorber, but not on the depth of the narrow bandgap region. Narrow bandgap CIGSe solar cells are experimentally realized and electrically characterized. A similar trend as what was deduced from the simulation is observed on the experiments when the solar cells are characterized in the tandem conditions. For the 880 nm splitting filter, an efficiency of 5.5% is experimentally obtained with a minimum bandgap of 1.05 eV. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-05T07:40:35.001401-05:
      DOI: 10.1002/pssc.201400308
       
  • IR ellipsometry of silk fibroin films on Al nanoislands
    • Authors: Oktay K. Gasymov; Arzu Aydemirova, Oktay Alekperov, Rasim B. Aslanov, Khuraman Khalilova, Nagi Gasimov, Nazim Mamedov, Irada Mamedova, Sardar Babayev, Namig Gasanov
      Abstract: Infrared spectroscopic ellipsometry (IRSE) is a powerful tool for the characterization of various types of organic and inorganic films. In application to protein films, IRSE can be utilized to detect structural changes, orientation of specific group, etc. Because of sensitivity, enhanced IRSE will be very useful to study protein thin films. Here we show that fibroin films on Al mirror display surface‐enhanced infrared spectroscopic ellipsometry (SEIRSE). AFM data indicate that nanoislands on the Al mirror are responsible for the plasmon‐enhanced mechanism. SEIRSE for fibroin films shows non‐uniform enhancement across the spectrum. Possible mechanisms of such enhancement are provided. Evidently, as proposed previously, at least two mechanisms, the electromagnetic (EM) and chemical, are expected to contribute to the enhancement. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-05-05T07:40:34.065021-05:
      DOI: 10.1002/pssc.201500005
       
  • Impedance spectroscopy study of phase transitions to ionic and superionic
           conductivity states in Ag2S and Ag2Se
    • Authors: O. Alekperov; O. Samedov, R. Paucar, N. Abdulzade, E. Nakhmedov, A. Nadjafov, K. Wakita, N. Mamedov
      Abstract: The percolation threshold (PT) temperatures Tc1,c2 of two non‐equivalent Ag+1,2 ions in Ag2S and Ag2Se lattices were determined from the temperature dependence of low‐frequency (25‐106Hz) impedance spectroscopy measurements. At PT temperatures Tc1≈200 K and Tc2≈ 334 K, an abrupt increase of the dielectric function ε1(ω) of Ag2Se crystal from a very large negative value, ε1 ≈‐109, to a very large positive value ε1≈ 106 was observed, which is assumed to result from the dipole relaxation. The strong peaks of the dielectric losses ε2(ω), tgδ(ω) and impedance Z in Ag2Se were also determined at Tc1,c2. Two significant peaks in ε1(ω), ε2(ω)and tgδ(ω) were observed at Tc1≈ 312‐320 K. and Tc2≈ 380‐430 K in the temperature dependences of these parameters. The measured parameters decreased significantly with increasing frequency, confirming the long relaxation times. The drastic decrease at T > 430 K of ε1from a very large positive value 109to a very large negative one ‐108 is in accordance with infrared (IR) ellipsometry measurements; this indicates that electrons of Ag+‐ ions are ionized because of the high dielectric function screening of lattice sites before the known β→α structural phase transition from monoclinic to a body‐centered cubic (bcc) structure. In addition, the activation energies of Ag+1,2 ions were estimated for Ag2S and Ag2Se crystals. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-24T03:30:08.269573-05:
      DOI: 10.1002/pssc.201400366
       
  • Advancement in treating some features of CIGS thin film solar cells during
           manufacturing
    • Authors: Poonam Sharma; Zhongli Li, Hsueh Hsin Chang, Arya Jagadhamma Letha, Lexi Shao, Yafei Zhang, Huey Liang Hwang
      Abstract: In‐line sputtering and selenization have become the industrial standard, but it is difficult to predict and control the local chemical composition of the film. The present communication reports on the material design, device design and process design. These designs use parameters that are closely related to their chemical compositions, as a variation in composition leads to modification of the Poisson equation, current equation and continuity equation. Therefore, there is a need to build a model that relates the optoelectrical properties and device structural parameters that will be loaded into the process simulation, to obtain the complete set of process control parameters. The detailed optical and electrical properties are also investigated for the development of an analytical solar cell simulator. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-24T03:30:06.90874-05:0
      DOI: 10.1002/pssc.201400315
       
  • Control of extended defects in cast multicrystalline silicon using
           polycrystalline template
    • Authors: Ronit R. Prakash; Karolin Jiptner, Jun Chen, Yoshiji Miyamura, Hirofumi Harada, Takashi Sekiguchi
      Abstract: Extended defects were controlled using polycrystalline silicon as a template for cast‐growth of multicrystalline silicon. At the initial stage of growth, small randomly oriented grains with a high density of random type grain boundaries were obtained. With growth, the grain size increased and the fraction of random grain boundaries decreased. Electrical activity of defects was investigated and it was found that with growth, network of small angle grain boundaries became the most electrically active defects. This network of small angle grain boundaries were found to have a tilt angle less than 3° and were mainly found in elongating grains. The density of these highly electrically active grain boundaries increased with growth. This can be attributed to propagation and agglomeration of dislocations into small angle grain boundaries. The high density of random grain boundaries in this ingot may suppress dislocation propagation between grains, however they do not intersect elongating grains enabling dislocation propagation in elongated grains. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-24T03:30:05.844509-05:
      DOI: 10.1002/pssc.201400299
       
  • Structural characterisation of Cu2.04Zn0.91Sn1.05S2.08Se1.92
    • Authors: G. Gurieva; M. Dimitrievska, S. Zander, A. Pérez‐Rodríguez, V. Izquierdo‐Roca, S. Schorr
      Abstract: Quaternary Cu2ZnSn(S1‐xSex)4 compounds are promising semiconductor materials for absorber layer in thin film solar cells. Record efficiency devices (12.6%) exhibit an off‐stoichiometric composition of the absorber layer. These deviations from stoichiometry cause intrinsic point defects, which determine the electronic properties of the semiconductor significantly. A structural analysis of a nearly C‐type off‐stoichiometric Cu and Sn rich and Zn poor Cu2ZnSn(S1‐xSex)4 mixed crystal with x=0.48 by a neutron diffraction investigation was performed. The average neutron scattering length method was applied, showing that the mixed crystal adopts the kesterite type structure. A detailed cation distribution analysis revealed the occurrence of ZnCu(2a) and SnZn anti‐site point defects additional to the Cu‐Zn disorder in the planes at z=1/4 and 3/4. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-22T05:30:23.574279-05:
      DOI: 10.1002/pssc.201400307
       
  • Optimization of preparation techno‐ logy of ZnO and ZnO: Al thin
           films for solar cell applications
    • Authors: Elnur Bagiyev; Narmina Balayeva, Yegana Aliyeva, Afet Kerimova, Rusif Valiyev, Zamin Mamiyev, Nagi Gasimov, Ayaz Bayramov
      Abstract: ZnO and ZnO: Al thin films of about 100 nm thicknesses were deposited by magnetron sputtering method at 200‐400 °C substrate temperatures under oxygen/argon gas mixture with different O/Ar ratio (0‐6 %O2). The higher crystallinities for ZnO: Al and ZnO films are achieved at 400 °C substrate temperature under 0 % and 4 % (O/Ar) mixture ratios, respectively. The films were characterized by X‐ray diffraction (XRD), spectroscopic ellipsometery (SE), photoluminescence spectroscopy, and atomic force microscopy (AFM) methods. Electrical, optical, and luminescent properties depending on crystallinities of the obtained films were studied. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-22T05:30:22.542009-05:
      DOI: 10.1002/pssc.201400364
       
  • Variable range hopping conductivity at low temperatures in CuGaS2 single
           crystals
    • Authors: N. A. Abdullayev; Kh. V. Aliquliyeva, I. Qasimoglu, T. G. Kerimova, I. A. Mamedova
      Abstract: Charge transport mechanism in the CuGaS2 single crystals in a wide temperature range 4.3‐300 K are investigated. In the high temperature range 100‐300 K, the electrical conductivity is predominantly provided by thermally excited impurity charge carriers in the allowed energy band. The activation energy for impurity charge carriers in this temperature range is equal to 12 meV. In the low temperature range (T < 100 K), the electrical conductivity occurs through charge carrier hopping between localized states lying in a narrow energy band near the Fermi level (so called Mott conductivity). The density of localized states near the Fermi level, the width of the optimum energy band of localized levels, concentration of localized states and the average carrier‐hopping distances are estimated for different temperatures. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-22T05:30:21.491314-05:
      DOI: 10.1002/pssc.201400339
       
  • Metallic conductivity and weak antilocalization in Bi2Te2.7Se0.3 thin
           films
    • Authors: Nadir A. Abdullayev; Afet M. Kerimova, Khayala V. Aliquliyeva, Yong Gu Shim, Kojiro Mimura, Kazuki Wakita, Oktay Z. Alekperov, Nazim T. Mamedov, Vladimir N. Zverev
      Abstract: Submicron thin films of Bi2Te2,7Se0,3 solid solution is synthesized by thermal vacuum evaporation. The films are then subjected to after‐growth vacuum annealing and characterized using X‐ray diffraction and confocal laser microscopy techniques. Electron transport in the synthesized films is studied over the temperature range of 1.4‐300 K at magnetic fields up to 8 T. Electron localization due to electron‐electron interaction, along with weak anti‐localization effect at weak magnetic fields and temperatures below 8 K is observed. The latter effect is commonly encountered in thin films of topological insulators grown by molecular beam epitaxy and has therefore been ascribed to the manifestation of the topological surface states. Finally, phase coherence length is estimated.
      PubDate: 2015-04-22T05:30:20.305072-05:
      DOI: 10.1002/pssc.201400338
       
  • Preparation of europium‐doped GaN and AlGaN films grown by
           radical‐nitrogen‐assisted compound‐source MBE
    • Authors: Shinji Yudate; Yuki Koyama, Sho Shirakata
      Abstract: By the compound‐source molecular beam epitaxy (CS‐MBE), GaN:Eu and AlGaN films grown on both Al2O3(0001) and GaAs(100) substrates were prepared. Under RHEED observation, streak RHEED patterns from GaN were observed. This result shows that the surface of the film grown by CS‐MBE is atomically flat. From the XRD measurements, for GaN:Eu/Al2O3(0001), the film was oriented to c‐axis. On the other hands, for GaN:Eu/GaAs(100), the layer includes both the hexagonal and cubic phases. From the PL measurements, the PL spectra of both GaN:Eu/Al2O3 and GaN:Eu/GaAs(100) showed PL peaks related to Eu3+ ion. For GaN:Eu/GaAs(100), it is possible that part of Eu atom incorporates cubic‐GaN site (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-22T05:30:19.298999-05:
      DOI: 10.1002/pssc.201400330
       
  • Improvement of In2S3/ZnCuInS2 interfaces for wide‐gap solar cells
    • Authors: Teruaki Yamamoto; Takayuki Negami, Koji Matsubara, Shigeru Niki
      Abstract: We have fabricated superstrate In2S3/ZnCuInS2 (Zn2xCu1‐xIn1‐xS2, ZCIS) solar cells as the top cell of multi‐junction solar cells. The ZCIS and In2S3 thin films were deposited by spray pyrolysis deposition (SPD) and an efficiency of 4.4% was achieved with bandgap of 1.8 eV. However, in the structure of superstrate type solar cells, interdiffusion have been caused between the buffer layer and the ZCIS layer. In order to suppress the interdiffusion, we have fabricated In2S3/ZCIS substrate type solar cells. The thickness of the interdiffusion region decreased from 70 nm of the superstrate cell to 15 nm of the substrate cell. As a result, the substrate cell with bandgap of 1.8 eV showed VOC of 0.71 V and FF of 0.55 higher than those of the superstrate cells. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-22T05:30:18.33856-05:0
      DOI: 10.1002/pssc.201400313
       
  • Effects of H2S annealing on Cu‐Sn‐S thin films prepared from
           vacuum‐ evaporated Cu‐Sn precursor
    • Authors: Yuji Miyata; Shigeyuki Nakamura, Yoji Akaki
      Abstract: In this work, Cu‐Sn‐S thin films were prepared from a vacuum‐evaporated Cu‐Sn precursor via annealing in H2S from 200 to 500 °C for 1 h. Cu2SnS3 thin films with monoclinic and tetragonal structures were observed by X‐ray diffraction when the annealing temperature exceeded 325 °C. In addition, the SnS phase was observed when the annealing temperature exceeded 275 °C. The surface of the Cu‐Sn‐S thin film annealed at 500 °C was uneven due to the re‐evaporation of SnS. The absorption coefficient of the Cu‐Sn‐S thin films was above 104 cm‐1 with energies above 1.0 eV. The band gap of these films was estimated from transmission and reflection apectra using UV‐visible‐NIR spectrophotometry to be between 0.88‐1.0 eV when the annealing temperature exceeded 450 °C. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-22T05:30:17.372572-05:
      DOI: 10.1002/pssc.201400310
       
  • Temperature dependence of low‐frequency optical phonons in TlInS2
    • Authors: Raul Paucar; YongGu Shim, Kazuki Wakita, Oktay Alekperov, Nazim Mamedov
      Abstract: The unpolarized Stocks component of the Raman spectra of the layered ternary thallium dichalcogenide, TlInS2 was studied with the aid of a Raman confocal microscope system in the low‐frequency region of 35‐150 cm‐1 over the temperature range that embraced the region of the successive phase transitions in this crystal. The observed spectra were deconvoluted into Lorentzian peaks to single‐out the contribution of each Raman mode. The temperature dependence of the Raman frequency and broadening associated with each mode was then obtained. The irregular temperature behaviour of most modes was disclosed in the proximity of phase transitions. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-22T05:30:16.347173-05:
      DOI: 10.1002/pssc.201400350
       
  • RF magnetron sputtering deposition of amorphous Zn–Sn–O thin
           films as a buffer layer for CIS solar cells
    • Authors: Shao‐Wei Chang; Kaoru Ishikawa, Mutsumi Sugiyama
      Abstract: Amorphous Zn–Sn–O (α‐ZTO) layers were deposited by RF magnetron sputtering to provide an alternative n‐type buffer layer for CuInSe2 solar cells. Electrical properties, such as the carrier density, mobility, and resistivity were adjusted by controlling the Sn/(Sn+Zn) ratio of the α‐ZTO layer and by regulating the oxygen partial pressure during sputtering. Valence band discontinuities of α‐ZTO/CuInSe2 were determined using photoelectron yield spectroscopy. The band discontinuity at the interface has “spikes” in the conduction band offset. Further, the short circuit current of a CIGS solar cell that uses an α‐ZTO layer was marginally higher compared to one that used a CdS layer. These results represent a step toward developing a safer, cheaper solar cell with higher performance by using an α‐ZTO film instead of a traditional CdS film. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-21T05:10:30.536287-05:
      DOI: 10.1002/pssc.201400255
       
  • The growth of AgGaTe2 layers on glass substrates with Ag2Te buffer layer
           by closed space sublimation method
    • Authors: Aya Uruno; Ayaka Usui, Yuji Takeda, Tomohiro Inoue, Masakazu Kobayashi
      Abstract: The AgGaTe2 layer growth was performed by the closed space sublimation method on the Mo/glass substrate. The Ag2Te buffer layer was inserted between AgGaTe2 and Mo layers, to improve the quality of grown layers. Crystallographic properties were analyzed by x‐ray diffraction (XRD), and the surface morphologies were analyzed by scanning electron microscopy (SEM). The Ag2Te layer grown on the Mo/glass exhibited a membrane filter structure from the SEM observation. XRD spectra of layers grown with and without the buffer layer were compared. The AgGaTe2 layer with the Ag2Te buffer layer exhibited peaks originating from AgGaTe2, and a very strong diffraction peak of 112 was observed. On the other hand, it was cleared that the layer grown without the buffer layer exhibited no strong peaks associated with AgGaTe2, but Ga‐Te compounds. From this, crystallographic properties of the AgGaTe2 layer were drastically improved by the insertion of the Ag2Te buffer layer. Moreover, the surface morphology exhibited a smooth surface when the Ag2Te buffer layer was inserted. The nucleation site density of AgGaTe2 was probably increased since the membrane filter structure exhibited numbers of kinks at the edge. Chemical reaction between Ga and Mo was also eliminated. It was cleared that the insertion of the buffer layer and its surface morphology were an important parameter to grow high quality AgGaTe2 layers. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-21T05:10:28.403448-05:
      DOI: 10.1002/pssc.201400267
       
  • Study of the synthesis of self‐ assembled tin disulfide
           nanoparticles prepared by a low‐cost process
    • Authors: Arturo Méndez‐López; Arturo Morales‐Acevedo, Yuliana de Jesús Acosta‐Silva, Hironori Katagiri, Yasuhiro Matsumoto, Orlando Zelaya‐Angel, Mauricio Ortega‐López
      Abstract: Oleylamine‐capped tin disulfide nanoparticles were prepared by the hot‐injection method using tin (II) chloride (SnCl2.5H2O) and thioacetamide as tin (II) and sulfur precursors, respectively. The as‐prepared nanoparticles were rinsed with ethanol or toluene, and their structural and morphological were assessed by X‐ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The obtained nanoparticles were single‐phase SnS2 with hexagonal structure. These nanoparticles self‐assembled to produce spherical 40‐50 nm nanostructures after ethanol evaporation, whilst rhombohedral‐shaped nanostructures or round‐edge nanoribbons were produced after the toluene evaporation. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-21T05:10:26.654532-05:
      DOI: 10.1002/pssc.201400271
       
  • Surface etching of CZTS absorber layer by Br‐related solution
    • Authors: H. Miyazaki; M. Aono, H. Kishimura, H. Katagiri
      Abstract: Cu2ZnSnS4 (CZTS) material has many advantages for high‐efficiency thin‐film solar cell absorber layer. A detailed study of the surface of the CZTS and the hetero‐interface of the CZTS/buffer layer is important to improve the conversion efficiency of CZTS thin film solar cells. We investigated the surface condition of the CZTS films by carrying out the surface treatment using bromine solution. The activation energy of the etching using bromine solution was estimated from the slope of the line fitting the graph of the temperature dependence of the etching rate. The activation energy is about 0.35 eV. This value suggests that etching mechanism of CZTS using bromine solution is diffusion‐limited process. There were no significant changes in the structural characteristics after surface treatment by X‐ray diffraction and Raman spectroscopy. From the results of X‐ray photoelectron spectroscopy measurements, a relative surface composition was shifted to Cu‐ and Zn‐rich phase after surface treatment. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-21T05:10:24.804012-05:
      DOI: 10.1002/pssc.201400274
       
  • Effect of surface treatment of CZTS absorber layer by ammonia solution
    • Authors: H. Miyazaki; M. Aono, H. Kishimura, H. Katagiri
      Abstract: In this work, we investigated the effect of surface treatment of the Cu2ZnSnS4 (CZTS) thin films using ammonia solution. CZTS thin films were prepared by RF sputtering using single CZTS target with sulfurization process. In order to study the effect of surface treatment using ammonia solution, solution temperature was varied. Structural properties of the samples are almost same with and without ammonia surface treatment measured by XRD and Raman spectroscopy. From the measurement of the chemical composition, the Zn is dissolved by ammonia solution. In addition, the removal rate of oxygen and sodium is different between deionised water and ammonia solution. Ammonia could have prevented their removal from the surface to solution. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-21T05:10:22.704809-05:
      DOI: 10.1002/pssc.201400275
       
  • Investigation of the sulfurization process of Cu2SnS3 thin films and
           estimation of band offsets of Cu2SnS3‐related solar cell structure
    • Authors: Soichi Sato; Hiroki Sumi, Guannan Shi, Mutsumi Sugiyama
      Abstract: The morphological and structural transition of Cu2SnS3 (CTS) thin films during sulfurization was investigated. The surface morphology and re‐evaporation of CTS films strongly depend on the sulfurization temperature. Low temperature sulfurization enables the films to be sulfurized and form CTS without re‐evaporation. Subsequently, the high‐temperature annealing improves the grain size of the CTS film. In addition, the energy band diagrams of the CTS‐related solar cell structures that use various n‐ type oxide semiconductors, such as CdS, ZnO:In2O3(IZO), ZnO, SnO2, and ZnO:SnO2(ZTO) were examined by photoelectron yield spectroscopy. The band diagrams of IZO/CTS, ZnO/CTS, SnO2/CTS, and ZTO/CTS have a TYPE‐I heterostructure known as a “spike” conduction band offset structure, essential for high‐efficiency solar cells. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-21T05:10:21.237337-05:
      DOI: 10.1002/pssc.201400294
       
  • Improvement of Cu2ZnSn(S,Se)4 solar cell efficiency by surface treatment
    • Authors: Kento Furuta; Noriyuki Sakai, Takuya Kato, Hiroki Sugimoto, Yasuyoshi Kurokawa, Akira Yamada
      Abstract: Surface treatments for the purpose of contamination elimination and surface passivation were performed to as‐deposited CZTSSe thin films before CdS buffer layer deposition. It was found that HCl etching treatment removes contaminations such as sulfide and oxide on CZTSSe surface and helps enhancement of thiourea treatment carried out after HCl etching. Thiourea treatment drastically improves solar cell characteristics, especially FF and JSC, and it would have the effect of surface passivation, although surface sulfuration does not occur. The improvement of characteristics seems to be due to improvement of the film quality and increase in the width of a depletion layer. As a result, conversion efficiency of CZTSSe solar cells was improved from 6.3% to 10.3% with sequential treatment of HCl etching and thiourea treatment. 10.5% was achieved by air anneal after fabrication with both treatments.
      PubDate: 2015-04-21T05:10:19.329902-05:
      DOI: 10.1002/pssc.201400309
       
  • Optical properties and electronic energy‐band structure of Cu2ZnSnS4
    • Authors: Shunji Ozaki; Keiji Hoshina, Yuji Usami
      Abstract: Optical properties of the quaternary Cu2ZnSnS4 semiconductor have been studied by optical absorption, photoluminescence, photoreflectance, and thermoreflectance measurements. Optical absorption measurements suggest that Cu2ZnSnS4 is a direct‐gap semiconductor having the band gap of ∼1.46 eV at 11 K. The photoreflectance and thermoreflectance spectra reveal distinct structures at energies of the critical points in the Brillouin zone. By performing the band‐structure calculation, these critical points are successfully assigned to specific points in the Brillouin zone. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-21T05:10:17.349331-05:
      DOI: 10.1002/pssc.201400254
       
  • Cover Picture: Phys. Status Solidi C 4–5/2015
    • Abstract: GaN based devices with semipolar quantum wells have seen tremendous advances in recent years. Most have been realized homoepitaxially on pseudo bulk substrates which are typically small and expensive. These restrictions of homoepitaxial growth motivate the research for cost‐efficient and large area alternatives. For polar GaN structures, heteroepitaxial growth on sapphire substrates is well established with excellent results – in contrast to the growth of semipolar GaN layers on sapphire, which presents unique challenges. Drawing from expertise in c‐plane samples, Robert A. R. Leute and coworkers (see pp. 376–380) use selective area epitaxy (SAE) on 2‐inch c‐oriented templates to fabricate 3D structures with semipolar side facets. Stripes with triangular cross‐section aligned parallel to GaN a‐direction exhibit {10–11} facets which can be overgrown with quantum wells. By reducing the size of these structures to a sub‐μm scale, they are able to embed their semipolar QWs within planar layers resulting in flat samples with c‐plane surfaces. Thereby all layers except the QWs are grown c‐oriented. The authors present results concerning semipolar QWs emitting in the blue and green spectral range as well as light emitting diodes. The colorized STEM image shows the position of the embedded semipolar QWs inside the otherwise c‐oriented LED structure. The small figures show the spectra of blue and true‐green LED under cw operation and a photograph taken through a microscope during cw operation (image slightly retouched to remove dirt on the surface).
      PubDate: 2015-04-17T03:21:56.468088-05:
      DOI: 10.1002/pssc.201570079
       
  • Cover Picture: Phys. Status Solidi C 4–5/2015
    • Abstract: View of part of the surface during MBE growth of homoepitaxial wurtzite GaN(0001) showing Ga atoms in yellow and N atoms in red. The terrace atoms are already incorporated into the crystal whereas the adatoms diffuse towards step edges. The rate of diffusion of adatoms is a crucial factor in the quality of the crystal. Through DFT calculations, Manjusha Chugh and Madhav Ranganathan on pp. 408–412 have shown that the hopping barrier for an N adatom is reduced from 1.1 eV to 0.7 eV in the presence of a nearby Ga adatom. This explains why small excess Ga can lead to stable growth in MBE. The authors have carried out kinetic Monte Carlo simulations of this process and show the structures formed.
      PubDate: 2015-04-17T03:21:54.136827-05:
      DOI: 10.1002/pssc.201570080
       
  • Issue Information: Phys. Status Solidi C 4–5/2015
    • PubDate: 2015-04-17T03:21:51.104994-05:
      DOI: 10.1002/pssc.201570081
       
  • Semiconducting asphaltene thin films: preparation and characterization
    • Authors: Ibrahim M. Nassar; Zamin Mamiyev, Khuraman Khalilova, Eldar Mammadov, Yegana Aliyeva, Oktay Alekperov, Ayaz Bayramov, Nazim Mamedov
      Abstract: Asphaltene thin films of 100‐500 nm thicknesses were deposited on soda lime glass substrates from toluene solution by spray pyrolysis method. Atomic force microscopy (AFM), photoluminescence (PL), spectroscopic ellipsometry (SE), and electron paramagnetic resonance (EPR) methods were used for characterization of the films. The obtained films were found to be broad band semiconducting material with band gap energy ∼ 3.1 eV and exhibited n‐type conductivity with resistivity ρ ∼ 8·102Ω·cm. Concentration of free radicals and g‐factor were about of ∼ 1018 spin/g and 2.00307, respec­tively. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-14T06:20:10.17852-05:0
      DOI: 10.1002/pssc.201400365
       
  • Minority carrier diffusion length in AlxGa1‐xN (x = 0.1) grown by
           ammonia molecular beam epitaxy
    • Authors: Timur Malin; Alexander Gilinsky, Vladimir Mansurov, Dmitriy Protasov, Eugeny Yakimov, Konstantin Zhuravlev
      Abstract: The room‐temperature minority carrier diffusion length in n ‐Al0.1Ga0.9N grown by ammonia molecular beam epitaxy on (0001) sapphire for photodetector applications has been investigated. The measurements were performed using the spectral dependence of the photocurrent detected by the built‐in p‐n ‐junction on thinner layer samples, and by the electron beam induced current technique on films of up to 2 µm in thickness. The results show that the hole diffusion length in n ‐AlGaN films amounts to 120‐150 nm, which is by 3‐4 times larger than that in GaN films grown under similar growth conditions. The thicker films do not show a considerable improvement in the hole diffusion length value. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-30T02:20:13.593975-05:
      DOI: 10.1002/pssc.201400180
       
  • Power dependence of unusual bands in photoluminescence spectra of
           AlGaN/GaN heterostructures
    • Authors: I. V. Osinnykh; K. S. Zhuravlev, T. V. Malin
      Abstract: AlGaN/GaN heterostructures with a two‐dimensional electron gas (2DEG) grown by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) techniques were investigated by photoluminescence (PL) spectroscopy. Series of PL bands located below the donor bound excitons band have been observed for a high quality MOCVD sample. Two of these PL bands peaked at ħωmax=3.446 and ħωmax=3.423 eV have been observed at both continuous and pulse excitation and connected with the recombination of 2DEG localized at the first and the second levels in the quantum well with free holes. The PL band at ħωmax=3.36 eV may be attributed to recombination of the 2DEG electrons with holes located at acceptors. Band at ħωmax=3.41 eV is not connected with 2DEG because of this band didn’t disappear after etching of the AlGaN layer and this band was observed in all samples. An intensity of all these four PL bands increased superlinearly with rise of the excitation power. The exponents for the Y bands more than 2, while the exponent for the excitonic band is about 1.5 at T=5 K. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-30T02:20:12.751989-05:
      DOI: 10.1002/pssc.201400179
       
  • Effect of reactor pressure on optical and electrical properties of InN
           films grown by high‐pressure chemical vapor deposition
    • Authors: Mustafa Alevli; Nese Gungor, Sabri Alkis, Cagla Ozgit‐Akgun, Inci Donmez, Ali Kemal Okyay, Sampath Gamage, Indika Senevirathna, Nikolaus Dietz, Necmi Biyikli
      Abstract: The influences of reactor pressure on the stoichiometry, free carrier concentration, IR and Hall determined mobility, effective optical band edge, and optical phonon modes of HPCVD grown InN films have been analysed and are reported. The In 3d, and N 1s XPS spectra results revealed In‐N and N‐In bonding states as well as small concentrations of In‐O and N‐O bonds, respectively in all samples. InN layers grown at 1 bar were found to contain metallic indium, suggesting that the incorporation of nitrogen into the InN crystal structure was not efficient. The free carrier concentrations, as determined by Hall measurements, were found to decrease with increasing reactor pressure from 1.61×1021 to 8.87×1019 cm‐3 and the room‐temperature Hall mobility increased with reactor pressure from 21.01 to 155.18 cm2/Vs at 1 and 15 bar reactor pressures, respectively. IR reflectance spectra of all three (1, 8, and 15 bar) InN samples were modelled assuming two distinct layers of InN, having different free carrier concentration, IR mobility, and effective dielectric function values, related to a nucleation/interfacial region at the InN/sapphire, followed by a bulk InN layer. The effective optical band gap has been found to decrease from 1.19 to 0.95 eV with increasing reactor pressure. Improvement of the local structural quality with increasing reactor pressure has been further confirmed by Raman spectroscopy measurements. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-30T02:20:11.55197-05:0
      DOI: 10.1002/pssc.201400171
       
  • The effects of Al on the neutral Mg acceptor impurity in AlxGa1‐xN
    • Authors: U. R. Sunay; M. E. Zvanut, A. A. Allerman
      Abstract: High hole concentrations in AlxGa1‐xN become increasingly difficult to obtain as the concentration of Al increases. It is well known in GaN and related alloys that hole concentration is directly affected by compensation and extended defects. Using electron paramagnetic resonance (EPR) spectroscopy, we studied the amount of neutral Mg in AlxGa1‐xN with x = 0 to 0.28. 0.4‐0.9 μm thick Mg‐doped AlxGa1‐xN films were grown by metal‐organic chemical vapour deposition and annealed at 900 °C anneal in N2. EPR measurements indicate that the amount of neutral Mg decreased by 60% in AlxGa1‐xN films for x = 0.18 and 0.28 as compared to x=0.00 and 0.08. Experiments also showed that the lower neutral Mg for higher Al compositions trend did not depend on threading dislocation densities in the range of 3‐20x109 cm‐2, capping the surface with 5 nm of P+ GaN, or detailed annealing conditions. Additional studies show that oxygen and carbon concentrations are insufficient to account for the decrease in neutral Mg observed in the samples. Although the study cannot isolate the cause for the decrease in neutral Mg, the results clearly demonstrate that the acceptor concentration decreases with increasing Al, providing an additional limitation to achieving high hole densities. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:39.097403-05:
      DOI: 10.1002/pssc.201400184
       
  • Electron paramagnetic resonance studies of bulk Mg‐doped GaN grown
           by high nitrogen pressure solution method
    • Authors: J. Dashdorj; W. R. Willoughby, M. E. Zvanut, M. Bockowski
      Abstract: An acceptor‐related impurity was studied in bulk free standing GaN using electron paramagnetic resonance spectroscopy. Both undoped and Mg‐doped substrates grown by the high nitrogen pressure solution method were examined, but only the doped sample revealed the presence of an EPR‐detected center. Comparison with earlier work on p ‐type GaN films suggests that the defect is an acceptor, heavily compensated during growth. Photo‐EPR studies revealed a photo‐ionization threshold of 2.8 eV, which is interpreted as excitation of an electron from the acceptor to the conduction band. Based on the concentration and photo‐threshold, the EPR center detected in the HNPS doped samples is tentatively identified as Be, which SIMS measurements indicate is a trace impurity in the doped GaN sample. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:37.662444-05:
      DOI: 10.1002/pssc.201400181
       
  • Efficiency of UVA LEDs grown by HVPE in relation with the active region
           thickness
    • Authors: Sergey Kurin; Andrey Antipov, Iosif Barash, Alexander Roenkov, Alexander Usikov, Heikki Helava, Yuri Makarov, Alexander Solomonov, Sergey Tarasov, Anton Evseenkov, Ivan Lamkin
      Abstract: We report on results of the performance study of UVA LEDs depending on the thickness of the active region. UVA LEDs are based on GaN/AlGaN heterostructures grown on Al2O3 (0001) substrates by hydride vapor phase epitaxy (HVPE). It is shown that the use of thick (̴ 100 nm) single layer as the active region of UVA LED is a promising concept to achieve enhanced efficiency. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:36.633618-05:
      DOI: 10.1002/pssc.201400178
       
  • Surface polariton spectroscopy of AlN films grown by ammonia MBE on (0001)
           Al2O3 substrate
    • Authors: N. N. Novikova; E. A. Vinogradov, V. A. Yakovlev, T. V. Malin, V. G. Mansurov, K. S. Zhuravlev
      Abstract: Surface polariton (SP) spectra of nitridated sapphire and rather thick (1 µm) AlN films on sapphire have been measured using attenuated total reflection technique. The high sensitivity of SP allows to see the sapphire spectra change after nitridation of sapphire and even variations parameters of the nitridation procedure. SP dispersion curves depend on degree of conversion of an initial sapphire surface layer into crystalline AlN during the nitridation procedure. The TO frequencies of formed AlN films are higher than the frequency reported for the AlN single crystal indicating the increase of the lattice constant. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:35.669586-05:
      DOI: 10.1002/pssc.201400177
       
  • Blue to true green LEDs with semipolar quantum wells based on GaN
           nanostripes
    • Authors: Robert A. R. Leute; Junjun Wang, Tobias Meisch, Joachim Biskupek, Ute Kaiser, Ferdinand Scholz
      Abstract: Recent advances of the performance of GaN based devices with semipolar quantum wells have been realized homoepitaxially on pseudo bulk substrates which are typically small in size and high in cost. These limitations fuel the search for cheap and large area alternatives. Heteroepitaxial growth on sapphire substrates is well established with excellent results for polar GaN structures ‐ the growth of semipolar gallium nitride on sapphire, however, presents unique challenges. In order to profit from our expertise in c‐plane samples, our semipolar gallium nitride growth experiments are based on growth in c‐direction. Using selective area epitaxy (SAE) on c‐oriented templates, we can grow 3D structures with semipolar side facets. These structures are typically several μm in size which constitutes further challenges for device processing. Reducing the size of the structures to a sub‐μm scale, we are able to bury our semipolar QWs within planar layers resulting in flat samples with c‐plane surfaces. In this contribution, we present our results concerning the structural quality and spectral properties of quantum wells emitting in the blue and green spectral range as well as light emitting diodes. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:33.740958-05:
      DOI: 10.1002/pssc.201400176
       
  • High power blue AlGaInN LED chips with two‐level metallization
    • Authors: D. A. Zakheim; G. V. Itkinson, M. V. Kukushkin, L. K. Markov, O. V. Osipov, A. S. Pavluchenko, I. P. Smirnova, D. A. Bauman
      Abstract: In this paper, we report on the development and fabrication of high power LED chips based on AlGaInN. These chips are meant for flip‐chip mounting and have novel contact pad topology utilizing two‐level metallization with the intermediate dielectric isolation. The size and shape of highly reflective ITO/Ag‐based p‐type and Ti/Ag based n‐type contact pads were adjusted with the use of the numerical simulations of current spreading. As a result, the developed chip has 1 mm2 active area and series resistance as low as 0.3 Ω. The fabricated LEDs demonstrate emission power of 542 mW at 350 mA and the maximum external quantum efficiency equal to 60%. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:32.492114-05:
      DOI: 10.1002/pssc.201400174
       
  • Improved GaN films with low background doping and low deep trap density
           grown by hydride vapor phase epitaxy
    • Authors: Alexander Polyakov; Nikolai Smirnov, Anatoli Govorkov, Elena Kozhukhova, Tatiana Yugova, Alexander Usikov, Heikki Helava, Yuri Makarov
      Abstract: Electrical properties and deep electron and hole traps spectra are compared for undoped n‐GaN films grown by hydride vapor phase epitaxy (HVPE) on sapphire substrates at 850 °C (Group 1) and 950 °C (Group 2). Group 1 samples have very low residual donor concentration ((2‐5)×1014 cm‐3), very low density of electron and hole traps, low leakage current of Schottky diodes. Group 2 samples are not very different from the usual thick HVPE samples in terms of predominant electron and hole traps and MCL spectra. But the concentration of both electron and hole traps is quite high and could contribute to rather high reverse leakage current, low photocurrent and pronounced tunneling. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:31.266409-05:
      DOI: 10.1002/pssc.201400173
       
  • Simulation of the stress state of GaN‐AlN based epitaxial devices
    • Authors: Arun Kumar; Ganesh Iyer, Anandh Subramaniam
      Abstract: The stress state plays an important role in the performance of GaN‐AlN based multilayer epitaxial devices and their degradation with time. The stress state arises due to the superposition of stresses originating from multiple sources: (i) thermal mismatch, (ii) epitaxial growth, (iii) low angle grain boundaries (threading dislocations) and (iv) interfacial misfit edge dislocations. The current investigation pertains to the plane strain linear elastic finite element simulation of the stress state of a model GaN‐AlN high electron mobility transistor (HEMT) device on a Si substrate, taking into account the above‐mentioned sources of stresses. The value of stresses arising from grain boundary dislocations corresponds to the experimental results and imposed as tractions in the numerical model, while the other stresses are modelled using eigenstrains in appropriate regions in the finite element domain. A ten step simulation strategy is developed to simulate the stress state of the entire HEMT device. It is seen that: (i) the AlN layers are under tensile stress, (ii) the embedded GaN layers are under compressive stress, (iii) the GaN layer between source and drain is under tensile stress, (iv) the AlGaN layer is under tensile stress, (v) the source and the drain are mostly in tensile stress, while the gate is nearly stress‐free. The AlGaN and GaN layers (close to the source and drain) are under tensile stress (by considerations of pure epitaxy these are expected to be under compression). The critical thickness for the stability of a misfit edge dislocation at the AlN‐GaN interface is computed using the simulations. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:29.757345-05:
      DOI: 10.1002/pssc.201400170
       
  • 2D AlN crystal phase formation on (0001) Al2O3 surface by ammonia MBE
    • Authors: Timur Malin; Vladimir Mansurov, Yury Galitsyn, Konstantin Zhuravlev
      Abstract: Kinetics of a two‐dimensional (2D) AlN layer formation on (0001) sapphire (Al2O3) surface during nitridation at different ammonia fluxes is investigated by reflection high energy electron diffraction (RHEED). The process on the surface is described in the framework of a chemical reactions kinetic model including interaction between partially reduced aluminum oxide species (AlO) and chemisorbed NH2 particles. The experimentally determined AlN formation rates as functions of both the temperature and the ammonia pressure are successfully described by a simple set of kinetic equations. Calculated maximum rate of the process well agrees with the experimental values. Precision measurement of 2D AlN lattice parameters during the nitridation process detects the value of 3.01 Å. This value coincides exactly with a characteristic structure parameter of the oxygen‐deficient Al2O3 surface. We assume this coincidence results from flexibility of the 2D AlN monolayer which provides minimization of elastic stresses at the AlN/(0001)Al2O3 interface. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:28.350806-05:
      DOI: 10.1002/pssc.201400168
       
  • Contents: Phys. Status Solidi C 4–5/2015
    • Pages: 327 - 330
      PubDate: 2015-04-17T03:21:54.027087-05:
      DOI: 10.1002/pssc.201570082
       
  • Growth of III‐Nitrides
    • Authors: Russell D. Dupuis; Fernando A. Ponce
      Pages: 331 - 333
      Abstract: The International Symposium on the Growth of III‐Nitrides (ISGN) series of conferences have been premier international forums for experts from academia, industry, and national laboratories to present their latest progress and exchange ideas in the fundamental and applied aspects of III‐N bulk and epitaxial growth technologies as well as related device advances. III‐N compound semiconductor materials underlie many of today's most advanced high‐performance devices such as LEDs, laser diodes, and transistors, which are becoming an essential part of the solution of many global problems. In the future, III‐N solar cells, nanostructure materials, and other innovative devices will play a similar significant role in improving the human condition. The primary purpose of ISGN‐5 was to foster the continued advance of this important field of research and development. The ISGN‐5 was organized by a team of US‐based experts in the field and the choice of Plenary and Invited speakers was based upon inputs from the International Advisory Committee composed of active III‐N researchers from all over the world. We actively solicited papers describing the latest work in the following technical areas: – III‐N bulk growth: AlN, GaN, InN – Epitaxial growth techniques – Ternary and quaternary alloys – III‐N nanostructures – Defect control and surface effects – Optical and electrical properties – III‐N magnetic and spin‐related phenomena – III‐N devices: FETs, HBTs, rectifiers, LEDs, lasers, photodetectors, and novel devices The ISGN‐5 program had fourteen regular sessions and two poster sessions scheduled over four days. The total number of attendees was 146. The conference technical sessions began with a plenary talk by André Strittmatter who described the current state‐of‐the‐art of GaN on Si. The regular sessions were begun with Invited Speakers. The full conference schedule is available here: http://www.mrs.org/isgn‐5‐program/. The primary conference support was provided by AIXTRON, Sandia National Laboratories, the U.S. National Science Foundation, and the U.S. Army Research Office. We were fortunate to have the on‐site support of eleven commercial vendors of equipment and services related to III‐N materials and devices who arranged to have a booth at ISGN‐5 to display and demonstrate their products. These companies included AIXTRON, Aymont Technology Inc., Evans Analytical Group, HexaTech, Inc., k‐Space Associates, Inc., KITZ SCT America Corporation, Nitride Crystals, Inc., Proton OnSite, Riber, Inc., Semiconductor Technology Research–STR Group, and Taiyo Nippon Sanso Corporation. The ISNG‐5 proceedings Guest Editors were Christian Wetzel (Rensselaer), Jae‐Hyun Ryou (University of Houston), and Michael Manfra (Purdue University). We thank the sponsors, the exhibitors, the Materials Research Society staff, the members of the Conference Organizing Committee, the members of the International Advisory Committee and of the Program Committee, and everyone who attended for their support. The ISGN‐5 Symposium Chairs, Russell D. Dupuis, Georgia Institute of Technology Fernando A. Ponce, Arizona State University
      PubDate: 2015-04-17T03:21:52.749639-05:
      DOI: 10.1002/pssc.201570083
       
  • HVPE homoepitaxy on freestanding AlN substrate with trench pattern
    • Authors: Yoshinobu Watanabe; Hideto Miyake, Kazumasa Hiramatsu, Yosuke Iwasaki, Shunro Nagata
      Pages: 334 - 337
      Abstract: Conditions on chemical surface treatment and thermal treatment of sublimation‐freestanding AlN substrates were investigated to remove damage layers on surfaces for high‐quality and crack‐free AlN films grown by hydride vapour phase epitaxy (HVPE). By wet etching, the residue on the surface was removed and the polishing scratches were reduced. Atomic steps were formed on the surface by the subsequent thermal treatment at 1450 °C for 10 min, and surface layer of 220 nm in thickness was removed, Homoepitaxial growth on freestanding AlN substrate with trench pattern was also performed. A crack‐free AlN film with atomic steps was obtained on the trench‐patterned bulk AlN substrate, and the emission at the band edge near 206.9 nm was dominant. The wavelength of luminescence from cross‐sectional and surface of the HVPE‐AlN layer was maintained. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-01-23T08:10:48.179394-05:
      DOI: 10.1002/pssc.201400202
       
  • Modeling micromechanical response to thermal history in bulk grown
           aluminum nitride
    • Authors: Payman Karvani; Antoinette M. Maniatty
      Pages: 345 - 348
      Abstract: A thermal‐elastic‐viscoplastic model suitable for modeling aluminum nitride (AlN) during crystal growth is presented. A crystal plasticity model that considers slip along crystallographic slip systems and the evolution of mobile and immobile dislocations on the prismatic and basal slip systems is developed. The model has been implemented into a finite element framework, and a sublimation growth process is modeled to demonstrate the model capability. The dislocation density, which characterizes the crystal quality, and the maximum tensile stress on the cleavage planes (m ‐planes), which leads to cracking, are computed. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-04-17T03:21:53.01423-05:0
      DOI: 10.1002/pssc.201400189
       
  • Degradation of external quantum efficiency of AlGaN UV LEDs grown by
           hydride vapor phase epitaxy
    • Authors: Natalia Shmidt; Alexander Usikov, Eugenia Shabunina, Anton Chernyakov, Alexey Sakharov, Sergey Kurin, Andrei Antipov, Iosif Barash, Alexander Roenkov, Heikki Helava, Yuri Makarov
      Pages: 349 - 352
      Abstract: A comparative study of the degradation of HVPE‐grown 360 nm AlGaN/GaN UV and commercially available InGaN/GaN blue LED chips was performed. The common feature of the degradation of these two types of LEDs was found to be the increase of the conductivity of shunt paths under current injection. The paths (shunts) are localized in the extended defects system (EDS). It is proposed that the conductivity increase is due to defect formation under multiphonon carriers recombination in a part of the EDS enriched by Ga or In atoms. This process is accompanied by a local overheating and migration of Ga or In atoms. To increase the lifetime of the AlGaN/GaN UV LEDs to more than 2000 h it is necessary to improve their nano‐structural and nanoscale AlGaN composition ordering. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-01-23T08:10:46.189625-05:
      DOI: 10.1002/pssc.201400172
       
  • Time‐resolved photoluminescence characterization of 2 eV band in AlN
    • Authors: Ivan A. Aleksandrov; Vladimir G. Mansurov, Victor F. Plyusnin, Konstantin S. Zhuravlev
      Pages: 353 - 356
      Abstract: We report time‐resolved and temperature‐dependent photoluminescence investigations of 2 eV photoluminescence band in AlN with below bandgap excitation. Series of the samples grown by molecular beam epitaxy on sapphire substrates with varying growth conditions have been studied. Intensity of the 2 eV photoluminescence band has been found to increase with increasing III/V flux ratio. The 2 eV photoluminescence band has been described in one‐dimensional configuration coordinate model. A possible origin of this orange emission has been discussed. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-01-23T08:10:47.139747-05:
      DOI: 10.1002/pssc.201400175
       
  • Fabrication of AlGaN multiple quantum wells on sapphire with
           lattice‐relaxation layer
    • Authors: Kazuhiro Nakahama; Fumitsugu Fukuyo, Hideto Miyake, Kazumasa Hiramatsu, Harumasa Yoshida, Yuji Kobayashi
      Pages: 361 - 364
      Abstract: The influences of three types of lattice‐relaxation layer between AlGaN multiple quantum wells (MQWs) and AlN layer on sapphire substrate were investigated. For structure (a), two‐high‐Al‐mole‐fraction AlGaN layers grown at 1170 °C was prepared. For structure (b), an AlN interlayer with growth temperature at 1450 °C was inserted between AlN/sapphire substrate and two‐high‐Al‐mole‐fraction AlGaN layer. For structure (c), an Al‐composition‐graded AlGaN layer with decreasing Al composition was grown after an AlN interlayer at 1450 °C by lowering the temperature gradually from the growth temperature of AlN. The narrowest rocking curve X‐ray diffraction at AlGaN MQWs occurs while using structure (b) as lattice‐relaxation layer. The highest emission intensity of cathodoluminescence from AlGaN MQWs at room temperature was also shown by using structure (b). The ratio of integrated intensity of spectra at 300 K and 10 K (I300K/I10K) is 58%. High temperature AlN films as lattice‐relaxation layer improved the crystal quality and emission intensity in AlGaN MQWs. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:20.654157-05:
      DOI: 10.1002/pssc.201400201
       
  • Study of interference effects on the photoluminescence of AlGaN/GaN
           quantum wells
    • Authors: M. Ramírez‐López; Y. L. Casallas‐Moreno, M. Pérez‐Caro, A. Escobosa‐Echevarria, S. Gallardo‐Hernández, J. Huerta‐Ruelas, M. Lopez‐Lopez
      Pages: 365 - 368
      Abstract: In this work we compared the optical properties of AlGaN(50 nm)/GaN(5 nm) quantum wells (QWs) grown by plasma‐assisted molecular beam epitaxy (PAMBE) technique, on Si(111) substrates and sapphire substrates. Optical properties were acquired by photoluminescence (PL) and reflectance (R) spectroscopies. Reflectance spectra shows interference oscillations of the reflected beam at Air/AlGaN and the beam reflected at bottom interface with Si substrate. Such oscillations vanish at the band gap of GaN buffer layer (3.4 eV). The PL spectra of samples grown on Silicon substrate shows a photoluminescence modulation effect, attributed to interference of light emitted from the QWs that is reflected at different heterostructure interfaces. On sapphire substrate no modulation effect is present. This could be explained due to interfacial roughness and the smaller refractive index of sapphire in comparison to silicon. PL shows a strong emission around 3 eV, which is in agreement with recombination energy determined by self‐consistent calculations, which consider a 4 MV/cm built‐in electric field and low carrier densities. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:25.077187-05:
      DOI: 10.1002/pssc.201400185
       
  • Reflectance analysis on the MOCVD growth of AlN on Si(111) by the virtual
           interface model
    • Authors: Tuoh‐Bin Ng; David A. Ewoldt, Debra A. Shepherd, Mark J. Loboda
      Pages: 385 - 388
      Abstract: The reflectance‐time profile of AlN‐on‐Si(111) growth by MOCVD as acquired through an in‐situ optical reflectance monitor is analyzed. It is found that, similar to the case of GaN‐on‐sapphire nucleation and growth through the low temperature GaN or AlN buffer layer techniques, the reflectance profile for AlN‐on‐Si also contains information that relate to the growth mechanism, which can then be correlated to the as‐grown material quality. Based on the equations for the Virtual Interface model, a set of 6 parameters can be used to curve‐fit the reflectance traces of AlN growth as acquired by the in‐situ optical monitor. By analyzing a range of 405 nm AlN reflectance‐time data from single layer AlN growth to multilayer AlN/AlGaN/GaN stack grown on Si(111), the “goodness of fit” statistics are found to correlate with material quality metrics such as the XRD (002) rocking curve FWHM for AlN, microscopic morphological roughness of the AlN surface, as well as the resultant wafer bow and curvature for GaN/AlGaN grown on the AlN/Si(111) substrate. The correlations provide useful insight into the desirable mechanism and growth mode for the high temperature MOCVD growth of AlN and GaN on Si(111). When fully established, the technique has the potential of being used as an in‐situ pass/fail screen for the MOCVD growth of GaN‐on‐Si. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-01-23T08:10:41.27289-05:0
      DOI: 10.1002/pssc.201400159
       
  • A numerical analysis of a MOCVD process for the growth of GaN nanowires
           using GaCl3 and NH3
    • Authors: Edgar Serrano Perez; Miguel A. Nuñez Velazquez, Fernando Juárez Lopez
      Pages: 389 - 393
      Abstract: In this paper, the analysis of horizontal cold wall reactor for GaN nanowires growing from GaCl3 and NH3 at atmospheric pressure conditions has been studied. It aims to provide better understanding of the MOCVD process especially of deposition process of GaN nanowires as well as fluid dynamics inside the reactor. Numerical solution to transport model coupled with 2D geometry using CFD shows several results including GaCl3 thermal decomposition at different temperature conditions, velocity and temperature distribution as well as concentration profiles into reactor. Afterwards experimental parameters of temperature and gases flow were set to growth of GaN nanowires. Scanning electron microscopy analysis shows the microstructural characteristics of GaN nanowires. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T06:50:42.903471-05:
      DOI: 10.1002/pssc.201400165
       
  • Low‐temperature hollow cathode plasma‐assisted atomic layer
           
    • Authors: Cagla Ozgit‐Akgun; Eda Goldenberg, Sami Bolat, Burak Tekcan, Fatma Kayaci, Tamer Uyar, Ali Kemal Okyay, Necmi Biyikli
      Pages: 394 - 398
      Abstract: Hollow cathode plasma‐assisted atomic layer deposition (HCPA‐ALD) is a promising technique for obtaining III‐nitride thin films with low impurity concentrations at low temperatures. Here we report our previous and current efforts on the development of HCPA‐ALD processes for III‐nitrides together with the properties of resulting thin films and nanostructures. The content further includes nylon 6,6‐GaN core‐shell nanofibers, proof‐of‐concept thin film transistors and UV photodetectors fabricated using HCPA‐ALD‐grown GaN layers, as well as InN thin films deposited by HCPA‐ALD using cyclopentadienyl indium and trimethylindium precursors. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:26.998226-05:
      DOI: 10.1002/pssc.201400167
       
  • SCM and SIMS investigations of unintentional doping in III‐nitrides
    • Authors: M. J. Kappers; T. Zhu, S.‐L. Sahonta, C. J. Humphreys, R. A. Oliver
      Pages: 403 - 407
      Abstract: Cross‐sectional scanning capacitance microscopy measurements of unintentionally doped model structures for InGaN quantum wells, GaN barriers and AlInN electron‐blocking layers showed n ‐type conductivity for the In‐containing layers. Secondary ion mass spectrometry indicated that oxygen impurities are the likely source of the electron density in the model layers. The n ‐type conductivity as well as the oxygen impurity level increases to ∼1018 cm‐3 for AlInN lattice‐matched to GaN. These results suggest that the background electron concentration due to oxygen impurities in indium‐containing layers needs to be considered in the design and theoretical modelling of device structures. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:19.646276-05:
      DOI: 10.1002/pssc.201400206
       
  • Kinetic Monte Carlo simulations of epitaxial growth of wurtzite GaN(0001)
    • Authors: Manjusha Chugh; Madhav Ranganathan
      Pages: 408 - 412
      Abstract: A lattice based kinetic Monte Carlo (kMC) simulation is developed to describe growth of GaN(0001) in conditions typical of a molecular beam epitaxy unit. Deposition and surface diffusion via attachment and detachment of atoms are the main processes considered in this model. The energy barriers for surface diffusion are estimated from ab‐initio density functional theory calculations. From the ab‐initio calculations, we identify a rapid motion of N atoms attached to Ga adatoms. Preliminary kMC simulation results indicate that this motion allows N adatoms to move towards their preferred positions and thereby facilitate smooth growth prior to the formation of the protective Ga adlayer which is believed to promote smooth growth under Ga rich conditions. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:21.798767-05:
      DOI: 10.1002/pssc.201400194
       
  • Improved thermal stability and narrowed line width of photoluminescence
           from InGaN nanorod by ytterbium doping
    • Authors: Jingzhou Wang; Kiran Dasari, Kevin Cooper, Venkata R. Thota, Jason Wright, Ratnakar Palai, David C. Ingram, Eric A. Stinaff, S. Kaya, W. M. Jadwisienczak
      Pages: 413 - 417
      Abstract: Nanorod of in situ Yb‐doped InGaN and undoped InGaN have been grown on (0001) sapphire substrates by plasma assisted molecular beam epitaxy (MBE). Selected regions on Yb‐doped InGaN sample show single dominant near band edge emission (NBE) in green, yellow or orange color due to the variation of In content. Temperature dependent PL peak energy of InGaN nanorod shows the characteristic S ‐shaped behavior indicating the presents of strong exciton localization energy in undoped InGaN nanorod. The exciton localization energy reduced significantly after incorporating Yb into InGaN, giving rise to damping of the S‐shape profile amplitude and narrowing of the PL line width from ∼20 meV to ∼12 meV at 11 K. It is proposed that the improved PL thermal stability and the PL line width in Yb‐doped InGaN nanorod is affected by the Yb gettering effect. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T08:10:24.031155-05:
      DOI: 10.1002/pssc.201400186
       
  • Investigation of stress, defect structure and electrical conduction in
           large diameter III‐nitride epitaxy on silicon substrates
    • Authors: G. Chung; M. J. Loboda, E. Carlson, D. Ewoldt, T. Ng, D. Shepherd
      Pages: 418 - 422
      Abstract: The results of studies focused on understanding materials‐electrical correlations for GaN‐based films deposited on 150 mm diameter Si wafers in a batch MOCVD system are reported. A wide range of film stress and electrical conduction is observed at consistent and good X‐ray FWHM values. The vertical leakage currents show a strong asymmetry on the polarity of the bias voltage. Film stress (wafer bow) and impurity variations in the buffer layers show no correlation with leakage currents. Surface pit formation and conductive interfaces are critical to determine the leakage currents in buffer layers. TEM image confirms that surface pit stems from voids in Si substrate. The vertical leakage currents follow the Frenkel‐Poole conduction model at the trap energy of 0.7 eV. Vertical leakage currents measured in films can be reduced by a novel, post‐growth process. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-03-18T06:50:41.884366-05:
      DOI: 10.1002/pssc.201400137
       
  • Unusual phonon mode behaviour in zinc‐blende BN/GaN superlattices
    • Authors: Devki N. Talwar; Andrew F. Zhou, Tzuen‐Rong Yang
      Pages: 430 - 433
      Abstract: Comprehensive calculations of the long‐wavelength optical phonons are reported for zinc‐blende BN films by exploiting a linear response theory to simulate far‐infrared reflectivity and transmission spectra at oblique incidence. A rigid‐ion‐model is used to study the lattice dynamics of the unconventional BN/GaN short‐period superlattices (SLs). Besides empathizing, the anisotropic mode behaviour of optical phonons, the study has offered evidence of acoustic‐mode anti‐crossing, mini‐gap formation, confinement, as well as BN‐like modes falling between the gap regions separating the optical phonons of the two bulk (BN, GaN) semiconductor materials. A bond‐polarizability approach within the second‐nearest‐neighbour linear‐chain model is also employed to visualize the Raman intensity profiles of the short‐period BN/GaN SLs, revealing major trends of the phonon characteristics noted in many conventional SLs, while eliciting some interesting contrasts. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-01-23T08:10:45.055269-05:
      DOI: 10.1002/pssc.201400157
       
  • Plasma‐assisted molecular beam epitaxy of strain‐compensated
           a‐plane InGaN/AlGaN superlattices
    • Authors: Ryan W. Enck; N. Woodward, C. Gallinat, G. Metcalfe, A. V. Sampath, H. Shen, M. Wraback
      Pages: 434 - 438
      Abstract: Strain‐compensated InGaN/AlGaN structures can enable the growth of thick layers of InGaN epitaxial films far beyond the critical thickness for InGaN grown pseudomorphically to GaN. In this paper, we demonstrate the epitaxial growth of high‐quality strain‐compensated a‐plane In0.12Ga0.88N/Al0.19Ga0.81N superlattices up to 5 times thicker than the critical thickness on free‐standing a‐plane GaN substrates by plasma‐assisted molecular beam epitaxy (PA‐MBE). The superlattices consist of 50 to 200 periods of 10 nm thick In0.12Ga0.88N and 6 nm thick Al0.19Ga0.81N layers. The structures are characterized using a double crystal X‐ray diffractometer, asymmetric reciprocal space mapping, and atomic force microscopy. We use X‐ray diffraction to determine the strain, composition, degree of relaxation, and superlattice period of our samples. The structural characteristics of periodic structures containing from 50 to 200 periods are compared to single layer, uncompensated In0.12Ga0.88N films. A 100 period structure exhibited only 15% relaxation compared to 69% relaxation for the bulk In0.12Ga0.88N film grown with the same total InGaN thickness but without strain‐compensating layers. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-01-23T08:10:49.21007-05:0
      DOI: 10.1002/pssc.201400208
       
  • Challenges for Group III Nitride Semiconductors for Solid State Lighting
           and Beyond
    • Pages: 451 - 451
      PubDate: 2015-04-17T03:21:51.545713-05:
      DOI: 10.1002/pssc.201570084
       
  • Investigation of cubic GaN quantum dots grown by the
           Stranski‐Krastanov process
    • Authors: M. Bürger; J. K. N. Lindner, D. Reuter, D. J. As
      Pages: 452 - 455
      Abstract: We investigate the formation of cubic GaN quantum dots (QDs) on pseudomorphic strained cubic AlN layers on 3C‐SiC (001) substrates grown by means of molecular beam epitaxy. Surface morphologies of various QD sizes and densities were obtained from uncapped samples by atomic force microscopy. These results were correlated with similar but capped samples by photoluminescence experiments. The QD density varies by one order of magnitude from ∼1x1010 cm‐2 to ∼1x1011 cm‐2 as a function of the GaN coverage on the surface. The initial layer thickness for the creation of cubic GaN QDs on cubic AlN was obtained to 1.95 monolayers by a comparison between the experimental results and an analytical model. Our results reveal the strain‐driven Stranski‐Krastanov growth mode as the main formation process of the cubic GaN QDs. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-02-12T07:40:17.990154-05:
      DOI: 10.1002/pssc.201400132
       
  • Designing InGaN/GaN nano‐LED arrays for étendue‐limited
           applications
    • Authors: Sophia Fox; Simon O'Kane, Szymon Lis, Duncan Allsopp
      Pages: 456 - 459
      Abstract: This paper presents the far field results of a study by simulation using the finite‐difference time‐domain (FDTD) method of vertical light emitting diode structures with an incorporated ordered nanorod array in place of the typical surface roughened region. For a dipole placed directly below the centre nanorod in the FDTD model, highly collimated light is achieved by changing the radii of the nanorods, for a fixed array pitch, which we attribute mainly to Bragg diffraction. By changing the pitch only, higher diffraction orders are observed in the far field emission as the pitch is increased and a relative increase in the directionality of emission is predicted. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-02-12T07:40:19.018773-05:
      DOI: 10.1002/pssc.201400240
       
  • Computational model of 2DEG mobility in AlGaN/GaN heterostructures
    • Authors: Karine Abgaryan; Ilya Mutigullin, Dmitry Reviznikov
      Pages: 460 - 465
      Abstract: The computational scheme of multiscale modeling of semiconductor heterostructures is presented. Three scale levels are taken into account. On the atomic level the system is described using crystallographic information and quantum‐mechanical model. Ab initio modeling allows to determine the electronic structure, define polarization effects and calculate charge densities on the interfaces between layers. Obtained information is used in the nanoscale level model for the calculation of the charge carrier distribution in the heterostructure. At this level mathematical model contains the system of conjugated Schrödinger and Poisson equations. The carrier density distributions over the lateral direction of the multilayered structure and 2DEG localization are of the most interest at this point. This data is used in the next scale level model where electron mobility is calculated. A wide range of electron scattering mechanisms are taken into account during this calculation. This approach was applied to model 2DEG in AlGaN/AlN/GaN heterostructures. The good agreement between calculated values of interface charge density, 2DEG electron concentration, electron mobility and known experimental data was achieved. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-02-27T05:50:54.13433-05:0
      DOI: 10.1002/pssc.201400200
       
  • The temperature dependence of the luminescence of
           rare‐earth‐doped semiconductors: 25 years after Favennec
    • Authors: K. P. O'Donnell
      Pages: 466 - 468
      Abstract: Twentyfive years after the publication of P. N. Favennec's seminal paper on luminescence from rare‐earth‐doped semiconductors (Electron. Lett. 25, 718–719 (1989), with 390+ citations to date) we examine the long shadow it has cast on recent studies of europium‐doped GaN, aimed at substituting for InN‐rich InGaN in red‐light‐emitting devices (LEDs). According to Favennec's principle, wider band gap semiconductors should show weaker thermal quenching, thus favouring the III‐nitrides hugely. The conventional approach to fitting temperature dependences of light emission, based on competition between radiative and non‐radiative transitions, is presented here in simplified form and an alternative fitting equation proposed. The original data of Favennec (op. cit.) is re‐examined in the light of these fitting models. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-02-27T05:50:52.467273-05:
      DOI: 10.1002/pssc.201400133
       
  • STEM‐CL investigations on the influence of stacking faults on the
           optical emission of cubic GaN epilayers and cubic GaN/AlN
           multi‐quantum wells
    • Authors: R. M. Kemper; P. Veit, C. Mietze, A. Dempewolf, T. Wecker, F. Bertram, J. Christen, J. K. N. Lindner, D. J. As
      Pages: 469 - 472
      Abstract: We report the influence of {111} stacking faults on the cathodoluminescence (CL) emission characteristics of cubic GaN (c‐GaN) films and cubic GaN/AlN multi‐quantum wells. Transmission electron microscopy (TEM) measurements indicate that stacking faults (SFs) on the {111} planes are the predominant crystallographic defects in epitaxial films, which were grown on 3C‐SiC/Si (001) substrates by plasma‐assisted molecular beam epitaxy. The correlation of the SFs and the luminescence output is evidenced with a CL setup integrated in a scanning TEM (STEM). By comparing the STEM images and the simultaneously measured CL signals it is demonstrated that SFs in these films lead to a reduced CL emission intensity. Furthermore, the CL emission intensity is shown to increase with increasing film thickness and decreasing SF density. This correlation can be connected to the reduction of the full width at half maximum of X‐ray diffraction rocking curves with increasing film thickness of c‐GaN films. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2015-02-27T06:10:12.359989-05:
      DOI: 10.1002/pssc.201400154
       
  • Erratum: Influence of annealing on the properties of (Cd,Mn)Te crystals
    • Authors: M. Witkowska‐Baran; D. M. Kochanowska, A. Mycielski, R. Jakieła, A. Wittlin, W. Knoff, A. Suchocki, P. Nowa‐kowski, K. Korona
      Pages: 473 - 473
      Abstract: The authors have completed their institutions to properly reflect the contributions of the affiliated institutions.
      PubDate: 2015-04-17T03:21:55.561107-05:
      DOI: 10.1002/pssc.201570085
       
 
 
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