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Journal Cover Semiconductors and Semimetals
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   ISSN (Print) 0080-8784
   Published by Elsevier Homepage  [3034 journals]
  • Series Page
    • Abstract: Publication date: 2017
      Source:Semiconductors and Semimetals, Volume 97

      PubDate: 2017-06-20T07:33:08Z
  • Rare-Earth-Containing Materials for Photoelectrochemical Water Splitting
    • Authors: Jennifer Leduc; Yakup Aida Raauf Thomas Fischer Sanjay Mathur
      Abstract: Publication date: Available online 9 June 2017
      Source:Semiconductors and Semimetals
      Author(s): Jennifer Leduc, Yakup Gönüllü, Aida Raauf, Thomas Fischer, Sanjay Mathur
      Rare earth elements have become increasingly important in catalytic and energy production processes largely due to their optoelectronic properties emerging from their unique electronic structure and the influence of 4f electrons. Lanthanide-containing materials additionally offer the opportunity to tune light absorption in infrared region and convert the long wavelength excitation energy into shorter wavelength output through an upconversion process, which effectively improves the overall light harvesting and photon management in the materials. In this chapter, we review the potential of rare-earth-doped materials, rare earth-based oxide–oxide composites, and ternary oxide materials in the fields of photoelectrochemical and photocatalytic water splitting. Following a brief account of the physical principles governing the energy absorption and conversion in rare earth materials, comprehensive analysis of the photocatalytic activity of lanthanide-based materials and their structural and electronic modifications is provided. Finally, the status and perspectives of rare earth materials in photoelectrochemical tandem cells are discussed that underline the significance of this material class in addressing the challenges of clean and sustainable energy.

      PubDate: 2017-06-10T16:16:53Z
  • Effective Charge Carrier Utilization in Visible-Light-Driven CO2
    • Authors: Xiaoxia Chang; Tuo Wang; Jinlong Gong
      Abstract: Publication date: Available online 25 May 2017
      Source:Semiconductors and Semimetals
      Author(s): Xiaoxia Chang, Tuo Wang, Jinlong Gong
      Due to the excessive utilization of fossil fuels and the accompanied large CO2 emission amounts, global warming and energy crisis have been recognized as two main challenges of the 21st century. The conversion of CO2 into fuels such as methane or methanol using photocatalysts and solar energy is believed to be one of the best methods to address these two problems. However, the activation of CO2 linear molecule, the low solar energy conversion efficiency and the diversity of reduction products are still great challenges. It is of significant importance to develop the high-performance photocatalysts, effectively utilize the charge carriers, and efficiently manage the surface reactions to maximize the activity and selectivity for photoconversion of CO2 and H2O to solar fuels. This chapter describes the fundamental understanding of CO2 photoreduction on the surface of heterogeneous catalysts as well as recent advances in the CO2 reduction on visible-light photocatalysts. The challenges and perspectives of CO2 photoreduction for future development are also presented.

      PubDate: 2017-05-26T04:48:57Z
      DOI: 10.1016/bs.semsem.2017.04.004
  • Black Titanium Dioxide for Photocatalysis
    • Authors: Yan Liu; Xiaobo Chen
      Abstract: Publication date: Available online 23 May 2017
      Source:Semiconductors and Semimetals
      Author(s): Yan Liu, Xiaobo Chen
      Photocatalysis has been regarded as one of the best solutions to using the sunlight to produce hydrogen (H2) from water and to remove organic pollutants from the environment, and titanium dioxide (TiO2) nanomaterials have been treated as the primary photocatalyst for this purpose. However, the large band gap of TiO2 has largely limited its activity to the UV region of the solar spectrum. The discovery of black TiO2 in 2011 has triggered world-wide research interests in this material. In this chapter, the recent progress of the synthesis, properties, and photocatalysis of the black TiO2 nanomaterials are briefly summarized.

      PubDate: 2017-05-26T04:48:57Z
      DOI: 10.1016/bs.semsem.2017.04.001
  • Facet Control of Photocatalysts for Water Splitting
    • Authors: Jian Pan; Gang Liu
      Abstract: Publication date: Available online 23 May 2017
      Source:Semiconductors and Semimetals
      Author(s): Jian Pan, Gang Liu
      Tailored photocatalysts with well-defined facets have been achieved in recent years, from the synthetic study of faceted crystals to the intrinsic property investigation of exposed surface, and to the overall performance in different applications. So far, the faceted crystals have shown encouraging improvement in the field of environment and energy applications. Among them, photocatalytic water splitting is a significant process to convert solar energy into chemical energy by dissociating water into hydrogen and oxygen. In this chapter, we mainly focus on the facet controlling of photocatalysts for water-splitting processes. For water reduction, the facet engineering of anatase, rutile, and brookite TiO2 is introduced, as well as some other faceted photocatalysts, Cu2O and CdS; For water oxidation, three most popular photocatalysts, Ag3PO4, BiVO4, and WO3, and their developments in facet control are reviewed, and for overall water splitting, perovskite-type oxides, NaTaO3, and SrTiO3 are briefly summarized.

      PubDate: 2017-05-26T04:48:57Z
      DOI: 10.1016/bs.semsem.2017.04.003
  • Nanostructured Photoelectrodes via Template-Assisted Fabrication
    • Authors: Rowena Yew; Siva Krishna Karuturi; Hark Hoe Tan; Chennupati Jagadish
      Abstract: Publication date: Available online 16 May 2017
      Source:Semiconductors and Semimetals
      Author(s): Rowena Yew, Siva Krishna Karuturi, Hark Hoe Tan, Chennupati Jagadish
      Nanostructured materials are crucial to the light harvesting and power conversion efficiency of solar energy conversion systems. The template-assisted fabrication method offers a versatile route to produce nanostructured materials of controlled morphology and optoelectronic properties. Toward this, self-assembled opal colloidal crystals and nanoporous anodic aluminum oxide have been used as templates to produce nanostructures of a wide range of materials with different dimensionalities and enhanced photocatalytic properties. This chapter introduces various approaches developed for producing the templates and methods of infiltrating them with the desired photoactive materials. This chapter also critically assesses the advantages and limitations of the proposed methods, and summarizes the beneficial outcomes realized using nanostructures developed through the template-assisted route for photocatalysis.

      PubDate: 2017-05-21T02:06:45Z
      DOI: 10.1016/bs.semsem.2017.04.002
  • III-Nitride Semiconductor Photoelectrodes
    • Authors: Katsushi Fujii
      Abstract: Publication date: Available online 15 May 2017
      Source:Semiconductors and Semimetals
      Author(s): Katsushi Fujii
      III-Nitrides can cover a wide range of light absorption from infrared (IR) to ultraviolet (UV) and show good crystal qualities, which can be used for light-emitting devices. This means that III-nitrides are good materials to evaluate the photoelectrochemical mechanisms. Here, the photoelectrochemical properties, especially for the band edge energies and anodic photocorrosion mechanisms, are discussed based on the semiconductor electrochemistry. The properties of electrocatalyst on III-nitride surface, CO2 reduction at the counter cathode electrode with using III-nitride photoanode, and the photoelectrochemical properties of In x Ga1− x N, p-type III-nitrides, and nanoporous GaN are also discussed here.

      PubDate: 2017-05-15T23:59:00Z
      DOI: 10.1016/bs.semsem.2017.03.003
  • III–V Semiconductor Photoelectrodes
    • Authors: Georges Siddiqi; Zhenhua Pan; Shu Hu
      Abstract: Publication date: Available online 26 April 2017
      Source:Semiconductors and Semimetals
      Author(s): Georges Siddiqi, Zhenhua Pan, Shu Hu
      In the past decades, great efforts have been made to develop efficient solar-to-fuel conversion devices using III–V semiconductors. In this chapter, a brief history of III–V photoelectrodes for photochemistry and their synthesis methods are firstly reviewed. Then, an important category of solar-energy-conversion devices, photoelectrochemical solar cells, constructed by III–V photoelectrodes in contact with redox couples is discussed. The discussion also includes up-to-date basic understanding of the interfacial photoelectrochemistry between semiconductors, redox, and catalysts with liquid electrolytes. Finally, fuel-forming photoelectrodes for hydrogen evolution, water oxidation, overall water splitting, and CO2 reduction are summarized, with emphasis on the recently developed protective coating strategies.

      PubDate: 2017-04-30T17:25:21Z
      DOI: 10.1016/bs.semsem.2017.03.002
  • Light-Induced Water Splitting Using Layered Metal Oxides and Nanosheets
    • Authors: Takayoshi Oshima; Miharu Eguchi; Kazuhiko Maeda
      Abstract: Publication date: Available online 17 April 2017
      Source:Semiconductors and Semimetals
      Author(s): Takayoshi Oshima, Miharu Eguchi, Kazuhiko Maeda
      Layered metal oxides and their nanosheets are interesting materials as photocatalysts for water splitting. In particular, semiconductor nanosheets are attractive building blocks for synthesizing a photocatalytic material because of their high surface area and the wide variety of compositions available. The anisotropic feature of nanosheets, which have a thickness of ~1nm and lateral dimensions ranging from several hundred nanometers to a few micrometer, is advantageous for heterogeneous photocatalysts, as the diffusion length of photogenerated electrons and holes to the surface is shortened, resulting in higher activity. In this chapter, recent progress of layered metal oxide and their nanosheets for application in photocatalytic water splitting made by our group is described.

      PubDate: 2017-04-23T14:51:34Z
      DOI: 10.1016/bs.semsem.2017.02.001
  • Photophysics and Photochemistry at the Semiconductor/Electrolyte Interface
           for Solar Water Splitting
    • Authors: Xiaogang Yang; Dunwei Wang
      Abstract: Publication date: Available online 5 April 2017
      Source:Semiconductors and Semimetals
      Author(s): Xiaogang Yang, Dunwei Wang
      Since its initial demonstration, semiconductor-based solar water splitting has seen an unprecedented continuation of efforts for almost 50 years. Yet, the overall performance of this approach remains impractically low. An important reason for the slow progress is the lack of understanding. The limited knowledge obtained on a few model systems has been found difficult to transfer or generalize, creating one of the most daunting challenges faced by the scientific community. It has been recognized that solutions to this challenge will likely rely on combined knowledge of solid-state physics, electrochemistry, and catalysis. To illustrate the issues faced by semiconductor-based solar water splitting, and to contribute to the eventual goal of realizing the approach with economically competitive performance, we put together this chapter. We focus on the semiconductor/water interface and discuss the fundamental processes and concepts important to the understanding of the complex system. Our primary goal is to provide new background information that can facilitate the formation of new insight into the phenomena. For this purpose, special emphasis is given to the interface behaviors.

      PubDate: 2017-04-08T20:50:43Z
      DOI: 10.1016/bs.semsem.2017.03.001
  • Artificial Photosynthesis on III-Nitride Nanowire Arrays
    • Authors: Sheng Chu; Xianghua Kong; Srinivas Vanka; Hong Guo; Zetian Mi
      Abstract: Publication date: Available online 29 March 2017
      Source:Semiconductors and Semimetals
      Author(s): Sheng Chu, Xianghua Kong, Srinivas Vanka, Hong Guo, Zetian Mi
      Artificial photosynthesis, which mimics the nature photosynthesis process to store solar energy into energy-rich chemical fuels, is considered as a promising method for providing a carbon-neutral, renewable, and scalable source of energy. Despite a variety of materials and designs have been explored over the past four decades, a viable artificial photosynthetic system for large-scale practical application has yet to be developed. Recently, III-nitride materials have emerged as a new generation of photocatalysts to break the effciency bottleneck in the field of artificial photosynthesis. In this chapter, we review the state-of-the-art research activities made on III-nitride nanowire arrays for artificial photosynthesis, with a focus on the design and development of efficient III-nitride materials (i.e., GaN and InGaN) for water splitting and CO2 reduction via photocatalytic and photoelectrochemical approaches.

      PubDate: 2017-04-01T19:48:26Z
      DOI: 10.1016/bs.semsem.2017.02.004
  • Nanostructured Semiconductors for Bifunctional Photocatalytic and
           Photoelectrochemical Energy Conversion
    • Authors: Songcan Wang; Jung-Ho Yun; Lianzhou Wang
      Abstract: Publication date: Available online 28 March 2017
      Source:Semiconductors and Semimetals
      Author(s): Songcan Wang, Jung-Ho Yun, Lianzhou Wang
      Bifunctional photocatalytic (PC) and photoelectrochemical (PEC) systems have attracted increasing attention due to their advantages of making good use of both photoexcited electrons and holes for simultaneous solar fuel production, organic pollutant degradation, value-added chemical, or electricity generation. Compared to conventional PC and PEC systems, only limited reports have systematically studied this new emerging research field. This chapter aims to provide readers the underlying fundamentals including the working mechanisms and configurations of bifunctional PC/PEC systems. A few types of bifunctional systems are discussed and recent development of nanostructured semiconductors for bifunctional PC/PEC systems is also concisely summarized. The challenges and future developments are also discussed at the end of the chapter.

      PubDate: 2017-04-01T19:48:26Z
      DOI: 10.1016/bs.semsem.2017.02.003
  • Charge Carrier Dynamics in Metal Oxide Photoelectrodes for Water Oxidation
    • Authors: Andreas Kafizas; Robert Godin; James R. Durrant
      Abstract: Publication date: Available online 24 March 2017
      Source:Semiconductors and Semimetals
      Author(s): Andreas Kafizas, Robert Godin, James R. Durrant
      Since the first demonstration by Fujishima and Honda of photoelectrochemical water splitting, this route to renewable hydrogen fuel has been pursued with great endeavor. The oxidation of water has been identified as the kinetic “bottleneck” limiting the overall reaction efficiency, thus there is a pressing need to develop more active photocatalysts that can drive this reaction. Some of the most promising materials that can oxidize water are metal oxide semiconductors. The most popular metal oxide photoanodes for water oxidation are TiO2, α-Fe2O3, BiVO4, and WO3, but even state-of-the-art examples show photocatalytic currents far shy of their theoretical maximum. Numerous strategies have been developed to improve their activity, which include nanostructuring, the use of surface cocatalysts, pacifying surface states, and forming heterojunction architectures. This review focuses on the use of TiO2, α-Fe2O3, BiVO4, and WO3 as photoanodes for water oxidation and studies that probe charge carrier dynamics. Emphasis is placed on evaluation of electrodes under operating conditions. During this review, we will discuss each metal oxide in turn and use these studies of charge carrier dynamics to build an inclusive and complimentary picture of the processes that occur during water oxidation. There will be a general view on how changes in material structure impact charge carrier dynamics and the kinetics of water oxidation.

      PubDate: 2017-03-25T18:20:39Z
      DOI: 10.1016/bs.semsem.2017.02.002
  • Series Page
    • Abstract: Publication date: 2017
      Source:Semiconductors and Semimetals, Volume 96

      PubDate: 2017-01-09T18:10:39Z
  • Contents of Volumes in this Series
    • Abstract: Publication date: 2017
      Source:Semiconductors and Semimetals, Volume 96

      PubDate: 2017-01-09T18:10:39Z
  • Materials Challenges of AlGaN-Based UV Optoelectronic Devices
    • Authors: M.H. Crawford
      Abstract: Publication date: Available online 27 December 2016
      Source:Semiconductors and Semimetals
      Author(s): M.H. Crawford
      Over the past 15 years, tremendous progress has been made in AlGaN-based optoelectronic devices, including light-emitting diodes (LEDs) and laser diodes (LDs) in the deep UV (DUV) region of the spectrum. However, performance levels are still lagging those of InGaN light emitters in the visible region due to outstanding materials challenges of the wider band gap AlGaN alloys. In this review, we focus on two of the most significant materials roadblocks to higher-performing AlGaN devices: doping and substrates. For each topic, we present the state of the art as well as exploratory concepts for enabling future device advances. On the topic of p-type doping, we describe the concomitant challenges of large acceptor activation energy, dopant solubility, and compensating defects and describe growth optimization approaches to mitigate those issues. We further present polarization engineering approaches to enhance p-type doping, including Mg-doped superlattices, distributed polarization doping, and tunnel-junction-enabled LEDs. Limitations to n-type doping for high-Al-composition AlGaN alloys are also reviewed along with insights into the origins these doping challenges. On the topic of substrates, we report the challenges of heteroepitaxy on lattice-mismatched substrates, describe the impact of high dislocation densities on AlGaN emitters, and overview strategies for dislocation reduction. State-of-the-art UV LD performance, enabled by these defect reduction strategies, is also presented. Limitations due to electrically insulating substrates are described as well as promising approaches to achieving vertical-injection UV light emitters. Overall, common themes of employing material and device structures at the micro/nanoscale and leveraging the polarization properties of nitride heterostructures reveal approaches for realizing next-generation UV light emitters.

      PubDate: 2016-12-30T12:51:33Z
      DOI: 10.1016/bs.semsem.2016.11.001
  • Growth of High-Quality AlN on Sapphire and Development of AlGaN-Based
           Deep-Ultraviolet Light-Emitting Diodes
    • Authors: Hirayama
      Abstract: Publication date: Available online 23 December 2016
      Source:Semiconductors and Semimetals
      Author(s): H. Hirayama
      222–351nm AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs) are demonstrated, which has been achieved by the development of crystal growth techniques for wide-bandgap AlN and AlGaN. Significant increases in internal quantum efficiency have been achieved for AlGaN quantum-well emissions by introducing low-threading dislocation density AlN grown by an NH3 pulsed-flow multilayer growth method. Electron injection efficiency of the DUV LED was significantly increased by introducing multiquantum barrier. Light extraction efficiency was also improved by using a transparent p-AlGaN contact layer. The maximum external quantum efficiency was increased up to 7% for a 279-nm DUV LED.

      PubDate: 2016-12-30T12:51:33Z
  • Dynamic Atomic Layer Epitaxy of InN on/in GaN and Its Application for
           Fabricating Ordered Alloys in Whole III-N System
    • Authors: K. Kusakabe; A. Yoshikawa
      Abstract: Publication date: Available online 30 November 2016
      Source:Semiconductors and Semimetals
      Author(s): K. Kusakabe, A. Yoshikawa
      A unique epitaxial process, dynamic atomic layer epitaxy (D-ALEp), has been proposed and developed to fabricate coherent monolayer-InN on/in GaN-matrix nanostructures. The D-ALEp utilizes self-limiting and self-ordering surface processes but differs from typical atomic layer epitaxy, because the growth front in D-ALEp dynamically changes stoichiometry or metal coverage through adsorption/desorption of adatoms at a high-temperature regime. The growth front is precisely traced by in situ spectroscopic ellipsometry monitoring, where atomic scale surface behavior is easily/accurately understood by our smart style of an imaginary part of pseudodielectric function normalized by an adlayer thickness (Δ〈ɛ 2〉), instead of complicated spectral analysis. In this chapter, the authors briefly introduce the D-ALEp and also our prime objective to establish ordered alloys in a whole III-nitride system. Subsequently, the authors discuss growth kinetics of monolayer-InN on/in GaN-matrix by the D-ALEp which has been developed in molecular beam epitaxy (MBE) at the beginning to overcome highly mismatched problems in an InN/GaN system, and then investigated in metalorganic vapor phase epitaxy (MOVPE) as well. Finally, the authors represent an extension of the D-ALEp toward fabrication of III-N ordered alloys. The authors have demonstrated InN/GaN ordered alloys grown by MBE and (InN/GaN)-layer/pn-GaN solar cells grown by MOVPE. The authors further discuss a future prospect of AlN/GaN and AlN/InN ordered alloys for potential application to high electron mobility transistors (HEMTs).

      PubDate: 2016-12-01T05:08:30Z
      DOI: 10.1016/bs.semsem.2016.10.001
  • III-N Wide Bandgap Deep-Ultraviolet Lasers and Photodetectors
    • Authors: T. Detchprohm; X. Li; S.-C. Shen; P.D. Yoder; R.D. Dupuis
      Abstract: Publication date: Available online 4 November 2016
      Source:Semiconductors and Semimetals
      Author(s): T. Detchprohm, X. Li, S.-C. Shen, P.D. Yoder, R.D. Dupuis
      The III-N wide-bandgap alloys in the AlInGaN system have many important and unique electrical and optical properties which have been exploited to develop deep-ultraviolet (DUV) optical devices operating at wavelengths <300nm, including light-emitting diodes, optically pumped lasers, and photodetectors. In this chapter, we review some aspects of the development and current state of the art of these DUV materials and devices. We describe the growth of III-N materials in the UV region by metalorganic chemical vapor deposition as well as the properties of epitaxial layers and heterostructure devices. In addition, we discuss the simulation and design of DUV laser diodes, the processing of III-N optical devices, and the description of the current state of the art of DUV lasers and photodetectors.

      PubDate: 2016-11-09T20:08:03Z
      DOI: 10.1016/bs.semsem.2016.09.001
  • Nitride Semiconductor Nanorod Heterostructures for Full-Color and
           White-Light Applications
    • Authors: S. Gwo; Y.J. Lu; H.W. Lin; C.T. Kuo; C.L. Wu; M.Y. Lu; L.J. Chen
      Abstract: Publication date: Available online 31 October 2016
      Source:Semiconductors and Semimetals
      Author(s): S. Gwo, Y.J. Lu, H.W. Lin, C.T. Kuo, C.L. Wu, M.Y. Lu, L.J. Chen
      Development of full-color and white light-emitting diodes (LEDs) and laser diodes (LDs) is tremendously important for energy-efficient lighting and advanced display applications. At present, the InGaN/GaN semiconductor heterostructure system is considered as the most promising device candidate for these applications because the direct band gap of In x Ga1− x N spans from the near-infrared (NIR) to the near-UV, including the complete visible spectrum. However, there are severe issues related to structural imperfection and polarization effects in high-In-content InGaN/GaN semiconductor heterostructures, resulting in low emission efficiency in the long-wavelength spectral region (beyond blue). To overcome the formidable material challenges in InGaN/GaN semiconductor heterostructures, many studies reported recently have suggested a promising solution based on full-color and white solid-sate emitters using one-dimensional (1D) nitride semiconductor nanostructures (nanorods, nanowires, nanocolumns, nanopillars, nanotubes, etc.). Especially, vertically self-aligned GaN nanorod arrays have been applied as strain-free or strain-reduced growth templates for heteroepitaxial growth of InGaN/GaN nanorod heterostructures emitting in the full visible spectrum. Moreover, 1D nitride semiconductor nanorod heterostructures can be grown by plasma-assisted molecular beam epitaxy and metal-organic vapor phase epitaxy with well-defined axial/radial geometries and abruptly modulated compositions to achieve unique device functionalities. In this chapter, we give a detailed discussion about nitride semiconductor nanorod heterostructures, including polarization effects, nanorod growth and polarity control, doping and surface properties, nanorod heterojunction band alignments, axial nanorod heterostructures for full-color and tunable white LEDs, as well as green and full-color core–shell nanorod plasmonic nanolasers. Some future perspectives will also be given for both fundamental studies and new device applications of nitride semiconductor nanorod heterostructures.

      PubDate: 2016-11-02T14:43:53Z
      DOI: 10.1016/bs.semsem.2016.09.002
  • Growth and Structural Characterization of Self-Nucleated III-Nitride
    • Authors: T. Auzelle; B. Daudin
      Abstract: Publication date: Available online 24 September 2016
      Source:Semiconductors and Semimetals
      Author(s): T. Auzelle, B. Daudin
      We review the self-nucleation process of GaN nanowires grown by plasma-assisted molecular beam epitaxy. The role of GaN/Si (111) and of AlN/Si (111) interface chemistry is shown to be determinant and is analyzed in details. The crucial issue of GaN crystalline polarity is shown to depend on both interface chemistry and GaN facet surface energy. The structural properties of self-nucleated GaN NWs are next discussed, with a peculiar focus on stacking faults and inversion domains.

      PubDate: 2016-09-28T18:34:23Z
      DOI: 10.1016/bs.semsem.2016.08.004
  • Development of Deep UV LEDs and Current Problems in Material and Device
    • Authors: M. Shatalov; R. Jain; T. Saxena; A. Dobrinsky; M. Shur
      Abstract: Publication date: Available online 10 September 2016
      Source:Semiconductors and Semimetals
      Author(s): M. Shatalov, R. Jain, T. Saxena, A. Dobrinsky, M. Shur
      We review progress in development of deep ultraviolet light-emitting diodes and discuss key factors currently affecting device performance. Heteroepitaxial growth of AlN and AlGaN by high-temperature epitaxy has resulted in significant improvement of LED efficiency through reduction of density of nonradiative defects. Importance of alloy composition fluctuations is discussed based on results of time-resolved temperature-dependent photoluminescence and light-induced grating measurements of Al0.6Ga0.4N layers with different density of dislocations. Improvement of LED performance achieved by suppression of the nonradiative recombination in epitaxial structures with dislocation density reduced to below 5×108 cm−2, transparent LED structure design, and optimized UV-reflective contacts. Aspects of the LED chip design are discussed for further improvements of light extraction and LED output power. Research is now under way to use these devices for numerous applications including water and air purification, sterilization, biological threat identification, applications in medicine, biology, industrial processes, defense, and homeland security.

      PubDate: 2016-09-19T05:29:48Z
      DOI: 10.1016/bs.semsem.2016.08.002
  • InN Nanowires: Epitaxial Growth, Characterization, and Device Applications
    • Authors: Zhao
      Abstract: Publication date: Available online 6 September 2016
      Source:Semiconductors and Semimetals
      Author(s): S. Zhao, Z. Mi
      In this chapter, we review the recent progress made on the growth, characterization, and device applications of InN nanowires. Early research on InN nanowires is limited by their n-type degenerate characteristics, wherein the Fermi level is located deep in the conduction band, with the presence of high-density surface electrons. Recently, with the improved molecular beam epitaxy growth process, intrinsic and p-type InN nanowires have been realized, which are free of surface electron accumulation and Fermi-level pinning, providing great promise for a broad range of devices and applications.

      PubDate: 2016-09-10T00:56:51Z
  • Selective Area Growth of InGaN/GaN Nanocolumnar Heterostructures by
           Plasma-Assisted Molecular Beam Epitaxy
    • Authors: S. Albert; A.M. Bengoechea-Encabo; M.Á. Sánchez-García; E. Calleja
      Abstract: Publication date: Available online 3 September 2016
      Source:Semiconductors and Semimetals
      Author(s): S. Albert, A.M. Bengoechea-Encabo, M.Á. Sánchez-García, E. Calleja
      The aim of this work is to gain insight into the selective area growth (SAG) of InGaN nanostructures by plasma-assisted molecular beam epitaxy, focusing on their potential as building blocks for next-generation LEDs. Several nanocolumn (NC)-based approaches such as standard axial InGaN/GaN structures and InGaN/GaN core–shell structures are discussed. The first section reports on the growth and characterization of ordered InGaN NCs as well as light-emitting diodes grown on c-plane GaN/sapphire templates. In particular, the growth mechanism of green-emitting InGaN/GaN NCs is discussed. In order to enable white light emission the stacking of red, green, and blue emitting segments is used to achieve the monolithic integration of these structures in one single InGaN NC allowing for the fabrication of ordered broad spectrum emitters. As alternative to axial InGaN/GaN nanostructures, the next section reports on the growth and characterization of InGaN/GaN core–shell structures with emission at around 3.0eV. Furthermore, the successful fabrication of a core–shell pin diode structure is demonstrated. Finally, the SAG of In(Ga)N/GaN NCs on Si(111) substrates is presented. Ordered In(Ga)N/GaN NCs emitting from ultraviolet (3.2eV) to infrared (0.78eV) were grown on top of GaN-buffered Si substrates.

      PubDate: 2016-09-05T02:02:32Z
      DOI: 10.1016/bs.semsem.2016.08.003
  • III-Nitride Electrically Pumped Visible and Near-Infrared Nanowire Lasers
           on (001) Silicon
    • Authors: P. Bhattacharya; A. Hazari; S. Jahangir; W. Guo; T. Frost
      Abstract: Publication date: Available online 25 August 2016
      Source:Semiconductors and Semimetals
      Author(s): P. Bhattacharya, A. Hazari, S. Jahangir, W. Guo, T. Frost
      Ga(Al,In)N nanowires can be grown catalyst-free on silicon and other substrates. The diameter of individual nanowires in an array and the array density can be varied over wide ranges. Single or multiple InGaN disks can be inserted in Ga(Al)N nanowires and the alloy composition in the disk can be varied to tune the luminescence from visible to near infrared. The nanowires have other desirable properties such as very low density of extended defects and minimal strain. They can also be selectively doped n- and p-type, thereby enabling the formation of junction diodes as with planar materials. With adequate passivation the internal quantum efficiency of GaN nanowires and the InGaN disks, which behave as quantum dots, is higher than 50%. We have exploited these favorable attributes to design, epitaxially grow and characterize the first edge-emitting electrically pumped GaN/In(Ga)N disk-in-nanowire lasers with the peak of the coherent emission varying from 533nm (green) to 1.3μm. It may be noted that light sources with emission at wavelengths larger than 590nm cannot be realized with InGaN/GaN quantum wells (QWs). The characteristics of the nanowire heterostructures and the steady-state and small-signal modulation characteristics of the lasers are described. The threshold current, characteristic temperature T 0, differential gain, and modulation bandwidth of the nanowire lasers are comparable to state-of-the-art QW and quantum dot lasers.

      PubDate: 2016-08-26T14:45:29Z
      DOI: 10.1016/bs.semsem.2016.07.002
  • Exploring the Next Phase in Gallium Nitride Photonics: Cubic Phase Light
           Emitters Heterointegrated on Silicon
    • Authors: C. Bayram; R. Liu
      Abstract: Publication date: Available online 29 July 2016
      Source:Semiconductors and Semimetals
      Author(s): C. Bayram, R. Liu
      Gallium nitride (GaN) materials are the backbone of emerging solid-state lighting. To date, GaN research has been primarily focused on hexagonal phase devices due to the natural crystallization. This approach limits the output power and efficiency of light-emitting diodes (LEDs), particularly in the green spectrum. However, GaN can also be engineered to be in cubic phase. Cubic GaN has a lower bandgap (~200meV) than hexagonal GaN that enables green LEDs much easily. Besides, cubic GaN has more isotropic properties (smaller effective masses, higher carrier mobility, higher doping efficiency, and higher optical gain than hexagonal GaN) and cleavage planes. Due to phase instability, however, cubic phase materials and devices have remained mostly unexplored. Here we review a new method of cubic phase GaN generation: hexagonal-to-cubic phase transition, based on novel nanopatterning. We report a new crystallographic modeling of this hexagonal-to-cubic phase transition and systematically study the effects of nanopatterning on the GaN phase transition via transmission electron microscopy, temperature-dependent cathodoluminescence, and electron backscatter diffraction experiments. In summary, silicon-integrated cubic phase GaN light emitters offer a unique opportunity for exploration in next-generation photonics.

      PubDate: 2016-08-06T05:20:06Z
      DOI: 10.1016/bs.semsem.2016.07.001
  • Al(Ga)N Nanowire Deep Ultraviolet Optoelectronics
    • Authors: Zhao
      Abstract: Publication date: Available online 9 July 2016
      Source:Semiconductors and Semimetals
      Author(s): S. Zhao, Z. Mi
      In this chapter, we review the recent progress made on the growth and characterization of Al(Ga)N nanowires and related optoelectronic devices, with a focus on Al-rich Al(Ga)N nanowires and their applications for deep ultraviolet (UV) light-emitting diodes (LEDs) and lasers. The achievement of nearly defect-free Al(Ga)N nanowires by molecular beam epitaxy, the realization of efficient p-type conduction in AlN and Al-rich ternary AlGaN nanowires, and the demonstration of high efficiency Al(Ga)N nanowire LEDs are described. Moreover, the presence of quantum-confined nanostructures in ternary AlGaN nanowires and the first demonstrations of electrically injected semiconductor lasers in the UV-B and UV-C bands are also presented.

      PubDate: 2016-08-06T05:20:06Z
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