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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  [1598 journals]
  • Effects of substrate temperature on change in percolation properties of
           ultra thin dielectric films
    • Abstract: In this paper, we explored the impact of surface roughness on ultra‐thin dielectrics characteristics. Simple cubic lattice is used as a base for depositing spheres of radius R, designed as a thin film, as the base for simulation of defects generation and deposition. Continuum percolation model, used to generate a rough surface in order to analyse how roughness and temperature influence the conductivity, consists of randomly placed spheres of either one or some distribution of radii, which then form a thin, rough layer in question. It is shown that when the temperature of the substrate is increased material defects tend to form within the film contributing to a faster cluster growth and greater film conductivity. The influence of temperature on average cluster size for homogeneous distribution of defects is assumed according to the applied temperature (depending on the free carrier's diffusion length) is researched. It is evident from the performed simulations that temperature has an important influence on thin film conductivity in several different ways; it can contribute to the increase of the number of spanning clusters or the average size of clusters. This way, defects can either provide starting points for new spanning clusters or can encourage clusters merging. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-06-03T03:10:10.670256-05:
      DOI: 10.1002/pssc.201610041
       
  • Deposition of a‐Si:H thin films using tailored voltage waveform
           plasmas: impact on microstructure and stability
    • Authors: Junkang Wang; Christophe Longeaud, Federico Ventosinos, Dmitri Daineka, Mustapha El Yaakoubi, Erik V. Johnson
      Abstract: Exciting processing plasmas using non‐sinusoidal, “Tailored” voltage waveforms (TVWs), have recently been shown to be effective to separately control the maximum ion bombardment energy (IBE) and the ion flux on each electrode in the capacitively coupled plasma (RF‐CCP) processes. In this work, we use it to deposit hydrogenated amorphous silicon (a‐Si:H) thin films from hydrogen‐diluted silane by low temperature plasma‐enhanced chemical vapor deposition. The impact of using TVWs on the material's structural and electronic properties is examined. Excessively low IBE can lead to a high Si‐H2bonded hydrogen content within the deposited films, which results in a deterioration of the material stability upon light‐soaking, detectable at a microstructure level. A low content of hydrogen bonded in a Si‐H2configuration and a low sub‐gap density of states was observed in the film deposited using a “sawtooth‐down” type of waveform. Such excitation also produced the a‐Si:H films with the best transport properties (majority and minority carrier μτ‐products and the ambipolar diffusion length) and stability under light‐soaking. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-06-03T03:10:09.73298-05:0
      DOI: 10.1002/pssc.201600024
       
  • Jan Vanhellemont – 35 years of materials research in
           microelectronics
    • Abstract: On the occasion of the decease of Prof. Jan Vanhellemont, a brief overview of his scientific career, covering more than 35 years in semiconductor materials science, is given in this paper. The main scientific highlights are summarized. Besides the different positions he has taken in his career at different universities and companies, he has also been very active in establishing a world‐wide network of collaborations and contacts, who often became also good friends. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-06-03T03:10:08.529745-05:
      DOI: 10.1002/pssc.201600023
       
  • High performance InGaZnO‐based Schottky diodes fabricated at room
           temperature
    • Authors: Linlong Yan; Qian Xin, Lulu Du, Jiawei Zhang, Yi Luo, Qingpu Wang, Aimin Song
      Abstract: Recently, Indium gallium zinc oxide (InGaZnO or IGZO) has attracted much attention for flexible and transparent electronics, because of its superior electric properties, optical transparency and low processing temperature. In this work, Schottky diodes with a structure of Pd/IGZO/Ti/Au were fabricated by radio‐frequency magnetron sputtering at room temperature without any thermal treatment. The optimised diode with a 66‐nm‐IGZO layer shows an extremely large barrier height (1.02 eV), a very high rectification ratio (> 8.5 × 107), and a close to unit ideality factor (1.23). Our results suggest that Pd and IGZO can form very high quality Schottky contact with a large barrier height, extremely low defects density and high uniformity. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-06-03T03:10:07.432455-05:
      DOI: 10.1002/pssc.201510291
       
  • Cover Picture: Phys. Status Solidi C 5–6/2016
    • Abstract: The paper of Bowen Song and coworkers on pp. 195–199 and the cover image address the growth mode of nitride semiconductors by molecular beam epitaxy (MBE) on nano‐patterned (0001) sapphire substrates. During the initial stages of growth the pillars of the patterned substrate act as seeds leading to fully faceted nitride films grown along the [0001] direction. As the film grows to more than 3 μm, the growth is dominated by the lateral growth of the top (0001) facets, since the flux of arriving precursors is higher in these facets than in the inclined ones. The coalescence of these hexagonal (0001) facets leads to films with smooth surface morphology. In this growth mode, threading dislocations, propagating along the [0001] direction during the initial stages of growth, have the potential to be redirected by the inclined facets leading to their annihilation. Thus, nitride films thicker than 3 μm, grown on nano‐patterned substrates are expected to have fewer threading defects and better optoelectronic properties. This growth mode may be applicable to other families of materials grown on nano‐patterned substrates.
      PubDate: 2016-05-25T02:24:53.470375-05:
      DOI: 10.1002/pssc.201670123
       
  • Issue Information: Phys. Status Solidi C 5–6/2016
    • PubDate: 2016-05-25T02:24:49.56996-05:0
      DOI: 10.1002/pssc.201670124
       
  • HgCdTe p+‐n structures grown by MBE on Si (013) substrates for high
           operating temperature SWIR detectors
    • Authors: V. M. Bazovkin; S. A. Dvoretskiy, A. A. Guzev, A. P. Kovchavtsev, D. V. Marin, Z. V. Panova, I. V. Sabinina, Yu. G. Sidorov, G. Yu. Sidorov, A. V. Tsarenko, V. S. Varavin, V. V. Vasiliev, M. V. Yakushev
      Abstract: Electrophysical properties of multilayered heteroepitaxial structures of Hg1‐xCdxTe with x=0.3‐0.4 grown by molecular beam epitaxy on silicon substrates are presented. The passivating effect of thin CdTe layers grown on top of the structures in single process is demonstrated. Comparison between experimental and theoretical temperature dependencies of reverse currents in n‐on‐p and p‐on‐n diodes fabricated by boron and arsenic ion implantation in vacancy‐doped p‐type and In‐doped n‐type Hg1‐xCdxTe films, respectively, are presented. The influence of p‐n junction position in double‐layer heterostructure on temperature dependencies of reverse currents is examined. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-05-13T06:30:15.827321-05:
      DOI: 10.1002/pssc.201510259
       
  • ZnSe:Mn aqueous colloidal quantum dots for optical and biomedical
           applications
    • Authors: Thiago G. Silva; Igor M. R. Moura, Paulo E. Cabral Filho, Maria I. A. Pereira, Clayton A. Azevedo Filho, Goreti Pereira, Giovannia A. L. Pereira, Adriana Fontes, Beate S. Santos
      Abstract: In this study, we present the optimization of the optical properties of Mn2+ doped ZnSe QDs (also referred to as d‐dots) coated with thioglycolic acid in aqueous medium. The nanoparticles were characterized by ionic coupled plasma, electron paramagnetic resonance, transmission electron microscopy and X‐ray diffractometry. By applying a controlled dose of UV irradiation, we obtained efficient orange emitting d‐dots (4T1→ 6A1 transition centered at 580 nm). The results point out to a doping fraction in the nanoparticles smaller than 1% (0.89%), and that the Mn2+ ions are preferentially located close to the particle's surface. The UV photoactivation procedure has a definite influence on the emission intensity and on the colloidal stability of the particles. Photoactivated Mn2+ d‐dots were conjugated to Concanavalin A and labeled specifically Candida albicans yeast cells, by targeting carbohydrate residues depicting the successful use of these QDs as fluorescent probes. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-05-13T06:30:14.725451-05:
      DOI: 10.1002/pssc.201510300
       
  • The nature of boron‐oxygen lifetimedegrading centres in silicon
    • Authors: Vladimir Voronkov; Robert Falster
      Abstract: Light‐induced degradation of minority carrier lifetime in silicon is caused by the formation of two B‐O recombination centres: fast‐stage centres (FRC) and slow‐stage centres (SRC). FRC were concluded to emerge by a carrier‐assisted reconfiguration of a latent BO2 defect composed of a substitutional boron atom and an oxygen dimer. The nature of SRC however remained uncertain; this defect appeared to involve an interstitial boron atom rather than a substitutional one. More recent data on SRC in boron‐containing compensated p‐Si and n‐Si now show that the SRC actually emerge in the same way as FRC: by a reconfiguration of BO2, but from a different latent form. The two latent BO2 defects (the precursors for FRC and for SRC) are created during a cooling stage after the last high‐temperature anneal, and their concentration, proportional to the boron concentration and squared oxygen concentration, depends on the cooling rate. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-05-13T06:30:13.688865-05:
      DOI: 10.1002/pssc.201600016
       
  • Comparison between Si/SiO2 mid‐gap interface states and deep levels
           associated with silicon‐oxygen superlattices in p‐type silicon
           
    • Authors: Eddy Simoen; S. Jayachandran, A. Delabie, M. Caymax, M. Heyns
      Abstract: In this paper, the deep levels found by deep‐level transient spectroscopy in Si‐O superlattices on p‐type silicon substrates are compared with the band of near mid‐gap hole traps typically observed at the Si/SiO2 interface. In addition, the impact of a post‐deposition Forming Gas Annealing is investigated. A large similarity between the two material systems is reported, which indicates that similar silicon‐oxygen bonds may be responsible for the deep hole traps.(© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-05-13T06:30:12.682755-05:
      DOI: 10.1002/pssc.201600018
       
  • Towards multifunctional heterostructured materials: ZnO nanowires growth
           on mesoscale periodically patterned Si
    • Authors: Anisha Gokarna; Agnieszka Gwiazda, Hind Kadiri, Anna Rumyantseva, Komla Nomenyo, Roy Aad, Gilles Lerondel
      Abstract: We report the growth of ZnO nanowires on mesoscale periodically patterned silicon. The aim of this work is to go towards fabrication of multifunctional heterostructured materials for increasing the specific surface area and light absorption properties. ZnO nanowires (NWs) were grown by chemical bath deposition technique on patterned silicon. Silicon patterning was conducted by two methods, namely, laser interference lithography and nanosphere lithography. We have studied the structural and optical properties of the ZnO NWs grown on these silicon patterns. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-05-03T03:40:48.47202-05:0
      DOI: 10.1002/pssc.201510295
       
  • Structural, electronic and thermodynamic properties of SrxCa1‐xS: A
           first‐principles study
    • Authors: S. Labidi; M. Boudjendlia, M. Labidi, J. Zeroual, R. Bensalem, F. El Haj Hassan
      Abstract: The principal purpose of this work is to further the understanding of the structural, electronic, and thermodynamic properties of the SrxCa1–xS alloys (0≤x ≤1) in Rock‐salt phase using the full potential augmented plane wave (FP‐LAPW) method within density functional theory. The exchange‐correlation potential for structural properties was calculated by the standard local density approximation (LDA) and GGA (PBE) and the new form of GGA (WC) which is an improved form of the most popular Perdew‐Burke‐Ernzerhof (PBE), while for electronic properties, the alternative form of GGA modified by Becke‐Johnson exchange correlation potential (MBJ) was also applied. It is shown that investigation on the effect of composition on lattice constant, bulk modulus, and band gap for ternary alloys shows almost nonlinear dependence on the composition. On the other hand, the thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing ΔHm as well as the phase diagram. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-05-03T03:40:47.247638-05:
      DOI: 10.1002/pssc.201510247
       
  • Analysis of the Hall‐effect data on Mn‐doped GaAs with taking
           into account the Hall factor for nearest‐neighbor hopping conduction
           
    • Authors: Yasutomo Kajikawa
      Abstract: The experimental data of the temperature‐dependent Hall‐effect measurements on Mn‐doped p ‐GaAs reported by Wolos et al. [Phys. Status Solidi C 6, 2769 (2009)], which exhibit the characteristic of nearest‐neighbor hoping (NNH) conduction, have been analyzed. For NNH conduction, it is assumed that the conductivity is expressed as σib (T) ∝︁ T−3/2 exp(−T0/T) while the Hall factor is expressed as Aib (T) ∝︁ T exp(−T0H/T), where T0 and T0H are adjustable parameters. It is found that kBT0 increases from 9 to 21 meV in proportion to the cube root of the substitutional Mn acceptor concentration, being consistent with the theory for NNH conduction. It is also found that KNNH = T0H/T0 decreases from 1.45 to 1.15 with increasing the substitutional Mn acceptor concentration from 0.8×1017 to 4×1017 cm‐3, being different from the concentration‐independent value of KNNH = 2/3 or 1/6 predicted by the theories. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-05-02T06:10:06.853976-05:
      DOI: 10.1002/pssc.201600014
       
  • Effect of electron blocking layers on the conduction and valence band
           profiles of InGaN/GaN LEDs
    • Abstract: In this paper we investigate the effect of including an electron blocking layer between the quantum well active region and the p‐type layers of a light emitting diode has on the conduction and valence band profile of a light emitting diode. Two light emitting diode structures with nominally identical quantum well active regions one containing an electron blocking layer and one without were grown for the purposes of this investigation. The conduction and valence band profiles for both structures were then calculated using a commercially available Schrödinger‐Poisson calculator, and a modification to the electric field across the QWs observed. The results of these calculations were then compared to photoluminescence and photoluminescence time decay measurements. The modification in electric field across the quantum wells of the structures resulted in slower radiative recombination in the sample containing an electron blocking layers. The sample containing an electron blocking layer was also found to exhibit a lower internal quantum efficiency, which we attribute to the observed slower radiative recombination lifetime making radiative recombination less competitive. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-05-02T06:10:04.718911-05:
      DOI: 10.1002/pssc.201510288
       
  • High‐voltage photoconductive semiconductor switches fabricated on
           semi‐insulating HVPE GaN:Fe template
    • Authors: Yunfeng Chen; Hai Lu, Dunjun Chen, Fangfang Ren, Rong Zhang, Youdou Zheng
      Abstract: In this work, high‐voltage photoconductive semiconductor switches (PCSSs) with inter‐digitated contact electrodes are directly fabricated on semi‐insultating HVPE GaN:Fe template. The PCSS exhibits a cutoff wavelength of 365 nm and a dark resistivity of ∼1010 Ω cm. A maximum blocking voltage of more than 1100 V is obtained, corresponding to a breakdown electric field higher than 1.57 MV/cm for the GaN:Fe template. When excited by a 266 nm ultraviolet pulsed laser, the PCSS under 550 V bias could produce a peak photocurrent density of 387 A/cm2 within a rise time of ∼20 ns. The fall time of the photocurrent pulse is mainly RC time limited. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-04-14T04:12:19.711137-05:
      DOI: 10.1002/pssc.201510210
       
  • Properties of two‐dimensional electron gas in AlGaN/GaN HEMT
           structures determined by cavity‐enhanced THz optical Hall effect
    • Abstract: In this work we employ terahertz (THz) ellipsometry to determine two‐dimensional electron gas (2DEG) density, mobility and effective mass in AlGaN/GaN high electron mobility transistor structures grown on 4H‐SiC substrates. The effect of the GaN interface exposure to low‐flow‐rate trimethylaluminum (TMA) on the 2DEG properties is studied. The 2DEG effective mass and sheet density are determined tobe in the range of 0.30‐0.32m0 and 4.3‐5.5×1012 cm–2, respectively. The 2DEG effective mass parameters are found to be higher than the bulk effective mass of GaN, which is discussed in view of 2DEG confinement. It is shown that exposure to TMA flow improves the 2DEG mobility from 2000 cm2/Vs to values above 2200 cm2/Vs. A record mobility of 2332±61 cm2/Vs is determined for the sample with GaN interface exposed to TMA for 30 s. This improvement in mobility is suggested to be due to AlGaN/GaN interface sharpening causing the reduction of interface roughness scattering of electrons in the 2DEG. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-04-14T04:12:18.561768-05:
      DOI: 10.1002/pssc.201510214
       
  • Admittance of MIS structures based on graded‐gap MBE HgCdTe with
           Al2O3 insulator
    • Authors: Alexander V. Voitsekhovskii; Sergey N. Nesmelov, Stanislav M. Dzyadukh, Vladimir V. Vasil`ev, Vasiliy S. Varavin, Sergey A. Dvoretsky, Nikolay N. Mikhailov, Maxim V. Yakushev, Georgiy Y. Sidorov
      Abstract: The paper presents the results of studies of the admittance of MIS structures based on heteroepitaxial MBE n (p)‐Hg0.78Cd0.22Te with insulator coating SiO2/Si3N4 and Al2O3 in the test signal frequency range 10 kHz‐1 MHz at temperatures ranging from 8 to 220 K. The main parameters of MIS structures with different insulators were determined. MIS structures with Al2O3 have a large enough insulator capacitance (compared to SiO2/Si3N4), a significant modulation capacitance on the CV characteristics, high dielectric strength and low values of the flat‐band voltage. The effective charge density found from the value of the flat‐band voltage and slow interface trap density for structures with Al2O3 comparable with the corresponding densities for structures with SiO2/Si3N4. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-04-14T04:12:17.329356-05:
      DOI: 10.1002/pssc.201510227
       
  • Electrical and optical studies of a tellurium‐related defect in
           molecular‐beam epitaxy‐grown HgCdTe
    • Abstract: Electrical and optical studies of defects in molecular beam epitaxy (MBE)‐grown HgCdTe films, undoped and doped with arsenic, were carried out. By comparing results of ion milling‐assisted Hall‐effect measurements with micro‐Raman spectroscopy data, it was shown that the films contained electrically neutral defects related to excessive tellurium. It is suggested that these defects are Te nanocomplexes and that they are typical of the MBE HgCdTe technology. Under ion milling, they get electrically activated by interstitial mercury and form donor centers with concentration of ∼1017 cm‐3, which allows for detecting them with measurements of electrical parameters of the material. Also, it can be suggested that in films doped with arsenic with high‐temperature cracking, As2 dimers in the arsenic flux react with excessive tellurium and form As2Te3 donor complexes, thus preventing formation of Te nanocomplexes. Arsenic activation annealing may break As2Te3 complexes and release Te, which can again form the complexes under ion milling. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-04-14T04:12:16.310419-05:
      DOI: 10.1002/pssc.201510234
       
  • Photosensitive MIS structures with ultrathin dielectric based on
           CdXHg1‐XTe (x ∼ 0.4)
    • Authors: Valeriy G. Kesler; Alexander A. Guzev, Sergey A. Dvoretskiy, Evgeniy R. Zakirov, Anatoliy P. Kovchavtsev, Zoya V. Panova, Maxim V. Yakushev
      Abstract: The work is aimed to studying a possibility of CdHgTe surface passivation and stabilization by tunnel‐thin (∼ 2 nm) native oxide formed by glow discharge plasma oxidation. Kinetics of MCT plasma treatment in two regimes has been obtained. Investigation of the stabilization effect during vacuum annealing and platinum deposition has been performed. It has been established that presence of a native oxide layer on MCT surface results in elimination of mercury out diffusion during the processes. MIS structures with platinum contacts and thin native oxide have been made. They have rectifying behaviour in contrast with structures without the native oxide layer. The barrier height and the detectivity have been determined from the capacitance‐voltage and current‐voltage dependences. The detectivity value of 4×1011cm.Hz1/2W‐1 (at 78 K) determined by dark current shot noise has been reached. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-04-14T04:12:15.186306-05:
      DOI: 10.1002/pssc.201510275
       
  • Growth of zinc sulfide by mist chemical vapor deposition depending on mist
           size and thermal conditions in susceptor
    • Authors: Kazuyuki Uno; Yuichiro Yamasaki, Ping Gu, Ichiro Tanaka
      Abstract: Zinc sulfide (ZnS) films were successfully grown by using mist chemical vapor deposition (mist‐CVD) with fine‐channel susceptor made of quartz. For the investigation of growth dynamics, two types of mist generators and two types of susceptors were prepared and distribu¬tion profiles of film thickness were examined. Thermal efficiency of susceptor depends on heat¬penetration efficiency and line‐velocity of the mists, which are influenced by the fine‐channel gap‐height of the susceptors. Using larger size of mists requires higher thermal efficiency in susceptor to obtain a flat thickness distribution. This result indicates that the optimization of the mist size and the susceptor structure is important for the film uniformity of grown films by the mist‐CVD. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-04-14T04:12:13.791215-05:
      DOI: 10.1002/pssc.201510309
       
  • Fabrication and characterization of two‐dimensional cubic AlN
           photonic crystal membranes containing zincblende GaN quantum dots
    • Abstract: We successfully developed a process to fabricate freestanding cubic aluminium nitride (c‐AlN) membranes containing cubic gallium nitride (c‐GaN) quantum dots (QDs). The samples were grown by plasma assisted molecular beam epitaxy (MBE). To realize the photonic crystal (PhC) membrane we have chosen a triangular array of holes. The array was fabricated by electron beam lithography and several steps of reactive ion etching (RIE) with the help of a hard mask and an undercut of the active layer. The r/a‐ ratio of 0.35 was deter‐ mined by numerical simulations to obtain a preferably wide photonic band gap. Micro‐photoluminescence (µ‐PL) measurements of the photonic crystals, in particular of a H1 and a L3 cavity, and the emission of the QD ensemble were performed to characterize the samples. The PhCs show high quality factors of 4400 for the H1 cavity and about 5000/3000 for two different modes of the L3 cavity, respectively. The energy of the fundamental modes is in good agreement to the numerical simulations. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-04-14T04:12:12.88812-05:0
      DOI: 10.1002/pssc.201600010
       
  • Fabrication of GaN quantum dots using Ga droplet epitaxy and thermal
           annealing by metal organic chemical vapor deposition
    • Authors: Zhiqiang Qi; Yanyan Fang, Changqing Chen, Jiangnan Dai
      Abstract: Optically active GaN quantum dots are grown by droplet heteroepitaxy and post‐growth annealing. The evolution of morphology and optical properties of thermal annealing GaN QDs have been investigated. The results show that thermal annealing under NH3/N2 ambience is a necessary condition for maintaining the optimal QDs morphology and improving optical properties of GaN QDs. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-04-14T03:42:16.08676-05:0
      DOI: 10.1002/pssc.201510154
       
  • Fabrication and characterization of Au/Zn composite electrode on
           p‐CdZnTe (111) B plane
    • Abstract: Electrode fabrication is a key procedure for preparation of high‐performance CdZnTe detectors, and the metal–semiconductor contact contributes greatly to the performance of detectors. In the present paper, a vacuum evaporation method was used to deposit a Au/Zn composite electrode on the (111) plane of p‐CdZnTe. Based on the AFM, SEM, current–voltage testing and the barrier‐height calculations, the effects of an Au/Zn contact on CdZnTe detector properties were investigated. The results showed that a lower Schottky barrier height was attained by depositing a Au layer on p‐CdZnTe(111) A plane and a Au/Zn double layers on (111) B plane, decreasing the influence of the Te‐enriched surface on the metal–semiconductor contact, and suggesting a better ohmic contact for CdZnTe detectors. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-29T03:34:04.771146-05:
      DOI: 10.1002/pssc.201510279
       
  • Exciton recombination in spontaneously formed and artificial quantum wells
           AlxGa1‐xN/AlyGa1‐yN (x
    • Authors: A. A. Toropov; E. A. Shevchenko, T. V. Shubina, V. N. Jmerik, D. V. Nechaev, G. Pozina, P. Bergman, B. Monemar, S. Rouvimov, S. V. Ivanov
      Abstract: We report on photoluminescence (PL) spectroscopy and electron microscopy studies of an AlGaN quantum well (QW) structure grown by molecular beam epitaxy under metal‐rich conditions with substrate rotation. Both techniques reveal unintentional formation within the AlGaN barriers of a quasiperiodic structure of thin Ga‐rich layers, whose period is controlled by both the substrate rotation rate and the AlGaN growth rate. These compositional modulations act as 1‐3 monolayer thick QWs emitting below 250 nm with an internal quantum efficiency (IQE) as high as ∼30% at room temperature under weak excitation. Variational calculations of the QW exciton properties indicate that the observed high IQE can result from strong three‐dimensional localization of the excitons confined in the narrow QWs. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-29T03:34:03.912289-05:
      DOI: 10.1002/pssc.201600009
       
  • Effect of superlattice on light output power of InGaN‐based
           light‐emitting diodes fabricated on underlying GaN substrates with
           different dislocation densities
    • Authors: Kohei Sugimoto; Yusho Denpo, Narihito Okada, Kazuyuki Tadatomo
      Abstract: We evaluated the electrical properties of InGaN‐based light‐emitting diodes (LEDs) with a surperlattice (SL) layer just below the MQWs for forming V‐shaped pits (V‐pits) on underlying GaN substrates with different dislocation densities (DDs). The SL was effective for improving the EL intensity for all the LEDs with different DDs. However, the improvement ratio decreased with decreasing DD. The SL is effective for performance improvement of the LEDs with high DDs. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-29T03:24:31.796145-05:
      DOI: 10.1002/pssc.201510203
       
  • Analysis of breakdown characteristics in source field‐plate
           AlGaN/GaN HEMTs
    • Authors: Hiraku Onodera; Hideyuki Hanawa, Kazushige Horio
      Abstract: Two‐dimensional analysis of off‐state breakdown characteristics of source field‐plate AlGaN/GaN HEMTs is performed by considering a deep donor and a deep acceptor in a buffer layer. It is shown that the introduction of field plate is effective in improving the breakdown voltage, but it can decrease with the field‐plate length, and hence its optimum length should exist. It is also shown that the breakdown voltage of the source field‐plate structure is a little lower than that of the gate field‐plate structure when the field‐plate length is short, because the electric field at the drain edge of the gate becomes higher. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-29T03:24:30.239737-05:
      DOI: 10.1002/pssc.201510155
       
  • Power density dependent photoluminescence spectroscopy and Raman mapping
           of semi‐polar and polar InGaN/GaN multiple quantum well samples
    • Abstract: We present a study of polar and semi‐polar InGaN/GaN multiple quantum well (MQW) samples. Power density dependent photoluminescence (PL) was conducted on the samples. The polar sample exhibited a large blue shift of 65 nm in the peak PL from low to high power density compared to 10 nm for the semi polar sample. The semi‐polar sample displayed “chevron” shaped surface features. These chevrons were mapped using micro‐PL spectroscopy and showed a red shift of 10 nm at the “join” of the chevron. Raman mapping of the chevron also showed an increase in amplitude of the Raman shift in this area. Angle dependent polarised Raman measurements were conducted on the semi‐polar sample to potentially isolate the scattering from the InGaN layers. However, polarised mapping exhibited similar behaviour to the unpolarised maps at the chevron join, indicating that the GaN bulk layer is responsible for the observed scattering. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-29T03:24:27.423218-05:
      DOI: 10.1002/pssc.201510196
       
  • Comparative performance assessment of SiC and GaN power rectifier
           technologies
    • Authors: Sauvik Chowdhury; T. Paul Chow
      Abstract: Silicon carbide and gallium nitride based Schottky and pin junction power rectifiers offer different performance trade‐offs in terms of metrics such as forward voltage drop, switching energy loss and surge current capability. The goal of this paper is to identify the application space for different rectifier technologies. An analytical comparison between the performance of different power rectifier diodes for breakdown voltages ranging from 600V to over 8 kV is presented. It is shown that although GaN SBD offers some advantage over SiC diodes due to lower losses, low surge current capability of GaN may hinder its widespread adoption in applications. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-29T03:24:25.856495-05:
      DOI: 10.1002/pssc.201510204
       
  • High accuracy equivalent circuit model for GaN GIT bi‐directional
           switch
    • Abstract: The simple and high‐accuracy equivalent circuit model for GaN‐GIT bi‐directional switch have been constructed by eliminating the gate resistance dependence from the capacitance parameters and employing the parallel gate resistance circuit with the diode. By the new methods, the calculated waveforms, switching losses and switching times agree well with the experimental ones, and the accuracy between the calculations and the experiments are more than 90%. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-29T03:24:21.482969-05:
      DOI: 10.1002/pssc.201510205
       
  • 3.2 mΩcm2 enhancement‐mode GaN MOSFETs with breakdown voltage
           of 800 V
    • Authors: Hisashi Saito; Miki Yumoto, Shigeto Fukatsu, Yosuke Kajiwara, Aya Shindome, Kohei Oasa, Yoshiharu Takada, Kunio Tsuda, Masahiko Kuraguchi
      Abstract: Enhancement‐mode GaN metal‐oxide‐semiconductor field‐effect transistors (MOSFETs) have been reported. We utilized the atomic layer deposition (ALD) method for the fabrication process of the gate dielectric, in order to suppress plasma damage and obtain high‐quality dielectric film. In the fabricated devices, the specific on‐state resistance of 3.2 mΩcm2 and the breakdown voltage of 800 V were achieved. Moreover, a 10‐year lifetime with a cumulative failure rate of 0.1% was guaranteed at over 20 V. This voltage was twice the operation voltage of 10 V. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-29T03:24:14.423488-05:
      DOI: 10.1002/pssc.201510225
       
  • Electronic spectrum of Bi‐related defects in crystalline CdTe
    • Authors: Vladimir Krivobok; Sergey Nikolaev, Evgeny Onischenko, Anna Pruchkina, Sergey Kolosov, Yuri Klevkov, Victor Bagaev
      Abstract: Using measurements of conductivity and low‐temperature photoluminescence, we have studied electronic levels in the band gap of CdTe:Bi and CdTe:Bi,Cl single crystals grown by the modified Bridgman technique. Three type of deep levels (EV+0.29 eV, EV+0.4 eV, EV+0.72 eV) and Bi‐related shallow acceptor have been observed depending on the doping conditions. Energy spectrum of a shallow Bi‐related acceptor has been measured and its low symmetry has been established. The tentative interpretation for all the levels observed has been proposed. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:20:15.499157-05:
      DOI: 10.1002/pssc.201510274
       
  • Growth and characterization of Mg1‐xCdxO thin films
    • Abstract: In this paper, we study the growth of thin films of the Mg1–xCdxO alloy in the Mg‐rich range of compositions by using the metal organic chemical vapour deposition (MOCVD) method at low pressure. X‐ray diffraction (XRD) has been used to analyse the compound formation and the progressive incorporation of Cd2+ ions into the cubic MgO lattice. Both, layers with a single‐cubic phase of Mg1–xCdxO and layers with a phase separation, where Cd1–xMgxO and Mg1–xCdxO coexist, have been studied. Finally, a morphological study of the layers has been carried out by using scanning electron microscopy (SEM) and the layers' composition has been measured by energy dispersive X‐ray analysis (EDX). (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:20:14.563297-05:
      DOI: 10.1002/pssc.201510276
       
  • Structural, optical and magnetic characteristics of II‐VI
           semiconductor nanocrystal‐graphene hybrid nanostructures
    • Authors: Andriy I. Savchuk; Ihor D. Stolyarchuk, Serhii A. Savchuk, Eugeniusz M. Sheregij, Jacek Polit
      Abstract: CdS, CdTe, ZnO, and ZnO:Co nanocrystals and related hybrid nanostructures, in which the nanoparticles combined with graphene, have been studied. Different chemical approaches for synthesis of II‐VI semiconductor nanocrystal‐graphene hybrids have been applied depending on chemical composition. Transmission electron microscopy characterizations proved the formation of graphene based hybrid nanostructures. Absorption spectra near band‐gap edge have shown changes due to the interaction of the nanocrystals with graphene. The revealed photoluminescence quenching effect in II‐VI semiconductor nanocrystal‐graphene hybrids can be served as evidence for electron transfer from the nanoparticles to graphene. Results of Faraday rotation measurements in doped ZnO:Co nanocrystals and their hybrids at room temperature demonstrated paramagnetic behaviour for both kinds of samples. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:20:13.065783-05:
      DOI: 10.1002/pssc.201510283
       
  • Structural properties and vertical transport in ZnSe/CdSe superlattices
           grown on an In0.3Ga0.7As metamorphic buffer layer
    • Authors: E. A. Evropeytsev; S. V. Sorokin, G. V. Klimko, S. V. Gronin, I. V. Sedova, K. G. Belyaev, S. V. Ivanov, G. Pozina, A. A. Toropov
      Abstract: We report on the growth by molecular‐beam epitaxy of short‐period ZnSe/CdSe superlattices (SLs) on an In0.3Ga0.7As metamorphic buffer layer. Such SLs are considered as a promising material for a wide band‐gap photoactive p‐n junction in a hybrid monolithic Ge/InxGa1‐xAs/Iny(Al,Ga)1‐yAs/II‐VI solar cell. Lattice‐matching of the SLs to the In0.3Ga0.7As layer is confirmed by X‐ray diffractometry. Vertical transport of photoexcited carriers is investigated by means of both steady state and time‐resolved photoluminescence techniques in heterostructures containing the ZnSe/CdSe SL with an enlarged quantum well (EQW). Characteristic times of the carrier transport across the SL towards EQW are evaluated in the temperature range 120–300 K. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:20:11.814723-05:
      DOI: 10.1002/pssc.201510305
       
  • Influence of source transport rate upon fractions of Mg and Se in
           Zn1‐xMgxSeyTe1–y layers grown by metalorganic vapor phase
           epitaxy
    • Authors: Katsuhiko Saito; Masakatsu Abiru, Eiichiro Mori, Yasuhiro Araki, Daichi Tanaka, Tooru Tanaka, Qixin Guo, Mitsuhiro Nishio
      Abstract: The growth of undoped Zn1–xMgx Sey Te1–y layers on (100) ZnTe substrates by metalorganic vapor phase epitaxy has been carried out. The fractions of Mg and Se, Raman property and surface roughness have been characterized as a function of bis‐methylcyclopentadienyl‐magnesium ((MeCp)2Mg) or diethylselenide (DESe) transport rates. It has been demonstrated that the Mg and Se fractions in Zn1–xMgx Sey Te1–y layer can be controlled successfully by these source transport rates. Furthermore, the behaviors of two Raman peaks related to ZnSeTe‐like longitudinal optical phonon mode and MgSeTe‐like one have been clarified for some Mg and Se fractions in Zn1–xMgx Sey Te1–y layers. It has been shown by varying (MeCp)2Mg or DESe transport rates that Zn1‐xMgx Sey Te1–y layer nearly‐lattice‐matched to ZnTe substrate shows low surface roughness. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:20:10.744695-05:
      DOI: 10.1002/pssc.201510304
       
  • A comparative study of the gas sensing properties of hierarchical ZnO
           nanostructures
    • Abstract: Two types of ZnO nanostructure have been fabricated to make a comparative study on their gas sensing performance: the conventional ZnO nanowire arrays were synthesized by hydrothermal method and the hierarchical ZnO nanowires/nanofibers nanostructures were prepared through a combination of the hydrothermal and electrospinning methods. Field emission scanning electron microscopy study showed a quiet homogeneous morphology both for both nanostructures. Three kinds of commonly used gases, such as ethanol, acetone and ammonia were chosen for ZnO nanostructure gas sensing property study. The UV‐Visible spectroscopy measurements showed a higher detection sensitivity of ZnO NWs for ammonia compared to ethanol and acetone, and an enhanced sensing performance for the hierarchical nano‐ structure, which has a higher surface to volume ratio. On the other hand, the enhancement was more obviously in the case of ethanol sensing. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:20:09.844942-05:
      DOI: 10.1002/pssc.201510301
       
  • 2D‐localization and delocalization effects in quantum Hall regime in
           HgTe wide quantum wells
    • Authors: Svetlana V. Gudina; Yurii G. Arapov, Vladimir N. Neverov, Sergey M. Podgornykh, Mikhail R. Popov, Nina G. Shelushinina, Mikhail V. Yakunin, Sergey A. Dvoretsky, Nikolay N. Mikhailov
      Abstract: We have measured the longitudinal and Hall resistivities in the quantum Hall regime at magnetic fields B up to 9 T and temperatures T = (2.9–50) K for HgTe/HgCdTe heterostructure with wide HgTe quantum well. The results are analysed within the scaling concept for the conductivity on the delocalized states at the center of the Landau level and within the variable‐range hopping model for the conductivity on the localized states between the Landau levels. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:20:08.88983-05:0
      DOI: 10.1002/pssc.201510299
       
  • Tamm plasmon polaritons in the visible spectral region and its optical
           properties in ZnSe‐based microcavities
    • Abstract: We report on the formation of Tamm plasmon (TP) modes in the visible spectral region at the interface between a Ag film and a ZnSe‐based distributed Bragg reflector (DBR). The tuning of the TP eigenenergies within the stop‐band in dependence on the DBR top layer thickness is investigated by micro‐reflectivity measurements. The experimental findings are compared with calculations using the transfer matrix method. The latter calculations show that strong coupling can be achieved between quantum well (QW) excitons and the TP modes. In addition, the Rabi‐splitting energy can be enhanced in a simple TP structure by increasing the number of QWs inside the top layer of the DBR. When a metal layer is deposited on a cold MC sample, micro‐reflectivity spectra show a blue shift of the cavity resonance. The TP modes are likewise observed in the same MC sample when reducing the top layer thickness of the DBR. This shift of cavity resonance and formation of TP mode are in good agreement with calculations. These results are rather promising in order to realize a spatial confinement of the polaritons by utilizing metal strips. Such channeling of polaritons opens the way to practical demonstration of exciton‐polariton integrated circuits. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:20:08.001662-05:
      DOI: 10.1002/pssc.201510296
       
  • Effect of Al doping in the Ag layer of MgZnO/Ag/MgZnO
           
    • Authors: Yukiko Sugimoto; Kanae Igarashi, Shinya Shirasaki, Akihiko Kikuchi
      Abstract: Transparent conductive films (TCFs) with dielectric/metal/dielectric (DMD) structure covering the UVA (λ = 315–380 nm) and visible wavelength region (380–780 nm) were fabricated using Al‐doped Mg0.4Zn0.6O (AMZO) dielectric and 1.7 at% Al‐doped Ag (Ag(Al)) metal layers. The AMZO/Ag(Al)/AMZO‐DMD film with a 7 nm thick Ag(Al) layer after annealing in vacuum at 400 °C showed superior performance as a TCF, i.e., average transmittance from UVA to visible region (315–780 nm) of 88.2% and sheet resistance of 7.6 Ω/sq. The effect of Al doping on optical transmission, sheet resistance, surface morphology, and thermal durability of the AMZO/Ag(Al)/AMZO‐DMD films were also investigated. The 1.7 at% Al doping suppressed the initial island growth of the thin Ag layer and the plasmon resonance absorption dipped in the optical transmission spectra. Al doping in the Ag layer also improved the thermal durability of AMZO/Ag/AMZO‐DMD films. The threshold temperature for Ag void formation caused by metal segregation increased from 300 °C (DMD with a pure Ag layer) to 400 °C (DMD with an Al‐doped Ag layer). (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:20:07.072077-05:
      DOI: 10.1002/pssc.201510290
       
  • Influence of the number of electronically coupled CdSe/ZnSe QD planes on
           characteristics of optically pumped green lasers
    • Authors: I. V. Sedova; E. V. Lutsenko, S. V. Sorokin, A. G. Vainilovich, S. V. Gronin, G. P. Yablonskii, M. Aljoheni, A. Aljerwi, A. Alyamani, S. V. Ivanov
      Abstract: Structural properties and laser characteristics of true green (λ=530‐550 nm) ZnSe‐based optically pumped laser heterostructures with several (up to three) CdSe/ZnSe quantum dot (QD) planes in the active region were studied in details. Optimization of the MBE growth conditions to reduce the non‐equilibrium defect density in the active region as well as the active region design allowed obtaining nearly the same rather low laser threshold values of Ithr∼4 kW/cm2 at Lcav∼100 μm for all the samples. The internal laser parameters were determined by measuring the laser threshold and differential quantum efficiency as functions of the cavity length. The design of laser structures provides high excitation homogeneity of the active region due to strong enough carrier tunneling between QD layers spaced by 5‐nm‐thick ZnSe barriers, which is confirmed by the sub‐linear dependence of the transparency excitation intensity versus number of QD planes in the active region (IT = 0.556, 1.037, and 1.311 kW/cm2). The triple‐QD‐plane laser structure demonstrates significant increase in characteristic gain up to ΓG0=161.62 cm‐1. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:20:05.605287-05:
      DOI: 10.1002/pssc.201510289
       
  • Numerical modeling and simulation of ZnO nanowire devices for energy
           harvesting
    • Abstract: Duo to their multifunctional properties, the piezoelectric ZnO nanowires are of great interest in many applications such as the energy harvesting. In this work, a numerical modelling based on the finite element method was performed to study the potential distribution inside the ZnO nanowire and the impact of the geometric parameters on the generated piezopotential both in bending and compression deformation. In this context, a nanowire discharge behavioural study was carried out in order to obtain an analytic expression which connects the piezopotential and nanowire geometrical parameters in the bending deformation. Furthermore, a heuristic algorithm Particle Swarm Optimization (PSO) has been used in order to improve the electromechanical performance of ZnO nanowire based nanogenerator. It is fount that under the same order of force applied on a nanowire, the compression mode results in a piezopotential 9 times larger than that in the bending deformation. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:10:17.801655-05:
      DOI: 10.1002/pssc.201510270
       
  • Electron–phonon interaction in II‐VI quantum wells
    • Authors: A. Yu. Maslov; O. V. Proshina
      Abstract: The theory of charge‐particle interaction with polar optical phonons is developed for II‐VI compounds‐based heterostructures in which the symmetries of the quantum well and barrier materials are different. The parameters of the electron–phonon interaction are found for the structures in which the material of hexagonal symmetry is used for creating a quantum well or barriers. It is shown that the electron–phonon interaction depends on the anisotropy of the dielectric parameters of the hexagonal material for both cases. Compared to previously obtained results for a quantum well based on the material of cubic symmetry both enhancing and weakening of polaron effects are possible. The obtained results are applied to the explanation of polaron mass magnitude in the quantum well based on ZnO‐ZnMgO. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:10:16.973941-05:
      DOI: 10.1002/pssc.201510263
       
  • Investigation of yellow/green II‐VI compound semiconductor laser
           diode structures on InP substrates
    • Authors: Ryohei Kobayashi; Shingo Takamatsu, Koji Fukushima, Katsumi Kishino, Ichirou Nomura
      Abstract: II‐VI‐compound‐semiconductor laser diode (LD) structures on InP substrates were investigated using device simulations and waveguide analysis. Our simulations showed that electron injection from the n‐cladding into the active layer is hindered by the n‐side barrier layer between the n‐cladding and active layer. Consequently, holes are not injected into the active layer but instead leak to the n‐side layers. It was shown that carrier injection efficiency can be improved by removing the n‐barrier. On the contrary, no large differences were observed between the optical confinement factors of the LD structures with and without the n‐barrier layer. In experiments, we have fabricated the LD structures with and without the n‐barrier layer on InP substrates using molecular beam epitaxy. The turn‐on voltage of the device without the n‐barrier was smaller than that for the device with the n‐barrier by about 5 V. Spontaneous orange emissions around 603 nm were observed for the devices without the n‐barrier. In contrast, no emission was observed for the devices with the n‐barrier. These results prove that the carrier injection into the active layer is enhanced by the removal of the n‐barrier, leading to improved the device performances. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:10:16.108611-05:
      DOI: 10.1002/pssc.201510255
       
  • Effects of strontium concentration on structural, electronic, optical and
           thermodynamic properties of Pb1‐xSrxS
    • Authors: Jazia Zeroual; Salima Labidi, Malika Labidi, Rachid Bensalem
      Abstract: Theoretical investigations of structural, electronic, optical and thermodynamic properties of Pb1‐xSrxS with rocksalt crystal structure are reported, theoretical calculations are mainly based on the full potential linearized augmented plane wave (FP‐LAPW) method within the density functional theory (DFT) the generalized gradient approximation (GGA) of Perdew et al. The dependence of the lattice parameters, band gaps, dielectric constants, refractive indices, and mixing entropies on the composition x were analyzed mainly for x = 0, 0.25, 0.50, 0.75 and 1. The lattice constant for Pb1‐xSrxS exhibits a marginal deviation from the Vegard’s law. A significant deviation of the bulk modulus from linear concentration dependence was observed for the alloy. The microscopic origins of the gap bowing were detailed and explained. The composition dependence of the dielectric constant and refractive index was studied using different models. Besides, a regular‐solution model is used to investigate the thermodynamic stability of the alloys, which mainly indicates a phase miscibility gap. In fact and since there is a good agreement between our main results and the available experimental data for the binary compounds which may be a support for the results of the ternary alloys reported here for the first time. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:10:14.867908-05:
      DOI: 10.1002/pssc.201510237
       
  • The efficiency droop impact of GaN‐based LEDs on the performance of
           OFDM visible light communication system
    • Authors: Huimin Lu; Tongjun Yu, Chuanyu Jia, Yini Zhang, Jianping Wang, Guoyi Zhang
      Abstract: The physical mechanism in efficiency droop of GaN‐based LEDs fabricated by metal organic chemical vapor deposition (MOCVD) was investigated by experiment and calculation. On this basis, the efficiency droop impact on the performance of orthogonal frequency division multiplexing (OFDM) visible‐light communication (VLC) system was analyzed. The numerical results show that the VLC system performance decreases obviously under the impact of the LED efficiency droop. And, the performance deterioration of OFDM VLC system aggravates as FFT sampling rate increase due to signal dynamic range enlargement. Furthermore, the efficiency droop impact on the VLC performance can be alleviated by adjusting the LED operating condition. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-16T06:10:10.818985-05:
      DOI: 10.1002/pssc.201600002
       
  • Comparative studies of CdSe/ZnSe quantum dot structures epitaxially grown
           with or without a sub‐monolayer CdTe stressor
    • Authors: M. V. Rakhlin; K. G. Belyaev, I. V. Sedova, S. V. Sorokin, S. V. Gronin, A. A. Usikova, A. A. Sitnikova, P. N. Brunkov, S. V. Ivanov, A. A. Toropov
      Abstract: We report on comparative studies of the emission properties of CdSe/ZnSe quantum dots (QDs) grown by molecular beam epitaxy either with or without predeposition of a sub‐monolayer CdTe stressor, and in the latter case, either with or without in‐situ thermal annealing. The emission of a limited number of QDs was registered in all samples by micro‐photoluminescence confocal spectroscopy through 500‐nm‐size round apertures opened in a non‐transparent gold mask by ball assisted etching technique. The measurements reveal the lowest density of emitting QDs in the sample grown with the in‐situ annealing that is attributed to both ripening of the CdSe QDs and strain relaxation in the largest QDs, followed by formation of defects serving as centres of nonradiative recombination. The employment of the CdTe stressor causes narrowing of the total QDs emission band and simultaneous broadening of the single‐QD lines that is consistent with the formation of a relatively homogeneous dense array of type‐I CdSe/ZnSe QDs adjoining type‐II Zn(Cd)Te/ZnSe nanostructures. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-03T09:15:19.330217-05:
      DOI: 10.1002/pssc.201510302
       
  • Growth, structural and optical properties of ZnO/ZnMgO core‐shell
           heterostructures
    • Authors: S. A. Said Hassani; C. Sartel, C. Vilar, G. Amiri, A. Lusson, V. Sallet, P. Galtier
      Abstract: ZnO nanowires have been grown by metalorganic chemical vapor deposition on sapphire substrates. The use of N2O and DEZn as oxygen and zinc precursors combined with high temperature leads to the spontaneous growth of vertical ZnO nanowires (NWs) on underlying three dimensional islands present at the bottom of each nanowire. These nanowires are grown along the c axis of the wurtzite structure, exhibit well defined m‐plane facets and are free of extended defects. This configuration is favorable to band‐gap engineering studies. Based on this, we have grown a series of radial ZnO/ZnMgO shells and quantum wells with different thicknesses and Mg concentrations. ZnxMg1‐xO alloys have been grown using O2, (MCp)2Mg and DEZn as oxygen, magnesium and zinc precursors. Low temperature photoluminescence spectroscopy and transmission electron microscopy have assessed Mg concentrations in the shell up to 20 %. Electron diffraction reveals that the ZnMgO alloyed structure is, at least partially, ordered. Micro‐photoluminescence performed on a single ZnO/ZnMgO coreshell nanowire including a quantum well exhibits luminescence properties, with a lateral quantum confined emission. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-03T09:15:16.824029-05:
      DOI: 10.1002/pssc.201600001
       
  • Electric field inhomogeneity in ohmic‐type CdTe detectors measured
           by time‐of‐flight technique
    • Authors: Kazuhiko Suzuki; Takayuki Sawada, Satoru Seto
      Abstract: The bias‐induced instability of the internal electric field in Ohmic‐type CdTe gamma‐ray detectors is investigated by using the time‐of‐flight technique. Based on the solution of one dimensional Poisson equation, transient current waveforms at different delays of laser excitation from the bias application and at different temperatures are analysed It is shown that under DC bias application, the internal electric field decreases with depth because of the positive space charge buildup in the detectors. Further, the origin of the space charge is attributed to the injection and successive trapping of holes from the anode side at the early stage of evolution and then later to the thermal release of electrons from a deep donor at 0.64 eV. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-03T09:15:14.993931-05:
      DOI: 10.1002/pssc.201510239
       
  • Manifestation of strong d‐p hybridization in photoluminescence
           spectra of ZnO:Ni and ZnO:Co
    • Authors: V. I. Sokolov; N. B. Gruzdev, V. A. Pustovarov, V. N. Churmanov
      Abstract: For the first time photoluminescence and photoluminescence excitation spectra for ZnO:Co and ZnO:Ni crystals were obtained at the excitation by the synchrotron radiation in the interval of energy of (3.7‐21) eV, T = 8 K. It is shown that these spectra are formed by intense radiative transitions through 3d charge transfer states in the band gap. This fact evidences about much stronger hybridization between d‐states of impurity and p‐states of anions in comparison with other II‐VI:3d compounds. It is very important for applications in optoelectronics, for visualization of ultraviolet radiation and understanding of photocatalytic activity of ZnO:3d nanocrystals in the visible region of the spectrum. From the comparison of PLE spectra for ZnO:Co and ZnO:Ni with the spectrum of calculated DOS for ZnO it is revealed a visible transformation of part of valence band states due to a strong d‐p hybridization. Obtained results allow us to consider ZnO:3d as a compounds with a strong correlations. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-03T09:15:08.729506-05:
      DOI: 10.1002/pssc.201510241
       
  • Dislocations in MCT heteroepitaxial structures on (013) substrates and
           possibilities of dislocation density reducing
    • Authors: Yury Sidorov; Ivan Loshkarev, Irina Sabinina, Evgeny Trukhanov, Vasily Varavin, Maksim Yakushev, Aleksei Kolesnikov
      Abstract: Dislocations in heterostructures CdTe/ZnTe/GaAs(013) and CdTe/ZnTe/Si(013) were investigated using selective etching and transmission electron microscopy. The calculations of critical film thickness hc were fulfilled for 12 various slip systems, the experimental results were obtained for 4 of them. Misfit dislocations are introduced in a ZnTe film at the stage of formation of the first monolayers. With their introduction, the crystal lattices of the substrate and the film unfold relative each other that is confirmed by X‐ray diffraction measurements. An increase in the dislocation density into the CdTe and HgCdTe films was observed using layer‐by‐layer etching. That is testifies to the annihilation of threading dislocations during the growth of CdTe and MCT films. The dislocation annihilation rate is higher in films grown on GaAs(013) than on Si(013). Perhaps this is due to the higher proportion of gliding dislocations in CdTe films on GaAs substrates (013). It was made annealing of MCT films under cyclic temperature change in such way that activity of MCT components was changed to enhance the non‐conservative motion of dislocations. As a result, the density of penetrating dislocations in the active areas in MCT films on silicon substrates was decreased to the value of 2.5×106 cm‐2. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-03T09:15:05.639755-05:
      DOI: 10.1002/pssc.201510243
       
  • Development of ZnSe‐based organic–inorganic hybrid
           UV‐APDs array
    • Authors: Tomoki Abe; Ryoichi Inoue, Takeru Fujimoto, Kenta Tanaka, Shigeto Uchida, Hirofumi Kasada, Koshi Ando, Kunio Ichino
      Abstract: Recently, we have developed organic (PEDOT:PSS)–inorganic (ZnSSe) hybrid avalanche photodiode (APD) with long life time and its array. In this article, we review the development of the organic–inorganic hybrid‐type ZnSe‐based UV‐APDs array. We used PEDOT:PSS as UV transparent hole‐transport conducting polymer window layers formed by inkjet printing technique. We have successfully fabricated low dark current ultraviolet hybrid APDs. The hybrid APD device has exhibited very low voltage APD operation at 29 V and extremely low dark current of 10‐11 A/mm2 in the avalanche breakdownregion. The hybrid APD also has shown maximum multiplication factor of 45 and high sensitivity ∼ 3 A/W at the ultraviolet region (∼ 300 nm). A stable device operation is established using polyimide passivation and sealed package with N2 atmosphere. We also demonstrated integrated devices operation in APD mode with very small photosignal cross‐talk of ‐50 dB. The tail of current‐profile was determined as 8 μm by using in‐plane electron‐beam induced current (EBIC) measurement. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-03T09:15:02.679457-05:
      DOI: 10.1002/pssc.201510273
       
  • The local electron interaction with crystal defects in wurtzite CdS
    • Authors: Orest Malyk; Volodymyr Rodych, Hryhoriy Il'Chuk
      Abstract: In the present paper the interaction of electrons with different types of defects with the potential of the limited action radius – polar and nonpolar optical phonons, piezoelectric and acoustic phonons, static strain centers, ionized and neutral impurities – in cadmium sulfide is considered. The dopant concentration in observed CdS crystals was in the limits of 5.5×1015 ÷ 1.1×1019 cm‐3. The dependences of the electron mobility and Hall factor on temperature in the interval 10 ÷ 400 K are investigated. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-03T09:14:59.069149-05:
      DOI: 10.1002/pssc.201510281
       
  • Peculiarities of CdS nanocrystal formation at annealing of a
           Langmuir‐ Blodgett matrix
    • Authors: Kirill Svit; Dmitry Protasov, Sergey Teys, Larisa Sveshnikova, Yakushev Maksim, Konstantin Zhuravlev
      Abstract: Formation and assembling of CdS nanocrystals (NC) on highly‐ordered pyrolytic graphite (HOPG) and on oxidized silicon substrates have been investigated by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). NC were initially formed within a Langmuir‐Blodgett (LB) matrix of cadmium behenate. The LB matrix was then removed by annealing in an ammonia atmosphere. It is shown that the NC self‐assembling is mainly determined by the LB matrix wetting properties. In case of wettable HOPG substrate homogeneous matrix evaporation occurs that leads to coarsening of the NC arrays as the main self‐assembly process. Otherwise, NC prepared on non‐wettable SiO2‐Si substrate demonstrate arrays formation determined by the LB matrix dewetting process. For the both cases, the influence of kinetic limitations connected with matrix evaporation rate on the self‐assembly process is observed. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-03-03T09:14:57.51281-05:0
      DOI: 10.1002/pssc.201510285
       
  • Observation of topological phase transition by terahertz photoconductivity
           in HgTe‐based transistors
    • Authors: A. M. Kadykov; C. Consejo, M. Marcinkiewicz, L. Viti, M. S. Vitiello, S. S. Krishtopenko, S. Ruffenach, S. V. Morozov, W. Desrat, N. Dyakonova, W. Knap, V. I. Gavrilenko, N. N. Mikhailov, S. A. Dvoretsky, F. Teppe
      Abstract: We have found the possibility to probe the magnetic field‐driven topological phase transition in HgTe‐based transistors by measuring their Terahertz photoconductivity response. At the critical magnetic field to which zero‐mode Landau levels cross, we have observed a pronounced photoconductivity peak independent on incident frequency and carrier concentration. Our results pave the way towards terahertz topological field effect transistors. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-25T03:13:04.847987-05:
      DOI: 10.1002/pssc.201510264
       
  • Molecular beam epitaxy of free‐standing bulk wurtzite
           AlxGa1‐xN layers using a highly efficient RF plasma source
    • Abstract: Recent developments with group III nitrides suggest AlxGa1‐xN based LEDs can be new alternative commercially viable deep ultra‐violet light sources. Due to a significant difference in the lattice parameters of GaN and AlN, AlxGa1‐xN substrates would be preferable to either GaN or AlN for ultraviolet device applications. We have studied the growth of free‐standing wurtzite AlxGa1‐xN bulk crystals by plasma‐assisted molecular beam epitaxy (PA‐MBE) using a novel RF plasma source. Thick wurtzite AlxGa1‐xN films were grown by PA‐MBE on 2‐inch GaAs (111)B substrates and were removed from the GaAs substrate after growth to provide free standing AlxGa1‐xN samples. Growth rates of AlxGa1‐xN up to 3 µm/h have been demonstrated. Our novel high efficiency RF plasma source allowed us to achieve free‐standing bulk AlxGa1‐xN layers in a single day's growth, which makes our MBE bulk growth technique commercially viable. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-25T03:13:03.548912-05:
      DOI: 10.1002/pssc.201510166
       
  • Towards industrialisation of GaN‐on‐Si based high brightness
           blue LEDs
    • Authors: Liyang Zhang; Wei Sin Tan, Simon Westwater, Antoine Pujol, Andrea Pinos, Samir Mezouari, Kevin Stribley, John Whiteman, John Shannon, Keith Strickland
      Abstract: The manufacturability of blue LED structures grown on 6‐inch Si (111) substrates is reported. The totally epi‐structure thickness is only 3.75 μm, which allows faster epitaxy process throughput and lower manufacturing costs. Well controlled strain engineering leads to a room temperature wafer bow of 0 ± 5 μm and a highly uniform photoluminescence wavelength standard deviation of 1.1 nm. XRD FWHM (002) and (102) are 380 and 390 arcsec, respectively. For a blue 1×1 mm2 vertical thin film die with silicone dome lens, the optical light output power of 563 mW at an operating voltage of 3.05 V is achieved at 350 mA. Excellent leakage current (IR) yield is achieved with over 95% of dies exhibiting IR < 0.1 μA at ‐5 V. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-25T03:13:02.54032-05:0
      DOI: 10.1002/pssc.201510168
       
  • Low pressure MOVPE growth and characterization of ZnTe homoepitaxial
           layers
    • Authors: Mitsuhiro Nishio; Katsuhiko Saito, Masakatsu Abiru, Eiichiro Mori, Yasuhiro Araki, Daichi Tanaka, Tooru Tanaka, Qixin Guo
      Abstract: The growth rate and photoluminescence (PL) spectrum of ZnTe homoepitaxial layer grown at a reactor pressure of 500 Torr by metalorganic vapor phase epitaxy have been clarified as a function of substrate temperature. An optimum substrate temperature for obtaining ZnTe layers with better PL property is determined by taking into account the growth rate behavior. Furthermore, the growth rate, PL spectrum, surface roughness and surface morphology of ZnTe layer have also been investigated by varying reactor pressure. With increasing reactor pressure, both the PL property and surface roughness of ZnTe layer are improved and subsequently become degraded, according as the growth rate increases monotonically and then shows saturated tendency. Change in the surface morphology of ZnTe layer with the increase of reactor pressure resembles that with the decrease of substrate temperature, probably due to the change from mass‐transport regime to surface kinetics one. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-25T03:13:00.722975-05:
      DOI: 10.1002/pssc.201510240
       
  • Luminescence dynamics of hybrid ZnO nanowire/CdSe quantum dot structures
    • Abstract: Colloidal CdSe quantum dots (QDs) functionalized with different organic linker molecules are attached to ZnO nanowires (NWs) to investigate the electron transfer dynamics between dots and wires. After linking the quantum dots to the nanowires, the photo‐induced electron transfer (PET) from the QDs into the NWs becomes visible in the PL transients by a decrease of dot luminescence decay time. The different recombination paths inside the QDs and the PET process are discussed in the framework of a rate equation model. Photoconductivity studies confirm the electron transfer by demonstrating a strong enhancement of the wire photocurrent under light irradiation into the dot transition. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-25T03:12:59.796045-05:
      DOI: 10.1002/pssc.201510253
       
  • Photoconductive properties of undoped and nitrogen‐doped ZnO single
           crystals in various ambiences
    • Authors: Takami Abe; Shuzo Takahashi, Shuhei Kamada, Akira Nakagawa, Tetsuya Chiba, Michiko Nakagawa, Shigeki Chiba, Yasuhiro Kashiwaba, Masahiro Daibo, Ikuo Niikura, Yasube Kashiwaba, Hiroshi Osada
      Abstract: The effects of ambiences on photoconductive properties of the Zn‐face of undoped ZnO and nitrogen‐doped ZnO (ZnO:N) single crystals are described. Oxygen (O2) gas affected the photocurrent spectra of the Zn‐face of both single crystals. The photocurrent was smallest in O2 gas and was largest in the vacuum ambience. The influence of ambience was very small in the visible light region but was large in the UV region. Regardless of the ambience, photocurrent of the Zn‐face of ZnO:N showed no sensitivity in the visible region. The decay time response of undoped ZnO and ZnO:N single crystals was also affected by the ambience. Decay time responses of both single crystals were fastest in O2 gas and were slowest in the vacuum ambience. The decay time response of the ZnO:N single crystal was faster than that of the undoped ZnO single crystal. These results showed that the effect of oxygen‐mediated surface recombination is strong in both large single crystals with very small surface‐to‐volume ratio and no grain boundary effect. The results also showed that doped nitrogen decreases the density of electron and hole traps near the surface region of the crystals. It is thought that steepness of band bending near the surface of a ZnO:N single crystal is smaller than that of an undoped ZnO single crystal. In conclusion, the Zn‐face of a ZnO:N single crystal sealed with O2 gas is useful as a photoconductive type UV sensor. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-25T03:12:58.907655-05:
      DOI: 10.1002/pssc.201510260
       
  • Unintentional nitrogen incorporation in ZnO nanowires detected by electron
           paramagnetic resonance spectroscopy
    • Authors: J. E. Stehr; W. M. Chen, N. K. Reddy, C. W. Tu, I. A. Buyanova
      Abstract: Unintentional incorporation of nitrogen in ZnO nanowires (NWs) grown by rapid thermal chemical vapor deposition is unambiguously proven by electron paramagnetic resonance spectroscopy. The nitrogen dopants are suggested to be provided from contaminations in the source gases. The majority of incorporated nitrogen atoms are concluded to reside at oxygen sites, i.e. in the atomic configuration of nitrogen substituting for oxygen (NO). The NO centers are suggested to be located in proximity to the NW surface, based on their reduced optical ionization energy as compared with that in a bulk material. This implies that the defect formation energy at the NW surface could be lower than its bulk value, consistent with previous theoretical predictions. The obtained results underline that nitrogen can be easily incorporated in ZnO nanostructures which may be of advantage for realizing p‐type conducting ZnO via N doping. On the other hand, the awareness of this process can help to prevent such unintentional doping in structures with desired n‐type conductivity. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-25T03:12:58.007038-05:
      DOI: 10.1002/pssc.201510261
       
  • Analysis of lags and current collapse in field‐plate AlGaN/GaN HEMTs
           with deep acceptors in a buffer layer
    • Authors: Naohiro Noda; Ryouhei Tsurumaki, Kazushige Horio
      Abstract: We make 2‐D transient simulations of field‐plate AlGaN/GaN HEMTs with a semi‐insulating buffer layer, where a deep acceptor above the midgap is considered. It is studied how the deep acceptor and the field plate affect lag phenomena and current collapse. It is shown that the drain lag and current collapse could be reduced by introducing a field plate, as in a case with a deep acceptor compensated by a deep donor in the buffer layer. This reduction occurs because electron trapping by the deep acceptors is weakened by the field plate. The dependence on insulator thickness under the field plate is also studied, suggesting that there is an optimum thickness of insulator to minimize the current collapse of AlGaN/GaN HEMTs. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-25T02:42:25.357108-05:
      DOI: 10.1002/pssc.201510156
       
  • Current density dependence of transition energy in blue InGaN/GaN MQW LEDs
    • Authors: F. Zhang; M. Ikeda, K. Zhou, Z. S. Liu, J. P. Liu, S. M. Zhang, H. Yang
      Abstract: In this paper we report on the transition energy in InGaN/GaN multiple quantum well (MQW) light emitting diodes (LEDs) under various injection current density from 2 A/cm2 to 200 A/cm2. Various effects including strain, quantum confined Stark effect (QCSE), screening effect by carriers, bandgap renormalization, Stokes‐like shift, band‐filling effect, and quantum levels in triangular quantum wells, are considered quantitatively and analyzed comprehensively. By comparing these effects altogether, we found that when the In‐content in quantum wells is fixed, the transition energy is mainly determined by QCSE and quantum level energy, between which QCSE overweighs the other. The transition energy shift with current density is also mainly governed by the screening effect of QCSE, with detailed competition between band tailing and filling. Additional effect, the coupling between adjacent quantum wells, is investigated in this paper. The coupling between quantum wells with various barrier thicknesses is compared. By calculating the wavefunctions self‐consistently, it is found that for InGaN/GaN MQWs with 5 nm quantum barriers (QBs), the coupling of electron wavefunctions leads to about 2 meV difference in transition energy. While for the MQWs with 3 nm QBs, the influence of electron wave‐function overlap on transition energy is 12.9 meV, which is more significant than that of 5 nm QB case. However, for hole wavefunctions, the coupling effect is too small to be considered, which is mainly due to the much larger effective mass. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-17T04:10:07.772128-05:
      DOI: 10.1002/pssc.201600005
       
  • Characterization of carrier concentration in ZnO nanowires by scanning
           capacitance microscopy
    • Abstract: Scanning capacitance microscopy (SCM) has been investigated on Ga doped ZnO staircase multi‐layers grown by molecular beam epitaxy (MBE) and ZnO NWs grown by chemical bath deposition (CBD). It is found that SCM data amplitude experiences a monotonic decrease with increasing Ga concentration from 2×1017 cm‐3 to 3×1020 cm‐3, indicating SCM being an appropriate technique for two dimensional dopant/carrier profiling in ZnO at nanoscale. For ZnO nanowires (NWs), a planariz‐ation process was developed based on dip‐coating of silica sol‐gel and chemical‐mechanical polishing. Then ZnO NWs were well detected from the silica matrix by SCM and the residual carrier concentration inside them was estimated through calibration method to be between 5×1017 cm‐3 and 2×1018 cm‐3. Finally, the result was compared with that obtained from conventional capacitance‐voltage (C‐V) measrement and their difference was discussed. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-17T04:10:06.765556-05:
      DOI: 10.1002/pssc.201510268
       
  • Role of electron‐phonon interaction in the temperature dependence of
           the phonon mode frequency in II‐VI compound alloys
    • Abstract: We present an experimental investigation of the temperature dependence of the TO‐phonon mode frequencies for the HgTe‐based II‐VI semiconductor solid solutions. In the case of the ternary Hg0.9Zn0.1Te solid solution was shown a discontinuity in the temperature dependence of the HgTe‐like TO‐mode and of the ZnTe‐like TO‐mode, similar to the Hg0.885Cd0.115Te system [Sheregii et al., Phys. Rev. Lett. 102, 045504 (2009)]. A generalization of the theoretical temperature shift of the phonon mode frequency as analytic equation is derived that includes both the anharmonic contribution and the electron‐phonon e‐p interaction which in this case is returnable the electron subsystem effect on the phonon one. Data show that our equation satisfactorily describes the temperature shift of both Hg0.885Cd0.115Te and Hg0.9Zn0.1Te containing Dirac point (Eg = Γ6–ΓΓ8 = 0) although one of the two constants describing the anharmonic shift of the HgTe‐like mode should be positive what is abnormal too. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-17T04:10:05.464365-05:
      DOI: 10.1002/pssc.201510236
       
  • Observation of in‐situ reciprocal lattice evolution of AlGaN/InGaN
           on Si (111) through GaN and AlN interlayers by RHEED and reflectance
    • Authors: Ankush Bag; Subhashis Das, Dhrubes Biswas
      Abstract: Due to the wave‐particle duality of high energy electron beam, RHEED describes a thin film surface through the interaction of reciprocal lattice rod (RLR) of the film. The RLR spacing of the crystal has been computed using RHEED streak spacing on a fluorescent screen. Present evolution study of RLR spacing has been performed for AlGaN/InGaN heterostructure on thick GaN buffer layer during plasma‐assisted molecular beam epitaxy. Effect of composition, strain and temperature on the crystal has been identified as the function of lattice spacing during the growth. The calibrated reflectivity of LED signal has also been employed to map the thickness of different growing epilayers. RLR spacing decreases for interlayer GaN as compared to AlN. Initially, the RLR spacing of GaN buffer decreases more as compared to interlayer GaN owing to its increased growth temperature after the interlayer AlN. The RLR spacing of GaN again gradually increases with decrement of growth temperature up to the InGaN channel layer. The InGaN RLR spacing decreases again which attributes to the relaxation of InGaN on GaN. Additionally, AlGaN reveals strained state to InGaN in combination with effect of high growth temperature. The phenomena result in additional decrement of lattice distance in reciprocal space. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-17T03:40:05.498282-05:
      DOI: 10.1002/pssc.201510202
       
  • Effect of electron blocking layers on the conduction and valence band
           profiles of InGaN/GaN LEDs
    • Abstract: In this paper we investigate the effect of including an electron blocking layer between the quantum well active region and the p‐type layers of a light emitting diode has on the conduction and valence band profile of a light emitting diode. Two light emitting diode structures with nominally identical quantum well active regions one containing an electron blocking layer and one without were grown for the purposes of this investigation. The conduction and valence band profiles for both structures were then calculated using a commercially available Schrödinger‐Poisson calculator, and a modification to the electric field across the QWs observed. The results of these calculations were then compared to photoluminescence and photoluminescence time decay measurements. The modification in electric field across the quantum wells of the structures resulted in slower radiative recombination in the sample containing an electron blocking layers. The sample containing an electron blocking layer was also found to exhibit a lower internal quantum efficiency, which we attribute to the observed slower radiative recombination lifetime making radiative recombination less competitive. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-17T03:40:04.634358-05:
      DOI: 10.1002/pssc.201510188
       
  • Improvement of thermal stability of p‐type ZnO:(Al,N) fabricated by
           oxidizing Zn3N2:Al thin films
    • Authors: Y. F. Wang; D. Y. Song, L. Li, B. S. Li, A. Shen, Y. Sui
      Abstract: The authors report the fabrication of p‐type ZnO thin films with improved thermal stability. The p‐type ZnO thin films were obtained by oxidizing Zn3N2:Al thin films in an oxygen ambient. Both Zn3N2:Al and Zn3N2 thin films were deposited on fused silica substrates at 100 °C by megnetron sputtering. X‐ray diffraction (XRD) measurements showed that the ZnO thin films obtained from by oxiding Zn3N2:Al, have preferred (002) orientation. On the other hand, ZnO films obtained by oxidizing Zn3N2 are polycrystalline. The optical band gap of ZnO (3.294 eV) obtained by annealing Zn3N2:Al thin films is narrower than that of the ZnO (3.31 eV) obtained by annealing Zn3N2. P‐type ZnO films were formed by annealing Zn3N2:Al at temperatures above 600 °C. A maximum hole density of 1.4 x 1016 cm‐3 was obtained in a film annealed at 800 °C. In contrast, only n‐type ZnO can be produced from oxidizing Zn3N2. Our results indicate that the Al can stabilize the nitrogen acceptors in ZnO thin films. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-09T02:40:20.636144-05:
      DOI: 10.1002/pssc.201510164
       
  • RT ZnSe‐based lasers and laser arrays pumped by low‐energy
           electron beam
    • Authors: M. M. Zverev; S. V. Sorokin, N. A. Gamov, E. V. Zhdanova, V. B. Studionov, I. V. Sedova, S. V. Gronin, S. V. Ivanov
      Abstract: The properties of an electron‐beam‐pumped ZnSe‐based laser array consisting of 6 one‐dimensional arrays, each comprising 10 single laser elements, have been studied. The peak output power up to 80‐100 W at room temperature in “true” green (λ = 547 nm) spectral range has been demonstrated by using for pumping electrons with the accelerating energy as low as 5.6 keV. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-09T02:40:19.821422-05:
      DOI: 10.1002/pssc.201510251
       
  • Evidence of exchange interaction of localized carriers and transition
           metals in diluted II‐VI nanostructures: ODMR study
    • Authors: P. G. Baranov; N. G. Romanov, D. O. Tolmachev, A. S. Gurin, B. R. Namozov, Yu. G. Kusrayev, G. Karczewski, S. Orlinskii, C. De Mello Donega, J. Schmidt
      Abstract: Optically detected magnetic resonance study of (CdMn)Te/(CdMg)Te quantum wells allowed to reveal the formation of exchange‐coupled complexes consisting of Mn ions and localized holes in quantum wells with excess hole concentration and the directional electron tunneling towards wider wells in multiple quantum well structures. The existence of a distribution of Mn‐hole complexes that differ in a number of Mn ions interacting with a localized hole is justified. In colloidal cobalt doped ZnO nanocrystals, several nm in diameter, the interaction between the magnetic ions and the shallow donor electron in the confined system of ZnO quantum dots has been revealed. Direct evidence of interaction of Co ions with the interstitial Li shallow donor in the ZnO nanocrystal core and hyperfine coupling with 1H in the quantum dot shell have been demonstrated. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-09T02:40:18.924974-05:
      DOI: 10.1002/pssc.201510249
       
  • p‐d charge transfer excitons in Zn1‐xNixO under inner shell
           excitation
    • Authors: V. N. Churmanov; V. I. Sokolov, N. B. Gruzdev, V. Yu. Ivanov, V. A. Pustovarov
      Abstract: The paper presents results of the study of two narrow luminescence lines I1 and I2 at the energies of 3.339 and 3.393 eV respectively in solid state solutions Zn1‐xNixO. The luminescence spectroscopy with a sub‐nanosecond time resolution upon selective photoexcitation in the energy range of the inner shell Zn M‐edge absorption was used to promote the earlier proposed mechanism of the I1 and I2 lines origin. Photoluminescence spectra of solid state solutions Zn1‐xNixO at fast and slow time windows under soft X‐ray excitation are discussed. The doublet of I1 and I2 lines is believed to arise due to the radiative annihilation of p‐d excitons. Different possible mechanisms of emergence of two narrow luminescence lines I1 and I2 in solid state solutions Zn1‐xNixO are considered. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-09T02:40:18.016128-05:
      DOI: 10.1002/pssc.201510245
       
  • Neutronographic characterization of II‐VI cubic crystals highly
           doped by 3d ions: on possible tendencies to structure rearrangements in
           the sphalerite crystal lattice
    • Abstract: Fine features of the crystal structure of Zn0.9Ni0.1S, Zn0.9V0.1Se, Zn0.95Fe0.05Se semiconductor cubic single crystals have been characterized by neutron scattering at room temperature. It has been revealed that neutron‐diffraction scans of the single crystals, in addition to intense Bragg reflections of face‐centered cubic phase, contain a complex system of diffuse scattering maxima, included superstructure reflections. The superstructure diffuse maxima are found placed on reciprocal lattice knots corresponding with the wave vectors q = (1/3 1/3 1/3) 2π/ac (ac is the cubic lattice parameter), which is interpreted as a manifestation of pretransition state. It is proposed that the revealed destabilized structure state means pretransition of reconstructive structure transformation from the cubic phase to the hexagonal phase. Strong perturbations caused by 3d ions doping lead to a collective response of the cubic lattice of the II‐VI matrices, displacing atomic planes in shears, and tend to induce the transformation. Such a complicated structure state determines nonuniform deformation field supporting possibilities to form long‐wave superstructures. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-09T02:40:17.228333-05:
      DOI: 10.1002/pssc.201510231
       
  • Magnetic phase transitions in ZnO doped by transition metals
    • Authors: Shavkat Yuldashev; Vadim Yalishev, Ziyodbek Yunusov, Younghae Kwon, Tae Won Kang
      Abstract: In this work we present the results on experimental study of magnetic phase transitions in ZnO thin films doped by Mn and Co by using the thermal diffusivity and specific heat measurements. The inverted lambda‐shaped peaks observed in the temperature dependencies of the thermal diffusivity demonstrate the existence of the second order phase transitions in these samples. The magnetic entropy derived from the specific heat gives the number of magnetic ions involved in the magnetic ordering. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-09T02:40:16.367901-05:
      DOI: 10.1002/pssc.201510221
       
  • Application of indium tin oxide to the p‐cladding layers of
           yellow/green II‐VI compound semiconductor laser diode structures on
           InP substrates
    • Authors: Koji Fukushima; Tomohiro Shiraishi, Ryohei Kobayashi, Katsumi Kishino, Ichirou Nomura
      Abstract: The application of indium tin oxide (ITO) as the p‐cladding layer of II‐VI compound semiconductor laser diodes (LDs) on InP substrates was investigated. The waveguide analysis of the LD structures revealed that the optical confinement effect around the active layer was obviously improved by changing the p‐cladding layer from the conventional MgSe/BeZnTe superlattice to ITO. For example, the estimated optical confinement factors were 0.15 and 0.27 for the conventional and ITO LD structure, respectively, when the emission wavelength was 580 nm. In addition, we investigated optimum LD structures, considering the optical and carrier confinements at the active layer. In experiments, light emitting devices with an ITO layer were fabricated on InP substrates via molecular beam epitaxy and radio‐frequency (RF) magnetron sputtering. Yellow emissions at 582 nm were observed by current injections at room temperature. These results indicate that ITO is a promising p‐cladding layer material for II‐VI LDs on InP substrates. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-09T02:40:13.832463-05:
      DOI: 10.1002/pssc.201510254
       
  • Growth and characterization of ZnCdSe/ZnCdMgSe two‐color quantum
           well infrared photodetectors
    • Authors: Guopeng Chen; Yasin Kaya, Arvind Pawan Ravikumar, Maria C. Tamargo, Claire F. Gmachl, Aidong Shen
      Abstract: The authors report, for the first time, the new two‐color quantum well infrared photodetectors (QWIPs) from a non‐III‐V semiconductor material system. The samples were grown on InP substrate by molecular beam epitaxy. X‐ray diffraction and photoluminescence measurements showed high structural and optical quality of the samples. Two intersubband (ISB) absorption peaks in two different wavelength regions are observed in Fourier transform infrared measurements. The two‐color photodetectors can be turned on separately or simultaneously in the two spectral regions. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-09T02:40:12.681193-05:
      DOI: 10.1002/pssc.201510257
       
  • Application of the difference spectroscopy for studying of complex
           acceptors in CdTe
    • Authors: Victor Bagaev; Vladimir Krivobok, Sergey Nikolaev, Evgeny Onischenko, Anna Pruchkina
      Abstract: Wavelength modulation of the excitation source combined with the analysis of the differential PL signal have been applied to studying of electronic spectra of acceptors in compensated CdTe:Cl, CdTe:Ag,Cl single crystals. For the Cl‐related complex acceptor with an activation energy of ∼121 meV (A‐center), the energies of eight excited states are measured. In the case of tetrahedral AgCdacceptor the splitting of 2P3/2 (Γ8) and 2S3/2 (Γ8) states has been revealed for AgCd centres located at a short distances (5‐7 nm) from a hydrogen‐like donor (ClTe). A method allowing a simple symmetry test for acceptors in a diverse zinc‐blende compound semiconductor is proposed. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-09T02:40:11.888378-05:
      DOI: 10.1002/pssc.201510262
       
  • ZnTe layers on R ‐ and S ‐plane sapphire substrates
    • Abstract: ZnTe epilayers were grown on R ‐plane ($ 10 \bar 1 4 $) and S ‐plane ($ 10 \bar 1 1 $) sapphire substrates by molecular beam epitaxy, and the crystal orientation and the optical property were studied. The crystal orientation of ZnTe layers on sapphire substrates was studied using X‐ray diffraction pole figure measurements. It was confirmed that (111)‐oriented domains were formed on the R ‐plane as well as on the S ‐plane substrate. Layers grown on R ‐plane exhibited higher film quality. From the low‐temperature photoluminescence, emissions caused by ZnTe exciton were observed. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-09T02:40:11.005934-05:
      DOI: 10.1002/pssc.201510265
       
  • Electron spin flip Raman spectroscopy of the diluted magnetic
           
    • Authors: A. G. Knapp; S. Petznick, F. Jansson, M. Wiemer, M. Hetterich, F. Gebhard, S. D. Baranovskii, P. J. Klar, J. Geurts
      Abstract: In n‐doped (Zn,Mn)Se, the (s,d) exchange influences the ground state level of the donor‐bound electrons in an external B‐field, depending on their local Mn environment. Due to the statistical Mn arrangement, this should induce a broadening of the donor energy distribution, inducing a magneto‐resistance in transport, and also a broadening of the energy distribution of donor‐bound excitons (D0,X). We have investigated this broadening for Zn0.94Mn0.06Se:Cl (n= 4.5×1017 cm‐3) by electronic spin flip Raman spectroscopy (ESFRS) on the donor electrons. Utilizing the resonant enhancement of the ESFRS intensity upon resonance of the laser light with (D0,X), we actually observe a significant broadening of the ESFRS resonance profiles with increasing B‐field, up to 11.5 meV (FWHM) for B = 5 T. Furthermore we detect a second resonance profile contribution, whose FWHM shows a much weaker B‐field dependence. We assign this contribution to a resonance mediated by the free‐exciton (X0). Our Raman results agree very well with magneto‐transport results at the same sample. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-09T02:40:10.240025-05:
      DOI: 10.1002/pssc.201510267
       
  • MOCVD growth of ZnO nanowires on Ni‐W metallic substrates
    • Abstract: Here we investigate the possibility to grow ZnO nanowires on (100) textured Ni‐W substrates by MOCVD at 850 °C. Due to the oxidation of Ni, direct growth of ZnO nanowires on those metallic substrates was not achieved whereas it was easily obtained on sapphire in the same conditions. Therefore, a study of a ZnO buffer layer grown at low temperature was performed in order to prevent the NiO formation. The morphology and the crystallographic orientation of the as‐grown interfacial layers were characterized by scanning emission microscopy (SEM) and XRD diffraction, and are shown to depend on the growth temperature. Subsequently, the growth of ZnO nanowires was carried out on ZnO buffer/Ni‐W pseudo‐substrates. The SEM observations reveal the growth is not homogeneous and depends on the grain orientation. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-03T07:10:15.299919-05:
      DOI: 10.1002/pssc.201510308
       
  • Resonant photoluminescence of a positively charged Mn‐doped quantum
           dot
    • Abstract: We probe the spin dynamics of an individual magnetic atom (Mn) coupled to carriers in a positively charged quantum dot using resonant photoluminescence. We demonstrate that a p‐doped CdTe/ZnTe quantum dot containing a single Mn atom forms an ensemble of optical Λ systems which can be addressed independently. Performing resonant optical pumping experiment and auto‐correlation of the resonant photoluminescence, we show that these Λ systems are connected through inefficient forbidden spin‐flips. We demonstrate that the spin dynamics of X+‐Mn under resonant excitation is mainly controlled by the electron‐Mn interaction. This coherent dynamics is directly observed in the time domain and is shown to be highly sensitive to the local strain at the Mn location. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-03T07:10:09.451634-05:
      DOI: 10.1002/pssc.201510248
       
  • Crystallographic and optical characterizations of Ag(Ga,Al)Te2 layers
           grown on c ‐plane sapphire substrates by closed space sublimation
    • Authors: Aya Uruno; Yuji Takeda, Tomohiro Inoue, Masakazu Kobayashi
      Abstract: Ag(Ga,Al)Te2 layers were grown by the closed space sublimation method on c ‐plane sapphire substrates. The source used was AgAlTe2/AgGaTe2 mixture or AgAlTe2/Ga2Te3 mixture. The crystallographic property of Ag(Ga,Al)Te2 layers was analyzed by X‐ray diffraction (XRD). XRD spectra of layers exhibited very strong 112 diffraction peaks regardless of the variation of the source material mixture. In addition to crystallographic characterizations, optical properties of the Ag(Ga,Al)Te2 layer were evaluated through transmittance measurements. The bandgap energy was decreased when the source mole ratio of Al to Ga was decreased. It was revealed that control regulation of x composition of Ag(Ga1‐x,Alx)Te2 was feasible by varying the source mole ratio Al/(Ga+Al). (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-03T07:10:08.461123-05:
      DOI: 10.1002/pssc.201510269
       
  • Quantum confined Stark effect of polar and non‐polar ZnO/ZnMgO
           quantum wells grown by MBE
    • Authors: Tomoki Abe; Tatsuya Motoyama, Masaya Yamamoto, Atsushi Yamamoto, Shohei Iwagashita, Hirofumi Kasada, Koshi Ando, Kunio Ichino
      Abstract: We have investigated quantum confined Stark effects of polar (O‐polar) and non‐polar ZnO/ZnMgO quantum wells (QWs) by electroabsorption (EA) spectroscopy. The ZnO/ZnMgO QWs were grown by plasma assisted molecular beam epitaxy (PA‐MBE). The ZnO/ZnMgO QWs were grown on c‐plane sapphire for polar ZnO QWs, and on r‐plane sapphire for non‐polar ZnO QWs, respectively. The polar ZnO/ZnMgO QWs exhibited a blue‐shift of 20 meV in excitonic transition energy by applying external bias at room temperature. This blue‐shift is due to reverse quantum confined Stark effect (QCSE) in a piezo electric‐field induced QW structures of wurtzite ZnO/ZnMgO QWs with c‐axis orientation. We confirmed a large red‐shift of 29 meV for non‐polar ZnO/ZnMgO QWs. This energy shift is originated from normal QCSE in the flat potential QWs without built‐in piezo electric‐field. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-03T07:10:07.589609-05:
      DOI: 10.1002/pssc.201510272
       
  • Contents: Phys. Status Solidi C 5–6/2016
    • Pages: 171 - 176
      PubDate: 2016-05-25T02:24:51.916617-05:
      DOI: 10.1002/pssc.201670125
       
  • Nitride Semiconductors
    • Authors: Guoyi Zhang; Bo Shen, Guoyi Zhang, Tongjun Yu, Ning Tang, Xuelin Yang, Shunfeng Li
      Pages: 177 - 180
      Abstract: The 11th International Conference on Nitride Semiconductors (ICNS‐11) was held at Beijing International Convention Center during August 30 to September 4, 2015. The ICNS conference series is a premier platform for presenting research results in group III‐nitride semiconductors. The 11th one was the latest following the first conference held in Nagoya, Japan (TWN'95); the second in Tokushima, Japan (ICNS‐2); the third in Montpellier, France (ICNS‐3); the fourth in Denver, USA (ICNS‐4); the fifth in Nara, Japan (ICNS‐5); the sixth in Bremen, Germany (ICNS‐6); the seventh in Las Vegas, USA (ICNS‐7); the eighth in Jeju, Korea (ICNS‐8); the ninth in Glasgow, UK (ICNS‐9); and the tenth in Washington D.C. USA (ICNS‐10). The conference was very well attended with 821 attendees from 33 countries and areas, who had enjoyed a nice summer week in Beijing. A total of 733 abstracts were submitted to the conference, making 191 oral and 484 poster presentations. The Nitride Semiconductor field continues to grow and diversify, and as a result, the conference series ran four parallel sessions. The conference was divided into 44 different symposia, covering the entire spectra of III‐nitride semiconductor research and applications. Combining with 3 ramp sessions, all the contributors to this conference shared the general trends appearing in nitride semiconductor community, including the steady advancements in growth of GaN and AlN bulk crystals, greater attentions towards electronic devices, a movement from lateral to vertical devices, much progress in UV devices, more concern about point defects, and atomic level analysis on homogeneity or segregation of InGaN alloys. The organizers are particularly grateful to Nobel Prize laureates Hiroshi Amano and Shuji Nakamura for their great support to this conference. We are also very grateful to all members of the conference committees and invited speakers. We would especially like to acknowledge the sponsors and agencies for their financial support. Thanks also to the 38 exhibitors who participated in the meeting. Finally, we especially want to express our great appreciation to Overseas Exchange Center of Peking University and Beijing International Conference Center. Altogether 109 submissions were received for the conference proceedings to be published in the journal of physica status solidi, based on their standard evaluation procedures. Among them, 76 articles have been accepted for publication in this special volume, with 28 being accepted for special sections in Phys. Status Solidi A and Phys. Status Solidi B. We are grateful to the editorial support provided by Stefan Hildebrandt, Julia Hübner, Irina Juschak and their team in bringing the proceedings together. Finally, we thank all those who attended and contributed to making ICNS‐11 such an enjoyable and successful conference and look forward to meeting you all again in Strasbourg at ICNS‐12 in 2017.
      PubDate: 2016-05-25T02:24:47.045393-05:
      DOI: 10.1002/pssc.201670126
       
  • Growth of compressively‐strained GaN films on Si(111) substrates
           with thick AlGaN transition and AlGaN superlattice buffer layers
    • Authors: Lei Pan; Xun Dong, Jinyu Ni, Zhonghui Li, Qiankun Yang, Daqing Peng, Chuanhao Li
      Pages: 181 - 185
      Abstract: In this paper, crack‐free GaN films with step‐graded AlGaN transition layer and AlGaN superlattice layer as buffer layers were grown on Si(111) substrate by metal‐organic chemical vapor deposition(MOCVD). The combination of both buffers effectively improves the properties of GaN layer. With the optimization of the buffer structures, high quality compressively‐strained GaN layers with thickness up to 3.6 μm have been obtained on Si(111) substrates (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-01-29T05:30:18.769418-05:
      DOI: 10.1002/pssc.201510175
       
  • Semi‐polar (11‐22) GaN grown on patterned (113) Si substrate
    • Authors: Xiang Yu; Yaonan Hou, Shuoheng Shen, Jie Bai, Yipin Gong, Yun Zhang, Tao Wang
      Pages: 190 - 194
      Abstract: An epitaxial growth technic has been developed to synthesize semi‐polar (11‐22) GaN on (113) Si substrate with inverted‐pyramid patterns. The reaction between Ga and Si substrate has been successfully solved by simply depositing a thin SiO2 layer on selective regions of the substrate before growth. High quality semi‐polar (11‐22) GaN‐on‐Si with a smooth surface has been obtained after delicately tuning growth conditions. Based on the scanning electron microscopy and x‐ray diffraction characterizations, a model has been well established to illuminate the growth process. Due to the very low density of defects confirmed by transmission electron microscopy, our sample demonstrates an excellent optical property, which is promising for efficient optoelectronic devices using GaN‐on‐Si configuration. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-01-27T02:40:10.97402-05:0
      DOI: 10.1002/pssc.201510209
       
  • Growth mode of nitride semiconductors on nano‐patterned sapphire
           substrates by molecular beam epitaxy
    • Pages: 195 - 199
      Abstract: In this paper we report on the growth mode by plasmaassisted MBE of nitride films on nano‐patterned sapphire substrates. Such substrates were fabricated using nano‐sphere and nano‐imprint lithographies, which led to cone‐and cylinder‐shaped patterns respectively. The data indicate that the pillars of the patterned substrate act a seeds for the subsequent growth and that the growth proceeds through the formation of a fully faceted pyramidal top surface. As the growth proceeds to more than 3 µm, the growth is dominated by the lateral growth of the top (0001) facets since the fluxes of the precursors on the inclined facets are lower. Eventually, these hexagonal (0001) facets coalesce leading to a continuous film with a smooth surface morphology. This multifaceted growth mode at the initial stages has the potential of lateral expulsion of threading dislocation by the inclined facets leading to nitride pillars with minimum number of threading dislocations. Cathodoluminescence measurements indicate significant increase in the emission intensity from the films grown on the nanopatterned sapphire substrates, compared to the emission from the films grown on the un‐patterned sapphire substrates. This increase is partly due to improvements in light extraction and partly to the improved crystalline quality of the films. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-03T06:40:21.042261-05:
      DOI: 10.1002/pssc.201510212
       
  • Effect of QW growth temperature on the optical properties of blue and
           green InGaN/GaN QW structures
    • Pages: 209 - 213
      Abstract: In this paper we report on the impact that the quantum well growth temperature has on the internal quantum efficiency and carrier recombination dynamics of two sets of InGaN/GaN multiple quantum well samples, designed to emit at 460 and 530 nm, in which the indium content of the quantum wells within each sample set was maintained. Measurements of the internal quantum efficiency of each sample set showed a systematic variation, with quantum wells grown at a higher temperature exhibiting higher internal quantum efficiency and this variation was preserved at all excitation power densities. By investigating the carrier dynamics at both 10 K and 300 K we were able to attribute this change in internal quantum efficiency to a decrease in the non‐radiative recombination rate as the QW growth temperature was increased which we attribute to a decrease in incorporation of the point defects. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-03T06:40:23.717017-05:
      DOI: 10.1002/pssc.201510187
       
  • Effect of NH3 flow on incorporation efficiency of Al composition and
           reduction of surface donor states in AlGaN grown by MOVPE
    • Authors: Tao Gao; Ruimin Xu, Dongguo Zhang, Zhonghui Li, Daqing Peng, Xun Don, Tangsheng Chen
      Pages: 214 - 216
      Abstract: We have studied the effect of various ammonia (NH3) flow rates on AlGaN film grown on GaN using c‐plane sapphire as substrate by metal organic chemical vapour deposition. The influences of NH3 flow on the species diffusion anisotropy of thick AlGaN films were investigated by scanning electron microscopy, atomic force microscopy and high‐resolution X‐ray diffraction measurements. It is demonstrated that, in addition to the larger NH3 flow, growth of the AlGaN epilayer under the same trimethylaluminum (TMAl) flow condition as others is a critical factor for less micro‐cracks. The results of X‐ray double crystal diffraction showed that the AlGaN films with larger ammonia flow exhibited lower Al content and smaller (0002) rocking curve width, and while NH3 flow rate reached 23 liter per minute, a (0002) rocking curve width of 295 arcsecond was reached. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-09T02:40:14.811803-05:
      DOI: 10.1002/pssc.201510185
       
  • Energetics and core structure of the undissociated basal screw dislocation
           in wurtzite GaN
    • Authors: I. Belabbas; J. Chen, G. Nouet
      Pages: 221 - 224
      Abstract: We have carried out computer atomistic simulations, based on Density Functional Theory, to investigate energetics and core structure of the undissociated basal screw dislocation in wurtzite GaN. Our calculations enabled us to establish the energetic hierarchy of two stable core configurations. The shuffle core configuration, which is formed by fully coordinated atoms, was demonstrated to be more energetically favorable than the glide configuration, which exhibits sp2‐like hybridization. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-03T06:40:24.611972-05:
      DOI: 10.1002/pssc.201510177
       
  • Room temperature PL efficiency of InGaN/GaN quantum well structures with
           prelayers as a function of number of quantum wells
    • Pages: 248 - 251
      Abstract: We report on the effects of varying the number of quantum wells (QWs) in an InGaN/GaN multiple QW (MQW) structure containing a 23 nm thick In0.05Ga0.95N prelayer doped with Si. The calculated conduction and valence bands for the structures show an increasing total electric field across the QWs with increasing number of QWs. This is due to the reduced strength of the surface polarisation field, which opposes the built‐in field across the QWs, as its range is increased over thicker samples. Low temperature photoluminescence (PL) measurements show a red shifted QW emission peak energy, which is attributed to the enhanced quantum confined Stark effect with increasing total field strength across the QWs. Low temperature PL time decay measurements and room temperature internal quantum efficiency (IQE) measurements show decreasing radiative recombination rates and decreasing IQE, respectively, with increasing number of QWs. These are attributed to the increased spatial separation of the electron and hole wavefunctions, consistent with the calculated band profiles. It is also shown that, for samples with fewer QWs, the reduction of the total field across the QWs makes the radiative recombination rate sufficiently fast that it is competitive with the efficiency losses associated with the thermal escape of carriers. (© 2016 The
      Authors . Phys. Status Solidi C published by WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-01-27T02:30:07.492639-05:
      DOI: 10.1002/pssc.201510180
       
  • Investigating efficiency droop in InGaN/GaN quantum well structures using
           ultrafast time‐resolved terahertz and photoluminescence spectroscopy
           
    • Authors: Aniela Dunn; Ben F. Spencer, Samantha J. O. Hardman, Darren M. Graham, Simon Hammersley, Matthew J. Davies, Phil Dawson, Menno J. Kappers, Rachel A. Oliver, Colin J. Humphreys
      Pages: 252 - 255
      Abstract: The mechanisms governing efficiency droop in an In0.18Ga0.82N/GaN multiple quantum well structure were investigated using a combination of ultrafast time‐resolved terahertz and photoluminescence spectroscopy. From excitation fluence dependent studies, a reduction in the room temperature photoluminescence efficiency to 3% of its maximum value was observed for an excitation fluence of 0.96 mJcm‐2. A correlation was found between the onset of efficiency droop and the emergence of a peak on the high‐energy side of the quantum well emission with a 1/e decay time of 19.6 ps. These characteristics were attributed to the saturation of localised states and the population of higher energy delocalised states. Time‐resolved studies revealed different scaling behaviours between the terahertz and photoluminescence decay dynamics, suggesting that the saturation of localised hole states may be playing a part in the onset of efficiency droop. (© 2016 The
      Authors . Phys. Status Solidi C published by WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-03T06:40:21.957191-05:
      DOI: 10.1002/pssc.201510193
       
  • Model of photoluminescence temperature dependence in GaN/AlN quantum dot
           structures
    • Authors: Ivan A. Aleksandrov; Vladimir G. Mansurov, Vladimir I. Vdovin, Konstantin S. Zhuravlev
      Pages: 289 - 291
      Abstract: Temperature dependence of photoluminescence intensity and lifetime of GaN/AlN quantum dots have been investigated and compared a theoretical model. Experimental photoluminescence lifetime is mainly determined by radiative process at low temperatures, but somewhat differs from the calculated radiative lifetime at room temperature. This difference corresponds to decrease in the nonradiative lifetime with temperature. Dependence of the nonradiative lifetime in GaN/AlN quantum dots on temperature and emission wavelength has been described by calculations assuming that the nonradiative recombination is caused by tunneling of carriers from quantum dots to nonradiative recombination centers. The tunneling probability has been calculated in the configuration coordinate model using the zero‐radius potential approximation. Temperature dependence of photoluminescence intensity of quantum dots does not follow the temperature dependence of the ratio of the photoluminescence lifetime to the radiative lifetime. Nonradiative recombination of carriers generated in a wetting layer has been taken into account to describe the temperature dependence of the photoluminescence intensity. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-01-27T02:40:08.227658-05:
      DOI: 10.1002/pssc.201510199
       
  • Effect of an ITO current spreading layer on the performance of InGaN MQW
           solar cells
    • Authors: J. Bai; M. Athanasiou, T. Wang
      Pages: 297 - 300
      Abstract: InGaN‐based solar cells have been investigated through fabrication with and without using an indium‐tin‐oxide (ITO) current spreading layer (CSL). For the devices with a planar top surface, utilization of the ITO CSL leads to enhanced performance under 1 sun air‐mass 1.5 global spectrum illumination. In contrast, when surface‐texturing is applied to significantly improve the light absorption, the efficiency of the device without using the ITO CSL is higher compared to the one with the ITO. Furthermore, measurements on reflectance of the corresponding surfaces and transmission of the ITO CSL are carried out. The influence of the ITO CSL has been discussed in terms of surface reflection, the light loss due to the ITO CSL shading and the power loss associated with the absence of the ITO CSL. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-01-29T05:30:16.951925-05:
      DOI: 10.1002/pssc.201510171
       
  • Theoretical analysis of the influence of band tail defects on PIN InGaN
           solar cells
    • Authors: Baozhu Wang; Yan Feng, Lizhi Meng, Min Wang, Hongling Xiao, Xiaoliang Wang
      Pages: 301 - 303
      Abstract: InGaN solar cells have higher conversion efficiency than traditional Si based solar cells. However, efficiency of experimental InGaN solar cell is lower than expected. There are still several problems, such as the structure design of InGaN solar cells, the quality of InGaN materials, need to be discussed and solved. Thus, the researches of structure design and defect effects are important for the implications of InGaN solar cells. The performance of p‐GaN/i‐InxGa1–x/n‐GaN solar cells with different In content is simulated by AMPS‐1D. It is found that the optimum efficiency of p‐GaN/i‐InxGa1–xN/n‐GaN solar cells is 8.9% when the In content is 0.26. The p‐GaN/i‐In0.26Ga0.74/n‐GaN solar cells with band tail defects are simulated. The simulated results show the efficiency decreases with the increase of the E‐character. And the efficiency decreases sharply from 8.30% to 7.19% when the capture cross section is 10–14 cm–2. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-01-27T02:40:07.095308-05:
      DOI: 10.1002/pssc.201510198
       
  • High‐resistance GaN‐based buffer layers grown by a
           polarization doping method
    • Authors: Lian Zhang; Yun Zhang, Hongxi Lu, Junxi Wang, Jinmin Li
      Pages: 307 - 310
      Abstract: A high‐resistance buffer layer is critical for GaN‐based high electron mobility transistors (HEMTs) to suppress the drain leakage current and pre‐mature device breakdown. A typical method to obtain the HR buffer layers is the acceptor impurity doping that is able to provide holes to compensate the background electrons in the buffer layers. However, the intentional doped acceptor impurities such as Mg, Fe and C will result in current collapse in GaN‐based HEMTs. To address this issue, in this work, we employed a polarization doping method of holes by Al‐composition grading instead of the acceptor impurity doping. The sheet resistance of the GaN‐based buffer layer significantly increased due to the holes generated by the polarization field. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-01-27T02:30:08.801667-05:
      DOI: 10.1002/pssc.201510181
       
  • MOCVD growth of DH‐HEMT buffers with low‐temperature AlN
           
    • Authors: Ming Zhao; Hu Liang, Prem Kumar Kandaswamy, Marleen Van Hove, Rafael Venegas, Evi Vranken, Paola Favia, Annelies Vanderheyden, Danielle Vanhaeren, Yoga Nrusimha Saripalli, Stefaan Decoutere, Robert Langer
      Pages: 311 - 316
      Abstract: In this work, we have systematically investigated the technique of low‐temperature AlN interlayer in MOCVD growth of double heterojunction high‐electron‐mobility transistors buffer stacks on 200 mm Si (111) substrates. We have demonstrated that a continuous compressive stress can be maintained by insertion of interlayers which compensated a large tensile stress during cooling for a thick buffer. This eventually led to a low wafer bow and a good surface quality that enabled wafers with full device stack meeting the specifications for processing in our 200 mm CMOS pilot line. We also demonstrated at both forward and reverse bias conditions a significantly improved vertical buffer breakdown voltage (which is defined at a leakage current of 1 µA/mm2 in the present work) of >500 V at 25 °C and >300 V at 150 °C, respectively. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-01-27T02:40:12.021243-05:
      DOI: 10.1002/pssc.201510280
       
  • Capacitance‐voltage characteristic of Ga‐ and N‐polar
           AlGaN/GaN HEMTs
    • Authors: Daqing Peng; Zhonghui Li, Chuanhao Li, Dongguo Zhang, Liang Li, Xun Dong, Lei Pan, Weike Luo
      Pages: 317 - 320
      Abstract: Ga‐ and N‐polar AlGaN/GaN HEMTs were designed and epitaxially grown on Si‐ and C‐face SiC substrates by MOCVD. The Capacitance‐voltage characteristics of the two structures were investigated by C‐V profile and drift‐diffusion simulations. The N‐polar structure shows double channels, while the electron concentration in the second channel is one order of magnitude lower than that in the first channel. Energy band diagrams and charge distributions were studied. The second channel is formed in AlN/AlGaN interface with electrons spilling over from the first channel when adequate negative voltage was applied on the schottky contact. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-09T02:40:15.561862-05:
      DOI: 10.1002/pssc.201510195
       
  • Study of threshold voltage instability in E‐mode GaN MOS‐HEMTs
    • Authors: Ferdinando Iucolano; Antonino Parisi, Santo Reina, G. Meneghesso, Alessandro Chini
      Pages: 321 - 324
      Abstract: In this work, the threshold instability in E‐mode GaN MOS‐HEMTs was investigated. In particular, the shift of VTH as a function of the applied positive gate voltage during device characterization was monitored, resulting in positive VTH shifts up to 1 V. A complete VTH recovery required more than one day of unbiased storage, but a partial recovery of the observed VTH shift was observed after few seconds. These results could be related to different positions of trap states: fast states, localized at the dielectric/GaN interface and slow states, the traps inside the dielectric layer. Moreover, VTH shift of 0.2 and 0.8 V for fast and slow states, respectively, was obtained. To gain insight into the physical mechanism involved in the observed phenomena, numerical simulation were also carried out. A VTH shift was obtained adding the interface states. Moreover, three different distributions of traps were compared. In particular, the concentration of filled traps was monitored to understand the impact of the distribution on the electrical behaviour. An increment in filled trap concentration at the increasing of the applied VGS, which in turns correlates with experimentally evaluated device behaviour, was obtained if the distribution of traps states is also above the GaN conduction band energy. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-01-29T05:30:21.177644-05:
      DOI: 10.1002/pssc.201510191
       
  • Threshold voltage engineering in GaN‐based HEMT by using La2O3 gate
           dielectric
    • Authors: Minhan Mi; Yunlong He, Bin Hou, Meng Zhang, Jincheng Zhang, Chong Wang, Xiaohua Ma, Yue Hao
      Pages: 325 - 327
      Abstract: In this paper, we presented AlGaN/GaN MIS‐HEMT with a 6‐nm ALD La2O3 as gate insulator. The gate leakage current had been greatly reduced at both positive and negative bias by using La2O3 gate dielectric. Threshold voltage for MIS‐HEMT moved +1 V toward positive direction compared with the Schottky gate HEMT (HEMT) demonstrating the negatively fixed charges at La2O3/AlGaN interface. Besides, the transconductance of MIS‐HEMT was not degraded. The stability of fixed and trap state introduced by La2O3 gate dielectric was discussed. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-01-29T05:30:17.823511-05:
      DOI: 10.1002/pssc.201510174
       
  • Impact of interface traps on switching behavior of normally‐OFF
           AlGaN/GaN MOS‐HEMTs
    • Authors: Yuanyuan Shi; Qi Zhou, Yang Jin, Bowen Chen, Wanjun Chen, Wei Huang, Bo Zhang
      Pages: 328 - 331
      Abstract: In this paper, we report an experimental observation of the two‐stage turn‐on characteristic in normally‐OFF Al2O3/GaN metal‐oxide‐semiconductor high electron mobility transistors (MOS‐HEMTs) on Si substrate. The impact of oxide/GaN interface traps with different energy levels on the switching behavior of the device was extensively examined by simulation and verified by measurements. The interface traps at 0.4 eV below the bottom of the conduction band (Eit = EC‐0.4 eV) of GaN buffer with a density of Dit= 6.5×1012 cm‐2 was identified responsible for the observed two‐stage turn‐on characteristic. The weak Fermi‐level pinning (WFLP) induced by the dynamic electron filling of interface traps may hamper the electron from accumulating in the Al2O3/GaN MOS‐channel and then manifests a premature turn‐on during the switching‐on process. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-03T06:40:22.824238-05:
      DOI: 10.1002/pssc.201510189
       
  • Temperature dependence of GaN MOS capacitor characteristics
    • Authors: Zhibo Guo; Ke Tang, T. Paul Chow
      Pages: 336 - 340
      Abstract: GaN MOS capacitors on both as‐grown and dry/wet‐etched GaN surfaces are characterized by C‐V and G‐ω measurements at elevated temperatures. The nature of GaN/SiO2 interface traps are determined in detail by extracting interface trap density, surface potential fluctuation, trap time constant and capture cross‐section. When temperature increases, trap time constant decreases so that more traps become active and contribute to observed higher interface trap density, especially for traps at deeper energy levels. The deeper trap levels activated at higher temperatures also induce corresponding temperature‐dependent surface potential fluctuation variations. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-01-27T02:40:10.047019-05:
      DOI: 10.1002/pssc.201510201
       
  • Investigation of breakdown properties in the carbon doped GaN by
           photoluminescence analysis
    • Authors: Deqiu Zhou; Yiqiang Ni, Zhiyuan He, Fan Yang, Yao Yao, Zhen Shen, Jian Zhong, Guilin Zhou, Yue Zheng, Liang He, Zhisheng Wu, Baijun Zhang, Yang Liu
      Pages: 345 - 349
      Abstract: The electrical and optical properties of the carbon doped GaN grown on Si substrate by metal‐organic chemical‐vapor deposition are investigated. Carbon impurity doping can improve the breakdown voltage effectively. However excess carbon in contrast depresses the breakdown voltage. This result is correlated with the carbon dopant behaviour in GaN which can be observed by analyzing the photoluminescence (PL) spectra. It is explained that the carbon impurity favours the formation of CN (carbon substitution of nitrogen) which acts as a deep level acceptor. The acceptor compensates the n‐type background impurities, which may resulting in suppressing the leakage current at high electric field, and leads to the improvement of the breakdown voltage. However, with excess carbon doping level, a significant amount of CGa (carbon substitution of gallium) form in GaN. The CGa, acting as the donor, compensates the CN and hence impairs the concentration of the deep level acceptor. In a result, the compensation of the n‐type background impurities by the deep level acceptor is curbed by the CGa‐CN self‐compensation effect, which leads to the decrease of the breakdown voltage. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-01-29T05:30:20.144927-05:
      DOI: 10.1002/pssc.201510176
       
  • Comparison of silicon, SiC and GaN power transistor technologies with
           breakdown voltage rating from 1.2 kV to 15 kV
    • Authors: Sauvik Chowdhury; Zhibo Guo, Xueqing Liu, T. Paul Chow
      Pages: 354 - 359
      Abstract: In recent years, different power transistors have been developed in silicon carbide (SiC) and gallium nitride (GaN) as replacements for silicon based IGBTs. This paper presents a simulation comparison of the static and dynamic performance of silicon IGBTs with different SiC and GaN based lateral and vertical power transistors (HEMT, MOSFET and IGBT) with breakdown voltage ratings between 1.2 kV to 15 kV. The strengths and weaknesses of different technologies which make them suitable at different voltage levels have been discussed. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-01-27T02:40:09.141018-05:
      DOI: 10.1002/pssc.201510200
       
  • On‐chip addressable Schottky‐on‐heterojunction
           
    • Authors: Xi Tang; Baikui Li, Yunyou Lu, Kevin J. Chen
      Pages: 365 - 368
      Abstract: In this work, the Schottky‐on‐heterojunction light‐emitting diodes (SoH‐LED) are monolithically integrated with the AlGaN/GaN high‐electron‐mobility transistors (HEMT) on an AlGaN/GaN‐on‐Si platform commonly used for GaN lateral electronic devices. The on‐chip electro‐optic modulation is realized in a single device fabricated using HEMT‐compatible process. Also, SoH‐LED arrays are fabricated to demonstrate the on‐chip addressable functionality with each SoH‐LED pixel in the array individually controlled by the integrated HEMT. High‐resolution micro‐scale SoH‐LED seven‐segment displays are demonstrated to show the potential of using SoH‐LEDs as a robust alternative for micro flat‐panel displays. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-02-17T03:40:03.490809-05:
      DOI: 10.1002/pssc.201510169
       
  • Modulation of the domain mode in GaN‐based planar Gunn diode for
           terahertz applications
    • Pages: 382 - 385
      Abstract: This paper reports the modulation of the domain mode in the 2DEG channel of GaN HEMT‐like Gunn diodes by adjustment the electron concentration of the 2DEG near the cathode side. The enhancement of the electron concentration near the cathode side promotes the fast formation of the dipole domain layer and greatly reduces the dead zone length, which increases the RF output power. The employment of the recess layer near the cathode reduces the electron concentration of the 2DEG beneath it, which acts as a notch‐doped layer as in the bulk vertical diode. The reduction of the electron concentration of the 2DEG near the cathode promotes the formation of dual‐domain in one oscillation circle, which aims to enhance harmonic components of Gunn oscillation so as to minimize the use of frequency multipliers for SMMW and THz operation. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
      PubDate: 2016-01-29T05:30:16.036956-05:
      DOI: 10.1002/pssc.201510158
       
 
 
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