Sample records for gian gan day

  1. A CERN physicist receives the Gian Carlo Wick Medal


    T.D. Lee, Chairman of the Gian Carlo Wick Medal selection committee, André Martin, the 2007 recipient, and Antonino Zichichi, President of the World Federation of Scientists (WFS)(Copyright : WFS) The 2007 Gian Carlo Wick Gold Medal was presented to the CERN theoretical physicist André Martin in Erice (Italy) on 20 August. The prize is awarded each year by the WFS (World Federation of Scientists), whose president is Professor Antonino Zichichi, to a theoretical physicist for his outstanding contributions to particle physics. The selection committee is composed of eminent physicists and is chaired by the Nobel Physics Prize Laureate, T.D. Lee. André Martin was awarded the Medal in recognition of his work on the total cross-section for interactions between two particles and his contributions to the understanding of heavy quark-antiquark (or quarkonium) systems. In 1965, André Martin established a theoretical basis for the so-call...

  2. Gian Carlo Ferretti - Giulia Iannuzzi, Storie di uomini e libri

    Laura Pennacchietti


    Full Text Available Anyone who is familiar with the history of Italian publishing will have come across the name of Gian Carlo Ferretti. He is one of the leading critics and scholars in the field and has engaged in extensive research since the sixties, writing an impressive number of volumes and contributions – among them, the seminal text Storia dell’editoria letteraria in Italia, 1945-2003, published by Einaudi in 2004. Storie di uomini e libri, co-authored with Giulia Iannuzzi, relates to the line of research opened and developed by Ferretti throughout his life on the relation between literature, market, and cultural production. The premise of this volume, and of Ferretti’s entire work, is that literature, culture, and publishing industry are inextricably linked...

  3. GIAnT - Generic InSAR Analysis Toolbox

    Agram, P.; Jolivet, R.; Riel, B. V.; Simons, M.; Doin, M.; Lasserre, C.; Hetland, E. A.


    We present a computing framework for studying the spatio-temporal evolution of ground deformation from interferometric synthetic aperture radar (InSAR) data. Several open-source tools including Repeat Orbit Interferometry PACkage (ROI-PAC) and InSAR Scientific Computing Environment (ISCE) from NASA-JPL, and Delft Object-oriented Repeat Interferometric Software (DORIS), have enabled scientists to generate individual interferograms from raw radar data with relative ease. Numerous computational techniques and algorithms that reduce phase information from multiple interferograms to a deformation time-series have been developed and verified over the past decade. However, the sharing and direct comparison of products from multiple processing approaches has been hindered by - 1) absence of simple standards for sharing of estimated time-series products, 2) use of proprietary software tools with license restrictions and 3) the closed source nature of the exact implementation of many of these algorithms. We have developed this computing framework to address all of the above issues. We attempt to take the first steps towards creating a community software repository for InSAR time-series analysis. To date, we have implemented the short baseline subset algorithm (SBAS), NSBAS and multi-scale interferometric time-series (MInTS) in this framework and the associated source code is included in the GIAnT distribution. A number of the associated routines have been optimized for performance and scalability with large data sets. Some of the new features in our processing framework are - 1) the use of daily solutions from continuous GPS stations to correct for orbit errors, 2) the use of meteorological data sets to estimate the tropospheric delay screen and 3) a data-driven bootstrapping approach to estimate the uncertainties associated with estimated time-series products. We are currently working on incorporating tidal load corrections for individual interferograms and propagation of

  4. Text and Image. Fresco of Iphigenia from Gian Battista Tiepolo. Villa Valmarana near Vicenza

    Anna Chiarloni


    Full Text Available This essay examines the representation of the sacrifice of Iphigenia in the fresco by Gian Battista Tiepolo, located in Villa Valmarana near Vicenza. It explores the origins of the myth, beginning with the tragedy of Aeschylus, and continues to explore interpretations in the Latin literature until the Baroque period. The essay focuses especially on the patriarchal figure of Agamemnon, and the meaning of his hidden face.

  5. The Star and the Whole Gian-Carlo Rota on Mathematics and Phenomenology

    Palombi, Fabrizio


    The Star and the Whole: Gian-Carlo Rota on Mathematics and Phenomenology, authored by Fabrizio Palombi, is the first book to study Rota's philosophical reflection. Rota (1932--1999) was a leading figure in contemporary mathematics and an outstanding philosopher, inspired by phenomenology, who made fundamental contributions to combinatorial analysis, and trained several generations of mathematicians in his long career at the Massachusetts Institute of Technology (MIT) and the Los Alamos National Laboratory. The first chapter of the book reconstructs Rota's cultural biography and examines his ph

  6. Grassroots Innovations to Techno-Entrepreneurship through GIAN – Technology Business Incubator in India: A Case Study of Nature Technocrats

    Hemantkumar P. Bulsara


    Full Text Available Entrepreneurship is the solution to solve a problem of unemployment in any economy. Normally, we think of Technology innovations, we think of Engineers from top Technology Institutions. But innovations may also come from Grassroots people. This paper gives the Case study of Nature Technocrats – small business firm of Arvindbhai who has been supported by GIAN (Grassroots Innovations Augmentation Network, Technology Business Incubator for Grassroots Innovations in India. In India, there are many Technology Business Incubation centers but approach of GIAN is unique as it supports Grassroots innovators. This paper has come out of a larger study with Research design: Multiple Embedded Descriptive Case Study. The process of GIAN with unique mechanism of commercializing the Grassroots innovations is described. The problems in this area are also described. This case study may inspire other agencies in India or other countries too for working in the area of Grassroots innovations to Techno-entrepreneurship.   Keywords: Grassroots innovations; Technology innovations; Techno-Entrepreneurship; GIAN; Technology Transfer.

  7. Gian Piero Piretto, La vita privata degli oggetti sovietici. 25 storie da un altro mondo

    Enza Dammiano


    Full Text Available Dopo aver analizzato le “mitologie culturali” dell’era sovietica – il “radioso avvenire” che queste proiettavano (Il radioso avvenire. Mitologie culturali sovietiche, Einaudi, 2001 – e ‘illustrato’, in particolare, gli anni Trenta e Quaranta attraverso Gli occhi di Stalin (Raffaello Cortina, 2010, con La vita privata degli oggetti sovietici Gian Piero Piretto introduce il lettore nelle “storie” di venticinque «cose sovietiche» (32, disseminate lungo l’intero arco temporale di esistenza dell’URSS e oltre: «La maggior parte delle cose a cui dedicherò la mia specifica attenzione ancora circola […], talora in forme rinnovate (degenerate o adattate alla nuova realtà» (43.

  8. Entrevista com Mathieu Dosse, Gian Luigi de Rosa e Michael Kegler

    Andréia Guerini


    Full Text Available O conjunto das três entrevistas que seguem aborda a mesma temática, isto é, aspectos de tradução/adaptação em geral e da tradução do romance Estive em Lisboa e lembrei de você de Luiz Ruffato em particular. O romance de Ruffato foi escrito em 2009, editado em Portugal (Quetzal, 2010 e traduzido para diferentes línguas, como italiano (La Nuova Frontiera, 2011, espanhol (Eterna Cadencia, 2011, francês (Chandeigne, 2015, alemão (Assoziation A, 2016 e, nos próximos meses será publicado em finlandês (Into. O livro foi adaptado para o cinema em 2015, pelo cineasta português José Barahona, sendo exibido em festivais nacionais e internacionais. As entrevistas abaixo foram feitas com os tradutores Gian Luigi De Rosa, Mathieu Dosse e Michael Kegler em 2016. Gian Luigi De Rosa (Itália/1969-- possui doutorado em “Culture e Istituzioni dei paesi di lingue iberiche in età moderna e contemporanea” e é professor de português na Universidade do Salento, em Lecce. É autor de livros e ensaios sobre língua e linguística portuguesa, literatura portuguesa e brasileira e tradução audiovisual e intersemiótica. É também responsável pela elaboração das legendas em italiano do filme Estive em Lisboa e lembrei de você. Mathieu Dosse (Brasil/1978-- é formado pela Université Paris 8, onde estudou Teoria da Tradução. Traduziu para o francês Graciliano Ramos, Luiz Ruffato e João Guimarães Rosa. Michael Kegler (Alemanha/1967-- estudou literatura brasileira e portuguesa na universidade de Frankfurt, sem concluir o curso. Trabalhou como livreiro no Centro do Livro de Língua Portuguesa, antes de se tornar tradutor literário. Traduziu para o alemão José Eduardo Agualusa, Moacyr Scliar, Luiz Ruffato, entre outros autores. Em julho de 2016, junto com Ruffato, recebeu o prêmio literário Hermann Hesse na Alemanha, pela qualidade da obra publicada em conjunto com a sua tradução.

  9. Taevo Gans / Ene Ammer

    Ammer, Ene


    Sisearhitekt Taevo Gansist. Tudengipõlvest, selle aja projektidest, sõpruskonnast, tandemist Summatavet & Gans, Venemaa tellimustest, kaastöölistest. Üksinda Hommilkumaal vene tarbekunsti näitusega 1974. a. 1988. a. loodud perefirmast "GaDis" (omanikud Taevo, Helle Gans, Riia Oja), mis nõustab ka "Wermot" mööbli osas. "GaDise" sisekujundusprojektidest, millega Taevo ja Helle Gans tegelevad üheskoos

  10. Taevo Gans / Ene Ammer

    Ammer, Ene


    Sisearhitekt Taevo Gansist. Tudengipõlvest, selle aja projektidest, sõpruskonnast, tandemist Summatavet & Gans, Venemaa tellimustest, kaastöölistest. Üksinda Hommilkumaal vene tarbekunsti näitusega 1974. a. 1988. a. loodud perefirmast "GaDis" (omanikud Taevo, Helle Gans, Riia Oja), mis nõustab ka "Wermot" mööbli osas. "GaDise" sisekujundusprojektidest, millega Taevo ja Helle Gans tegelevad üheskoos

  11. GaN HEMTs

    Anderson, Jonathan W.; Lee, Kyoung-Keun; Piner, Edwin L.


    Gallium nitride (GaN) has enormous potential for applications in high electron mobility transistors (HEMTs) used in RF and power devices. Intrinsic device properties such as high electron mobility, high breakdown voltage, very high current density, electron confinement in a narrow channel, and high electron velocity in the 2-dimensional electron gas of the HEMT structure are due in large part to the wide band gap of this novel semiconductor material system. This presentation discusses the properties of GaN that make it superior to other semiconductor materials, and outlines the research that will be undertaken in a new program at Texas State University to advance GaN HEMT technology. This program's aim is to further innovate the exceptional performance of GaN through improved material growth processes and epitaxial structure design.

  12. Iglesia de Bonaventura en Monterano, Italia, obra de Gian Lorenzo Bernini : análisis histórico– constructivo y de patologías

    Montoya Molina, Sergio


    El objetivo de este proyecto fin de grado es el diseñar una propuesta viable y sostenible para la rehabilitación de la iglesia y convento de San Bonaventura en Italia. Dado que el autor de este bien de interés cultural es Gian Lorenzo Bernini, un Artista y arquitecto del Barroco tardío italiano de gran prestigio. Éste proyectó y ejecutó edificios y plazas de notable entidad, no solo en la Roma pos imperial, sino en toda Europa. Por ello es obligado que debamos realizar un análi...

  13. Ultra-high Efficiency DC-DC Converter using GaN Devices

    Ramachandran, Rakesh


    The demands for high efficiency dc-dc power converters are increasing day by day in various applications such as telecommunication, data-centers, electric vehicles and various renewable energy systems. Silicon (Si) has been used as the semiconductor material in majority of the power devices...... properties of GaN devices can be utilized in power converters to make them more compact and highly efficient. This thesis entitled “Ultra-high Efficiency DC-DC Converter using GaN devices” focuses on achieving ultra-high conversion efficiency in an isolated dc-dc converter by the optimal utilization of Ga......N devices. Simple replacement of Si or SiC devices with GaN devices in the converter will not give an expected increase in efficiency or any improvement in the performance of the converter. The use of GaN devices has defined another dimension in the design of power converters, which mainly deals...

  14. ARM MJO Investigation Experiment on Gan Island (AMIE-Gan) Science Plan

    Long, CL; Del Genio, A; Deng, M; Fu, X; Gustafson, W; Houze, R; Jakob, C; Jensen, M; Johnson, R; Liu, X; Luke, E; May, P; McFarlane, S; Minnis, P; Schumacher, C; Vogelmann, A; Wang, Y; Webster, P; Xie, S; Zhang, C


    The overarching campaign, which includes the ARM Mobile Facility 2 (AMF2) deployment in conjunction with the Dynamics of the Madden-Julian Oscillation (DYNAMO) and the Cooperative Indian Ocean experiment on intraseasonal variability in the Year 2011 (CINDY2011) campaigns, is designed to test several current hypotheses regarding the mechanisms responsible for Madden-Julian Oscillation (MJO) initiation and propagation in the Indian Ocean area. The synergy between the proposed AMF2 deployment with DYNAMO/CINDY2011, and the corresponding funded experiment on Manus, combine for an overarching ARM MJO Investigation Experiment (AMIE) with two components: AMF2 on Gan Island in the Indian Ocean (AMIE-Gan), where the MJO initiates and starts its eastward propagation; and the ARM Manus site (AMIE-Manus), which is in the general area where the MJO usually starts to weaken in climate models. AMIE-Gan will provide measurements of particular interest to Atmospheric System Research (ASR) researchers relevant to improving the representation of MJO initiation in climate models. The framework of DYNAMO/CINDY2011 includes two proposed island-based sites and two ship-based locations forming a square pattern with sonde profiles and scanning precipitation and cloud radars at both island and ship sites. These data will be used to produce a Variational Analysis data set coinciding with the one produced for AMIE-Manus. The synergy between AMIE-Manus and AMIE-Gan will allow studies of the initiation, propagation, and evolution of the convective cloud population within the framework of the MJO. As with AMIE-Manus, AMIE-Gan/DYNAMO also includes a significant modeling component geared toward improving the representation of MJO initiation and propagation in climate and forecast models. This campaign involves the deployment of the second, marine-capable, AMF; all of the included measurement systems; and especially the scanning and vertically pointing radars. The campaign will include sonde

  15. Basic ammonothermal GaN growth in molybdenum capsules

    Pimputkar, S.; Speck, J. S.; Nakamura, S.


    Single crystal, bulk gallium nitride (GaN) crystals were grown using the basic ammonothermal method in a high purity growth environment created using a non-hermetically sealed molybdenum (Mo) capsule and compared to growths performed in a similarly designed silver (Ag) capsule and capsule-free René 41 autoclave. Secondary ion mass spectrometry (SIMS) analysis revealed transition metal free (<1×1017 cm-3) GaN crystals. Anomalously low oxygen concentrations ((2-6)×1018 cm-3) were measured in a {0001} seeded crystal boule grown using a Mo capsule, despite higher source material oxygen concentrations ((1-5)×1019 cm-3) suggesting that molybdenum (or molybdenum nitrides) may act to getter oxygen under certain conditions. Total system pressure profiles from growth runs in a Mo capsule system were comparable to those without a capsule, with pressures peaking within 2 days and slowly decaying due to hydrogen diffusional losses. Measured Mo capsule GaN growth rates were comparable to un-optimized growth rates in capsule-free systems and appreciably slower than in Ag-capsule systems. Crystal quality replicated that of the GaN seed crystals for all capsule conditions, with high quality growth occurring on the (0001) Ga-face. Optical absorption and impurity concentration characterization suggests reduced concentrations of hydrogenated gallium vacancies (VGa-Hx).

  16. Anelasticity of GaN Epitaxial Layer in GaN LED

    Chung, C. C.; Yang, C. T.; Liu, C. Y.


    In this work, the anelasticity of the GaN layer in the GaN light-emitting-diode device was studied. The present results show that the forward-voltage of GaN LED increases with time, as the GaN light-emitting-diode was maintained at a constant temperature of 100 °C. We found that the increase of the forward-voltage with time attributes to the delay-response of the piezoelectric fields (internal electrical fields in GaN LED device). And, the delay-response of the internal electrical fields with time is caused by the anelasticity (time-dependent strain) of the GaN layer. Therefore, using the correlation of strain-piezoelectric-forward voltage, a plot of thermal strain of the GaN layer against time can be obtained by measuring the forward-voltage of the studied GaN LED against time. With the curves of the thermal strain of GaN epi-layers versus time, the anelasticity of the GaN compound can be studied. The key anelasticity parameter, characteristic relaxation time, of the GaN is defined to be 2623.76 min in this work.

  17. Bandgap engineering of GaN nanowires

    Ming, Bang-Ming; Yan, Hui [College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124 (China); Wang, Ru-Zhi, E-mail:, E-mail: [College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124 (China); Beijing Computational Science Research Center, Beijing, 100094 (China); Yam, Chi-Yung, E-mail:, E-mail: [Beijing Computational Science Research Center, Beijing, 100094 (China); Xu, Li-Chun [College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024 (China); Lau, Woon-Ming [Beijing Computational Science Research Center, Beijing, 100094 (China); Chengdu Green Energy and Green Manufacturing Technology R& D Center, Chengdu, Sichuan, 610207 (China)


    Bandgap engineering has been a powerful technique for manipulating the electronic and optical properties of semiconductors. In this work, a systematic investigation of the electronic properties of [0001] GaN nanowires was carried out using the density functional based tight-binding method (DFTB). We studied the effects of geometric structure and uniaxial strain on the electronic properties of GaN nanowires with diameters ranging from 0.8 to 10 nm. Our results show that the band gap of GaN nanowires depends linearly on both the surface to volume ratio (S/V) and tensile strain. The band gap of GaN nanowires increases linearly with S/V, while it decreases linearly with increasing tensile strain. These linear relationships provide an effect way in designing GaN nanowires for their applications in novel nano-devices.

  18. Epitaxial growth of aligned GaN nanowires and nanobridges


    Homo-epitaxialy grown aligned GaN nanowires were prepared on crystalline GaN mesas. The GaN nanowires showed preferential growth along the 〈100〉 direction (m-axis direction). By using selectively positioned and crystallographically well defined GaN epitaxial lateral overgrowth (ELO) mesas as substrate, we obtained horizontally aligned GaN nanowires, in comb-like arrays and hexagonal network interconnecting the ELO mesas. Preliminary testing of the nanomechanical behavior of horizontal nanowir...

  19. Bulk ammonothermal GaN

    Dwiliński, R.; Doradziński, R.; Garczyński, J.; Sierzputowski, L. P.; Puchalski, A.; Kanbara, Y.; Yagi, K.; Minakuchi, H.; Hayashi, H.


    In this work, results of structural characterization of high-quality ammonothermal GaN are presented. Besides expected low dislocation density (being of the order of 10 3 cm -2) the most interesting feature seems perfect flatness of the crystal lattice of studied crystals. Regardless the size of crystals, lattice curvature radius exceeds 100 m, whereas better crystals reveal radius of several hundred meters and the best above 1000 m. Excellent crystallinity manifests in very narrow X-ray diffraction peaks of full-width at half-maximum (FWHM) values about 16 arcsec.

  20. GaN three dimensional nanostructures

    Dmitriev, V.; Irvin, K. [Cree Research, Inc., Durham, NC (United States); Zubrilov, A.; Tsvetkov, D.; Nikolaev, V. [Cree Research EED, St. Petersburg (Russian Federation); Jakobson, M.; Nelson, D.; Sitnikova, A. [A.F. Ioffe Inst., St. Petersburg (Russian Federation)


    The authors report on the growth and characterization of three dimensional nanoscale structures of GaN. GaN dots were grown by metal organic chemical vapor deposition (MOCVD) on 6H-SiC substrates. The actual size of the dots measured by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) ranged from {approximately}20 nm to more than 2 {micro}m. The average dot density ranged from 10{sup 7} to 10{sup 9} cm{sup {minus}2}. The single crystal structure of the dots was verified by reflectance high energy electron diffraction (HEED) and TEM. Cathodoluminescence (CL) and photoluminescence (PL) of the dots were studied at various temperatures and excitation levels. The PL and CL edge peak for the GaN dots exhibited a blue shift as compared with edge peak position for continuous GaN layers grown on SiC.

  1. GaN Nanowires Synthesized by Electroless Etching Method

    Najar, Adel


    Ultra-long Gallium Nitride Nanowires is synthesized via metal-electroless etching method. The morphologies and optical properties of GaN NWs show a single crystal GaN with hexagonal Wurtzite structure and high luminescence properties.

  2. Synthetic Strategies and Applications of GaN Nanowires

    Guoquan Suo


    Full Text Available GaN is an important III-V semiconductor material with a direct band gap of 3.4 eV at 300 K. The wide direct band gap makes GaN an attractive material for various applications. GaN nanowires have demonstrated significant potential as fundamental building blocks for nanoelectronic and nanophotonic devices and also offer substantial promise for integrated nanosystems. In this paper, we provide a comprehensive review on the general synthetic strategies, characterizations, and applications of GaN nanowires. We first summarize several growth techniques of GaN nanowires. Subsequently, we discuss mechanisms involved to generate GaN nanowires from different synthetic schemes and conditions. Then we review some characterization methods of GaN nanowires. Finally, several kinds of main applications of GaN nanowires are discussed.

  3. Stress distribution of GaN layer grown on micro-pillar patterned GaN templates

    Nagarajan, S.; Svensk, O.; Ali, M.; Naresh-Kumar, G.; Trager-Cowan, C.; Suihkonen, S.; Sopanen, M.; Lipsanen, H.


    High-resolution Raman mapping of the stress distribution in an etched GaN micro-pillar template and a 5 μm thick GaN layer grown on a micro-pillar patterned GaN template is investigated. Raman mapping of the E2 (high) phonon shows differences in stress between the coalescing boundary, the top surface of the pillar region and around the GaN micro-pillar. Increased compressive stress is observed at the coalescing boundary of two adjacent GaN micro-pillars, when compared to the laterally grown GaN regions. The electron channeling contrast image reveals the reduction of threading dislocation density in the GaN layer grown on the micro-pillar patterned GaN template.

  4. High Frequency Performance of GaN Based IMPATT Diodes

    B. Chakrabarti


    Full Text Available IMPATT is a p+n junction diode reversed bias to breakdown and can generate microwave power when properly embedded in a resonant cavity. Till emergence on 1965 day by day it became more powerful solid state source for microwave as well as mm-wave frequency range. To get higher efficiency and power output different structures like SDR, DDR, DAR, lo-high-lo, etc. were proposed and developed by different scientists over the years. Then the IMPATT development started with different semiconductor materials like GaAs, InP, GaN, etc. along with Silicon to achieve higher efficiency, power output and frequency range. In this paper the performance of GaN based SDR IMPATT have thoroughly studied in terms of (i electric field profile[E(x] (iinormalized current density profile [P(x] (iii Susceptance Vs Conductance characteristics (ivRF power output (v negative resistivity profile [R(x] of the diodes through simulation scheme. It is being observed that the efficiency is 17.9% at Ka-band and because of the very high breakdown voltage, power output is as high as1.56W in comparison with other frequency band of operations.

  5. Theoretical study of gallium nitride molecules, GaN2 and GaN4.

    Tzeli, Demeter; Theodorakopoulos, Giannoula; Petsalakis, Ioannis D


    The electronic and geometric structures of gallium dinitride GaN 2, and gallium tetranitride molecules, GaN 4, were systematically studied by employing density functional theory and perturbation theory (MP2, MP4) in conjunction with the aug-cc-pVTZ basis set. In addition, for the ground-state of GaN 4( (2)B 1) a density functional theory study was carried out combining different functionals with different basis sets. A total of 7 minima have been identified for GaN 2, while 37 structures were identified for GaN 4 corresponding to minima, transition states, and saddle points. We report geometries and dissociation energies for all the above structures as well as potential energy profiles, potential energy surfaces and bonding mechanisms for some low-lying electronic states of GaN 4. The dissociation energy of the ground-state GaN 2 ( X (2)Pi) is 1.1 kcal/mol with respect to Ga( (2)P) + N 2( X (1)Sigma g (+)). The ground-state and the first two excited minima of GaN 4 are of (2)B 1( C 2 v ), (2)A 1( C 2 v , five member ring), and (4)Sigma g (-)( D infinityh ) symmetry, respectively. The dissociation energy ( D e) of the ground-state of GaN 4, X (2)B 1, with respect to Ga( (2)P) + 2 N 2( X (1)Sigma g (+)), is 2.4 kcal/mol, whereas the D e of (4)Sigma g (-) with respect to Ga( (4)P) + 2 N 2( X (1)Sigma g (+)) is 17.6 kcal/mol.

  6. Growth and characterisation of GaN

    Li, T


    This thesis describes mainly the studies on growth mechanism of GaN in UHV-MOVPE process, and structural and optical properties of As-doped GaN films grown by PA-MBE. In a novel Thomas Swan growth chamber, we have grown GaN films on Si substrates using TEGa, plasma nitrogen and ammonia. Using a combination of in-situ optical reflectivity and mass spectrometry, we have investigated the parameters controlling the growth process of UHV-MOVPE. In particular we have used sup 1 sup 5 N in order to distinguish gas phase species containing N from those associated purely with metal-organics. We found the surface pyrolysis of TEGa is the rate limiting step, which is similar to GaAs grown by CBE. We also identify the parasitic reactions costing the active nitrogen from plasma, which in turn limits the growth rate. Using Philips X' pert MRD, we have investigated the structural properties of As-doped GaN epitaxial films on sapphire grown by PA-MBE including phase, lattice parameters and mosacity. We have also studied the ...

  7. GaN Micromechanical Resonators with Meshed Metal Bottom Electrode

    Azadeh Ansari


    Full Text Available This work describes a novel architecture to realize high-performance gallium nitride (GaN bulk acoustic wave (BAW resonators. The method is based on the growth of a thick GaN layer on a metal electrode grid. The fabrication process starts with the growth of a thin GaN buffer layer on a Si (111 substrate. The GaN buffer layer is patterned and trenches are made and refilled with sputtered tungsten (W/silicon dioxide (SiO2 forming passivated metal electrode grids. GaN is then regrown, nucleating from the exposed GaN seed layer and coalescing to form a thick GaN device layer. A metal electrode can be deposited and patterned on top of the GaN layer. This method enables vertical piezoelectric actuation of the GaN layer using its largest piezoelectric coefficient (d33 for thickness-mode resonance. Having a bottom electrode also results in a higher coupling coefficient, useful for the implementation of acoustic filters. Growth of GaN on Si enables releasing the device from the frontside using isotropic xenon difluoride (XeF2 etch and therefore eliminating the need for backside lithography and etching.

  8. GaN membrane MSM ultraviolet photodetectors

    Muller, A.; Konstantinidis, G.; Kostopoulos, A.; Dragoman, M.; Neculoiu, D.; Androulidaki, M.; Kayambaki, M.; Vasilache, D.; Buiculescu, C.; Petrini, I.


    GaN exhibits unique physical properties, which make this material very attractive for wide range of applications and among them ultraviolet detection. For the first time a MSM type UV photodetector structure was manufactured on a 2.2 μm. thick GaN membrane obtained using micromachining techniques. The low unintentionally doped GaN layer structure was grown by MOCVD on high resistivity (ρ>10kΩcm) oriented silicon wafers, 500μm thick. The epitaxially grown layers include a thin AlN layer in order to reduce the stress in the GaN layer and avoid cracking. Conventional contact lithography, e-gun Ni/Au (10nm /200nm) evaporation and lift-off techniques were used to define the interdigitated Schottky metalization on the top of the wafer. Ten digits with a width of 1μm and a length of 100μm were defined for each electrode. The distance between the digits was also 1μm. After the backside lapping of the wafer to a thickness of approximately 150μm, a 400nm thick Al layer was patterned and deposited on the backside, to be used as mask for the selective reactive ion etching of silicon. The backside mask, for the membrane formation, was patterned using double side alignment techniques and silicon was etched down to the 2.2μm thin GaN layer using SF 6 plasma. A very low dark current (30ρA at 3V) was obtained. Optical responsivity measurements were performed at 1.5V. A maximum responsivity of 18mA/W was obtained at a wavelength of 370nm. This value is very good and can be further improved using transparent contacts for the interdigitated structure.

  9. GaN Nanowire Arrays for High-Output Nanogenerators

    Huang, Chi-Te


    Three-fold symmetrically distributed GaN nanowire (NW) arrays have been epitaxially grown on GaN/sapphire substrates. The GaN NW possesses a triangular cross section enclosed by (0001), (2112), and (2112) planes, and the angle between the GaN NW and the substrate surface is ∼62°. The GaN NW arrays produce negative output voltage pulses when scanned by a conductive atomic force microscope in contact mode. The average of piezoelectric output voltage was about -20 mV, while 5-10% of the NWs had piezoelectric output voltages exceeding -(0.15-0.35) V. The GaN NW arrays are highly stable and highly tolerate to moisture in the atmosphere. The GaN NW arrays demonstrate an outstanding potential to be utilized for piezoelectric energy generation with a performance probably better than that of ZnO NWs. © 2010 American Chemical Society.

  10. Gallium Nitride (GaN) High Power Electronics (FY11)


    for HPE GaN high electron mobility transistors ( HEMTs ) compared to SiC metal-oxide-semiconductor field effect transistors (MOSFETs). Although a few...Figure 16. Asymmetric rocking curve for an HVPE film grown on an HVPE substrate. ............19 Figure 17. Schematic of a GaN /AlGaN HEMT structure grown...frequency (RF) HEMTs . These considerable investments can be leveraged for GaN HPE. Some people are concerned about the relative scarcity of gallium

  11. Temperature Dependence of GaN HEMT Small Signal Parameters


    original work is properly cited. This study presents the temperature dependence of small signal parameters of GaN /SiC HEMTs across the 0–150◦C range...the performance of GaN /SiC device, two state-of-the-art AlGaN/ GaN HEMT devices were characterized at −25, 25, 75, and 125◦C base plate (on-wafer...number. 1. REPORT DATE NOV 2011 2. REPORT TYPE 3. DATES COVERED 00-00-2011 to 00-00-2011 4. TITLE AND SUBTITLE Temperature Dependence of GaN HEMT

  12. Amphoteric arsenic in GaN

    Wahl, U; Araújo, J P; Rita, E; Soares, JC


    We have determined the lattice location of implanted arsenic in GaN by means of conversion electron emission channeling from radioactive $^{73}$As. We give direct evidence that As is an amphoteric impurity, thus settling the long-standing question as to whether it prefers cation or anion sites in GaN. The amphoteric character of As and the fact that As$\\scriptstyle_{Ga}\\,$ " anti-sites ” are not minority defects provide additional aspects to be taken into account for an explanantion of the so-called “ miscibility gap ” in ternary GaAs$\\scriptstyle_{1-x}$N$\\scriptstyle_{x}$ compounds, which cannot be grown with a single phase for values of $x$ in the range 0.1<${x}$< 0.99.

  13. Influence of growth pressure of a GaN buffer layer on the properties of MOCVD GaN

    CHEN; Jun(陈俊); ZHANG; Shuming(张书明); ZHANG; Baoshun(张宝顺); ZHU; Jianjun(朱建军); FENG; Gan(冯淦); DUAN; Lihong(段俐宏); WANG; Yutian(王玉田); YANG; Hui(杨辉); ZHENG; Wenchen(郑文琛)


    The influence of growth pressure of GaN buffer layer on the properties of MOCVD GaN on α-Al2O3 has been investigated with the aid of a home-made in situ laser reflectometry measurement system. The results obtained with in situ measurements and scanning electron microscope show that with the increase in deposition pressure of buffer layer, the nuclei increase in size, which roughens the surface, and delays the coalescence of GaN nuclei. The optical and crystalline quality of GaN epilayer was improved when buffer layer was deposited at high pressure.

  14. Growth of Strain Free GaN Layers on (0001) Oriented Sapphire by Using Quasi-Porous GaN Template

    XIE Xin-Jian; CHEN Jia-Rong; CAO Xian-Cun; ZHONG Fei; QIU Kai; LIU Gui-Feng; YIN Zhi-Jun; WANG Yu-Qi; LI Xin-Hua; JI Chang-Jian; HAN Qi-Fen


    We report the reduced-strain gallium-nitride (GaN) epitaxial growth on (0001) oriented sapphire by using quasi-porous GaN template. A GaN film in thickness of about 1μm was initially grown on a (0001) sapphire substrate by molecular beam epitaxy. Then it was dealt by putting, into 45% NaOH solution at 100°C for Wmin. By this process a quasi-porous GaN Rim was formed. An epitaxial GaN layer was grown on the porous GaN layer at 1050°C in the hydride vapour phase epitaxy reactor. The epitaxial layer grown on the porous GaN is found to have no cracks on the surface. That is much improved from many cracks on the surface of the GaN epitaxial layer grown on the sapphire as the same as on GaN buffer directly.

  15. Day to day with COPD

    COPD - day to day; Chronic obstructive airways disease - day to day; Chronic obstructive lung disease - day to ... Having COPD can sap your energy. These simple changes can make your days easier and preserve your strength. Ask ...

  16. Preparation and Characterization of GaN Nanowires

    薛成山; 杨莺歌; 马洪磊; 庄惠照; 马瑾


    GaN Nanowires were prepared by the post-nitridation technique. The morphology and structure of GaN nanowires are investigated by transmission-electron microscopy and scanning electron microscopy. A strong blue photoluminescence is observed for room-temperature measurement, which attributes to electron transition from DX centre to valence band.

  17. Silicon—a new substrate for GaN growth

    S Pal; C Jacob


    Generally, GaN-based devices are grown on silicon carbide or sapphire substrates. But these substrates are costly and insulating in nature and also are not available in large diameter. Silicon can meet the requirements for a low cost and conducting substrate and will enable integration of optoelectronic or high power electronic devices with Si based electronics. But the main problem that hinders the rapid development of GaN devices based on silicon is the thermal mismatch of GaN and Si, which generates cracks. In 1998, the first MBE grown GaN based LED on Si was made and now the quality of material grown on silicon is comparable to that on sapphire substrate. It is only a question of time before Si based GaN devices appear on the market. This article is a review of the latest developments in GaN based devices on silicon.

  18. Synthesis of GaN films on porous silicon substrates


    A novel and simple method was employed to synthesize GaN films on porous silicon (PS) substrates. GaN films were obtained through the reaction between NH3 and Ga2O3 films deposited on the substrates with magnetron sputtering.Since GaN and PS are all good materials for luminescence, it is expected to obtain some new properties from GaN on PS.The samples were analyzed with X-ray diffraction (XRD) to identify crystalline structure. Fourier transmit infrared (FTIR)spectrum was used to analyze the chemical state of the samples. The films were observed with scanning electron microscopy (SEM) and were found to consist of many big crystal grains. Photoluminescence (PL) spectrum was used to illuminate the optical property of the GaN films.

  19. Atomic force microscopy studies of homoepitaxial GaN layers grown on GaN template by laser MBE

    Choudhary, B. S. [CSIR-National Physical Laboratory, Dr K.S. Krishnan Road, New Delhi 110012 (India); Rajasthan Technical University, Rawatbhata Road, Kota 324010 (India); Singh, A.; Tyagi, P. K. [Department of Applied Physics, Delhi Technological University, Delhi 110042 (India); Tanwar, S. [Rajasthan Technical University, Rawatbhata Road, Kota 324010 (India); Kumar, M. Senthil; Kushvaha, S. S., E-mail: [CSIR-National Physical Laboratory, Dr K.S. Krishnan Road, New Delhi 110012 (India)


    We have grown homoepitaxial GaN films on metal organic chemical vapor deposition (MOCVD) grown 3.5 µm thick GaN on sapphire (0001) substrate (GaN template) using an ultra-high vacuum (UHV) laser assisted molecular beam epitaxy (LMBE) system. The GaN films were grown by laser ablating a polycrystalline solid GaN target in the presence of active r.f. nitrogen plasma. The influence of laser repetition rates (10-30 Hz) on the surface morphology of homoepitaxial GaN layers have been studied using atomic force microscopy. It was found that GaN layer grown at 10 Hz shows a smooth surface with uniform grain size compared to the rough surface with irregular shape grains obtained at 30 Hz. The variation of surface roughness of the homoepitaxial GaN layer with and without wet chemical etching has been also studied and it was observed that the roughness of the film decreased after wet etching due to the curved structure/rough surface.

  20. Nonlinear characterization of GaN HEMT

    Chen Chi; Hao Yue; Yang Ling; Quan Si; Ma Xiaohua; Zhang Jincheng, E-mail: [National Key Laboratory of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi' an 710071 (China)


    DC I-V output, small signal and an extensive large signal characterization (load-pull measurements) of a GaN HEMT on a SiC substrate with different gate widths of 100 {mu}m and 1 mm have been carried out. From the small signal data, it has been found that the cutoff frequencies increase with gate width varying from 100 {mu}m to 1mm, owing to the reduced contribution of the parasitic effect. The devices investigated with different gate widths are enough to work in the C band and X band. The large signal measurements include the load-pull measurements and power sweep measurements at the C band (5.5 GHz) and X band (8 GHz). When biasing the gate voltage in class AB and selecting the source impedance, the optimum load impedances seen from the device for output power and PAE were localized in the load-pull map. The results of a power sweep at an 8 GHz biased various drain voltage demonstrate that a GaN HEMT on a SiC substrate has good thermal conductivity and a high breakdown voltage, and the CW power density of 10.16 W/mm was obtained. From the results of the power sweep measurement at 5.5 GHz with different gate widths, the actual scaling rules and heat effect on the large periphery device were analyzed, although the effects are not serious. The measurement results and analyses prove that a GaN HEMT on a SiC substrate is an ideal candidate for high-power amplifier design.

  1. GaN: Defect and Device Issues

    Pearton, S.J.; Ren, F.; Shul, R.J.; Zolper, J.C.


    The role of extended and point defects, and key impurities such as C, O and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

  2. A Strategic Review of Reduction o Dislocation Density at The Heterogenious Junction of GaN Epilayer on Foreign Substrate

    S.Das Bhattacharyya


    Full Text Available Now-a-days for long range microwave communication, especially for space applications, devices capable to operate at a high power and high frequency are desired. Compound Semiconductor (CS, mainly Gallium Nitride (GaN based heterostructure electronic devices are the only available solutions till now to fulfil these criteria. However, looking from a cost and manufacturing perspective, GaN substrate has considerable drawbacks like non-availability, expense as well as compulsion to use older technologies for device designing as the wafer diameter is small. A potential solution for performance/cost dilemma is to grow high quality GaN as active layer on a well matured substrate by metamorphic technique. Metamorphic buffer technology allows the device designer an additional degree of freedom to optimize the transistor at high frequency for high gain and power applications. But this metamorphic buffer technology has some drawbacks, too. The main limiting factor for this technology is the propensity to develop dislocation at the heterojunction due to lattice mismatch between the grown layer and the substrate. A good quality metamorphic buffer can only be achieved by reduction of dislocation density at the heterojunction. This paper reviews the progress being made towards reduction of dislocation density of GaN based devices grown on Silicon Carbide (SiC, Sapphire (Al2O3 and Si substrate, respectively, in terms of material parameters and growth issues.

  3. III-nitride grown on freestanding GaN nanostructures

    Wang, Yongjin; Zhu, Hongbo [Institute of Communication Technology, Nanjing University of Posts and Telecommunications, Nanjing, Jiang-Su 210003 (China); Hu, Fangren; Hane, Kazuhiro [Department of Nanomechanics, Tohoku University, Sendai 980-8579 (Japan)


    We report here the epitaxial growth of III-nitride on the freestanding GaN nanostructures by molecular beam epitaxy growth. Various GaN nanostructures are defined by electron beam lithography and realized on GaN-on-silicon substrate by fast atom beam etching. Silicon substrate beneath GaN nanostructures is removed from the backside to form the freestanding GaN slab, and the epitaxial growth of III-nitride by MBE is performed on the prepared GaN template. The selective growth takes place with the assistance of GaN nanostructures and generates hexagonal III-nitride pyramids. Thin epitaxial structures, depending on the shape and the size of GaN nanostructure, can produce the promising optical performance. This work opens the way to combine silicon micromachining with the epitaxial growth of III-nitride by MBE on GaN-on-silicon substrate for further integrated optics (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Growth and Microstructure of GaN on (111) Si

    Follstaedt, D. M.; Han, J.; Provencio, P.; Fleming, J.


    GaN grown on (111) Si by MOCVD was examined by TEM. This structure is of interest for possible integration of short-wavelength optical emission with Si microelectronics. A rotating disc reactor with TMGa, TMAl and ammonia precursors was used to first grow an 30 nm-thick AlN buffer on the Si at 1080^oC, followed by GaN at 1060^oC. The resulting 2 μm layer appeared smooth by in situ reflectance, but developed a high density of cracks when cooled to room temperature due to the difference in thermal expansions of GaN and Si. Between the cracks, cross-section and plan-view TEM identified the orientation as (0001)GaN parallel (111)Si, with [11-20]GaN parallel [1-10]Si. A high density of threading dislocations (4 to 8x10^9/cm^2) was found and determined to be 2/3 pure edge and 1/3 mixed (edge + screw) in character. A low density (10^8/cm^2) of nanotubes was also identified. This defect microstructure is much like that of GaN on sapphire. The thin AlN buffer was continuous and consists of 20 to 40 nm grains, with some exhibiting slight misorientations. A few dislocations threading the GaN layer could be traced to an interface between the AlN grains. The continuous thin layer indicates that the AlN buffer "wets" Si, whereas thin GaN layers are discontinuous on sapphire; 0.4 μm thickness of GaN is needed for a continuous layer.

  5. UMA/GAN network architecture analysis

    Yang, Liang; Li, Wensheng; Deng, Chunjian; Lv, Yi


    This paper is to critically analyze the architecture of UMA which is one of Fix Mobile Convergence (FMC) solutions, and also included by the third generation partnership project(3GPP). In UMA/GAN network architecture, UMA Network Controller (UNC) is the key equipment which connects with cellular core network and mobile station (MS). UMA network could be easily integrated into the existing cellular networks without influencing mobile core network, and could provides high-quality mobile services with preferentially priced indoor voice and data usage. This helps to improve subscriber's experience. On the other hand, UMA/GAN architecture helps to integrate other radio technique into cellular network which includes WiFi, Bluetooth, and WiMax and so on. This offers the traditional mobile operators an opportunity to integrate WiMax technique into cellular network. In the end of this article, we also give an analysis of potential influence on the cellular core networks ,which is pulled by UMA network.

  6. Investigation of deep levels in bulk GaN


    The first gallium nitride (GaN) crystal was grown by hydride vapor phase epitaxy in 1969 by Maruska and Tietjen and since then, there has been an intensive development of the field, especially after the ground breaking discoveries concerning growth and p-type doping of GaN done by the 2014 year Nobel Laureates in Physics, Isamu Akasaki, Hiroshi Amano and Shuji Nakamura. GaN and its alloys with In and Al belong to a semiconductor group which is referred as the III-nitrides. It has outstanding ...

  7. Synthesis of Single Crystal GaN Nanowires

    Lining Fang


    Full Text Available The straight and curved gallium nitride (GaN nanowires were successfully synthesized by controlling the gallium/ nitrogen reactant ratio via a chemical vapour deposition method. The structure and morphology of nanowires were characterized by X-ray diffraction (XRD, transmission electronic microscopy (TEM, field emission scanning electron microscopy (FESEM, selected area electron diffraction (SAED and high resolution transmission electron microscopy (HRTEM. The straight and curved GaN nanowires are composed of wurtzite and a zinc blende structure, respectively. Photoluminescence (PL spectra of zinc blende GaN nanowires showed a strong UV emission band at 400 nm, indicating potential application in optoe‐ lectronic devices.

  8. GaN transistors for efficient power conversion

    Lidow, Alex; de Rooij, Michael; Reusch, David


    The first edition of GaN Transistors for Efficient Power Conversion was self-published by EPC in 2012, and is currently the only other book to discuss GaN transistor technology and specific applications for the technology. More than 1,200 copies of the first edition have been sold through Amazon or distributed to selected university professors, students and potential customers, and a simplified Chinese translation is also available. The second edition has expanded emphasis on applications for GaN transistors and design considerations. This textbook provides technical and application-focused i

  9. [Changes of HPAA in Different Rat Models of Gan Stagnation, Pi Deficiency, Gan Stagnation Pi Defi- ciency and Interventional Effect of Chaishu Sijun Decoction].

    Zhao, Rong-hua; Liu, Jin-na; Li, Cong; Zhang, Jing-sheng; Wang, Bang-zhong; Yao, Yuan-chao; Xie, Ming; Wang, Dao-han


    To compare changes of hypothalamus-pituitary-adrenal axis (HPAA) in different rat models of Gan stagnation (GS), Pi deficiency (PD), Gan stagnation Pi deficiency (GSPD) syndromes, and to observe interventional effect of Chaishu Sijun Decoction (CSD, capable of soothing Gan-qi invigorating Pi) on them. Seventy Wistar rats were divided into the normal control group (group 1), the GS group (group 2), the PD group (group 3), the GSPD group (group 4), the GS intervention group (group 5), the PD intervention group (group 6), and the GSPD intervention group (group 7) according to random digit table, 10 in each group. Rats in group 1 received no treatment. Rats in group 2 and 5 were modeled by chronic restraint method. Rats in group 3 and 6 were modeled by excess fatigue plus alimentary abstinence method. Rats in group 4 and 7 were modeled by chronic restraint, excess fatigue, and alimentary abstinence method. At the 2nd weekend of modeling, CSD at 2.86 g/kg was fed to rats in group 5, 6, and 7 by gastrogavage for 2 successive weeks. Equal volume of distilled water was given to rats in the rest 4 groups. On the 29th day, rats were killed, adrenal weight weighed, and adrenal index calculated. Levels of plasma and hypothalamus corticotropin-releasing hormone (CRH), plasma and pituitary adrenocorticotrophic hormone (ACTH), and plasma corticosterone (CORT) were determined using radioimmunity. Compared with group 1, adrenal index significantly decreased in group 2, 3, and 4 (P HPAA, but with optimal effect on GSPD syndrome. CSD had higher correlation with GSPD syndrome.

  10. Annealing of ion-implanted GaN

    Burchard, A; Stötzler, A; Weissenborn, R; Deicher, M


    $^{111m}$Cd and $^{112}$Cd ions have been implanted into GaN. With photoluminescence spectroscopy and perturbed $\\gamma-\\gamma$-angular correlation spectroscopy (PAC) the reduction of implantation damage and the optical activation of the implants have been observed as a function of annealing temperature using different annealing methods. The use of N$_{2}$ or NH$_{3}$ atmosphere during annealing allows temperatures up to 1323k and 1373 K, respectively, but above 1200 K a strong loss of Cd from the GaN has been observed. Annealing GaN together with elementary Al forms a protective layer on the GaN surface allowing annealing temperatures up to 1570 K for 10 min. (11 refs).

  11. Application of Generative Adversarial Networks (GANs) to jet images

    CERN. Geneva

    2017-01-01 We provide a bridge between generative modeling in the Machine Learning community and simulated physical processes in High Energy Particle Physics by applying a novel Generative Adversarial Network (GAN) architecture to the production of jet images -- 2D representations of energy depositions from particles interacting with a calorimeter. We propose a simple architecture, the Location-Aware Generative Adversarial Network, that learns to produce realistic radiation patterns from simulated high energy particle collisions. The pixel intensities of GAN-generated images faithfully span over many orders of magnitude and exhibit the desired low-dimensional physical properties (i.e., jet mass, n-subjettiness, etc.). We shed light on limitations, and provide a novel empirical validation of image quality and validity of GAN-produced simulations of the natural world. This work provides a base for further explorations of GANs for use in faster simulation in High Energy Particle Physics.

  12. Thickness measurement of GaN epilayer using high resolution X-ray diffraction technique

    冯淦; 朱建军; 沈晓明; 张宝顺; 赵德刚; 王玉田; 杨辉; 梁骏吾


    In this paper we propose a new method for measuring the thickness of the GaN epilayer, by using the ratio of the integrated intensity of the GaN epilayer X-ray diffraction peaks to that of the sapphire substrate ones. This ratio shows a linear dependence on the GaN epilayer thickness up to 2 μm. The new method is more accurate and convenient than those of using the relationship between the integrated intensity of GaN epilayer diffraction peaks and the GaN thickness. Besides, it can eliminate the absorption effect of the GaN epilayer.

  13. GaN nanorods coated with pure BN

    Han, Wei-Qiang; Zettl, A.


    We report a method to efficiently synthesize gallium nitride (GaN) nanorods coated with insulating boron nitride (BN) layers. The GaN core is crystalline (with either a cubic zincblende or hexagonal wurtzite structure) and has diameters ranging from 10 to 85 nm and lengths up to 60 μm. The outer encapsulating BN shells with typical thicknesses less than 5 nm extend fully over, and adhere well to, the entire nanorod surface.

  14. Effect of photocatalytic oxidation technology on GaN CMP

    Wang, Jie, E-mail:; Wang, Tongqing, E-mail:; Pan, Guoshun, E-mail:; Lu, Xinchun, E-mail:


    Graphical abstract: - Highlights: • Photocatalytic oxidation technology was introduced to GaN CMP for the first time and proves to be more efficient than before. • XPS analysis reveals the planarization process by different N-type semiconductor particles. • Analyzing the effect of pH on photocatalytic oxidation in GaN CMP. • Proposing the photocatalytic oxidation model to reveal the removal mechanism. - Abstract: GaN is so hard and so chemically inert that it is difficult to obtain a high material removal rate (MRR) in the chemical mechanical polishing (CMP) process. This paper discusses the application of photocatalytic oxidation technology in GaN planarization. Three N-type semiconductor particles (TiO{sub 2}, SnO{sub 2}, and Fe{sub 2}O{sub 3}) are used as catalysts and added to the H{sub 2}O{sub 2}–SiO{sub 2}-based slurry. By optical excitation, highly reactive photoinduced holes are produced on the surface of the particles, which can oxidize OH{sup −} and H{sub 2}O absorbed on the surface of the catalysts; therefore, more OH* will be generated. As a result, GaN MRRs in an H{sub 2}O{sub 2}–SiO{sub 2}-based polishing system combined with catalysts are improved significantly, especially when using TiO{sub 2}, the MRR of which is 122 nm/h. The X-ray photoelectron spectroscopy (XPS) analysis shows the variation trend of chemical composition on the GaN surface after polishing, revealing the planarization process. Besides, the effect of pH on photocatalytic oxidation combined with TiO{sub 2} is analyzed deeply. Furthermore, the physical model of GaN CMP combined with photocatalytic oxidation technology is proposed to describe the removal mechanism of GaN.

  15. Terahertz response of GaN thin films.

    Tsai, Tsong-Ru; Chen, Shi-Jie; Chang, Chih-Fu; Hsu, Sheng-Hsien; Lin, Tai-Yuan; Chi, Cheng-Chung


    The indices of refraction, extinction constants and complex conductivities of the GaN film for frequencies ranging from 0.2 to 2.5 THz are obtained using THz time-domain spectroscopy. The results correspond well with the Kohlrausch stretched exponential model. Using the Kohlrausch model fit not only provides the mobility of the free carriers in the GaN film, but also estimates the relaxation time distribution function and average relaxation time.

  16. Study of GaN adsorption on the Si surface

    Li Wei, E-mail: [Laboratory of Quantum Information Technology, School of Physics and Telecommunication Engineering, South China Normal University, 510006 Guangzhou (China); Chen Junfang [Laboratory of Quantum Information Technology, School of Physics and Telecommunication Engineering, South China Normal University, 510006 Guangzhou (China); Wang Teng [School of Computer, South China Normal University, 510006 Guangzhou (China)


    The adsorption energy, the band structures and DOS (density of states) of GaN on surface of Si(1 0 0) and Si(1 1 1) are calculated by the first-principle using plane-wave pseudo-potentials method based on the density functional theory in order to know the adsorption between the surface of Si and GaN. The calculation results show that GaN is easier adsorbed on the surface of Si(1 0 0) than the surface of Si(1 1 1) under the same experimental condition. There are strong charge distributions between N and Si atom. The bandgap of GaN on surface of Si(1 0 0) becomes a little narrower than that of pure GaN. On the other hand, GaN film is deposited on the surface of Si(1 0 0) by ECR-MOPECVD (electron cyclotron resonance-plasma enhanced chemical vapor deposition) at low temperature. For substrate of Si(1 1 1), no film is obtained under the same experimental condition.

  17. Void shape control in GaN re-grown on hexagonally patterned mask-less GaN

    Ali, M.; Romanov, A. E.; Suihkonen, S.; Svensk, O.; Törmä, P. T.; Sopanen, M.; Lipsanen, H.; Odnoblyudov, M. A.; Bougrov, V. E.


    We present the results of GaN re-growth on hexagonally patterned GaN templates. Sapphire was used as the original substrate and the samples were grown by metalorganic vapor phase epitaxy (MOVPE). The re-growth on the patterned templates results in the formation of voids at the GaN/sapphire interface. Our extensive scanning electron microscopy (SEM)-based experimental investigations show that the void shape can be controlled from nearly vertical to fully inclined configurations. It was found that the initial hexagon hole diameter plays a key role in determining the final profile of the void sidewalls. X-ray diffraction analysis of the GaN layers indicates that the layers with inclined sidewall voids have an improved crystalline quality. Knowledge of the void configurations in the GaN layers and a possibility to control their shape can help in enhancing light extraction from the light emitting structures.

  18. May Day



    For Teacher: May Day occurs in May 1 and refers to any of several public holidays.In many countries, May Day is synonymous(同义词的)with International Workers' Day, or Labor Day, which celebrates the social and economic achievements(成就)of the labor movement.

  19. May Day



    For Teachers: May Day occurs on May 1 and refers to any of several public holidays. In many coun- tries, May Day is synonymous (同义词的) with International Workers' Day, or Labor Day, which celebrates the social and economic achievements (成就) of the labor movement. As a day of celebration, the holiday has an- cient origins (起源), and it can relate to many customs that have survived into modem times.

  20. DLTS study of n-type GaN grown by MOCVD on GaN substrates

    Tokuda, Y.; Matsuoka, Y.; Ueda, H.; Ishiguro, O.; Soejima, N.; Kachi, T.


    Electron traps in n-type GaN layers grown homoepitaxially by MOCVD on free-standing GaN substrates have been characterized using DLTS for vertical Schottky diodes. Two free-standing HVPE GaN substrates (A and B), obtained from two different sources, are used. The Si-doped GaN layers with the thickness of 5 μm are grown on an area of 0.9×0.9 cm 2 of substrate A and on an area of 1×1 cm 2 of substrate B. Two traps labeled B1 (Ec-0.23 eV) and B2 (Ec-0.58 eV) are observed with trap B2 dominant in GaN on both substrates. There exist no dislocation-related traps which have been previously observed in MOCVD GaN on sapphire. This might be correlated to the reduction in dislocation density due to the homoepitaxial growth. However, it is found that there is a large variation, more than an order of magnitude, in trap B2 concentration and that the B2 spatial distributions are different between the two substrates used.

  1. GaN Bulk Growth and Epitaxy from Ca-Ga-N Solutions Project

    National Aeronautics and Space Administration — This SBIR proposal addresses the liquid phase epitaxy (LPE) of gallium nitride (GaN) films using nitrogen-enriched metal solutions. Growth of GaN from solutions...

  2. Thick Homoepitaxial GaN with Low Carrier Concentration for High Blocking Voltage


    demonstrated that GaN Schottky diodes fabricated on freestanding GaN substrates with simple metal overlap edge termination show reverse recovery time...Prior to ramping up to the growth temperature for MOCVD deposition of GaN, the flows of palladium -diffused high purity hydrogen and ammonia were

  3. Tailoring GaN semiconductor surfaces with biomolecules.

    Estephan, Elias; Larroque, Christian; Cuisinier, Frédéric J G; Bálint, Zoltán; Gergely, Csilla


    Functionalization of semiconductors constitutes a crucial step in using these materials for various electronic, photonic, biomedical, and sensing applications. Within the various possible approaches, selection of material-binding biomolecules from a random biological library, based on the natural recognition of proteins or peptides toward specific material, offers many advantages, most notably biocompatibility. Here we report on the selective functionalization of GaN, an important semiconductor that has found broad uses in the past decade due to its efficient electroluminescence and pronounced chemical stability. A 12-mer peptide ("GaN_probe") with specific recognition for GaN has evolved. The subtle interplay of mostly nonpolar hydrophobic and some polar amino acidic residues defines the high affinity adhesion properties of the peptide. The interaction forces between the peptide and GaN are quantified, and the hydrophobic domain of the GaN_probe is identified as primordial for the binding specificity. These nanosized binding blocks are further used for controlled placement of biotin-streptavidin complexes on the GaN surface. Thus, the controlled grow of a new, patterned inorganic-organic hybrid material is achieved. Tailoring of GaN by biological molecules can lead to a new class of nanostructured semiconductor-based devices.

  4. Macro-pyramid in GaN Film

    ZHOU Jing; YANG Zhi-Jian; XU Shi-Fa; ZHU Xing; ZHANG Guo-Yi


    A thin film of GaN with the thickness of 1.0μm was grown on α-Al2Oa substrate by metal organic chemical vapour disposition and then a thick GaN film with thickness of 12μm was grown in the halide vapour phase epitaxy system. Some macro-pyramids appeared on the surface of the sample. The macro-pyramids made the surfaceof the GaN film rough, which was harmful to the devices made by GaN materials. These defects changed the distribution of carrier concentration and affected the optical properties of GaN. The step height of the pyramids was about 30-40 nm measured by atomic force microscopy. A simple model was proposed to explain the macro- pyramid phenomenon compared with the growth spiral The growth of the macro-pyramid was relative to the physical conditions in the reaction zone. Both increasing growth temperature and low pressure may reduce the pyramid size.

  5. GaN on sapphire mesa technology

    Herfurth, Patrick; Men, Yakiv; Kohn, Erhard [Institute of Electron Devices and Circuits, Ulm University, Albert-Einstein Allee 45, 89081 Ulm (Germany); Roesch, Rudolph [Institute of Optoelectronics, Albert-Einstein Allee 45, 89081 Ulm (Germany); Carlin, Jean-Francois; Grandjean, Nicolas [Laboratory of Advanced Semiconductors for Photonics and Electronics, Ecole Polytechnique Federal de Lausanne, 1015 Lausanne (Switzerland)


    This contribution reports on a GaN on sapphire mesa technology for lattice matched InAlN/GaN HEMTs similar to a silicon on insulator technology. Ultrathin buffer layers between 500 nm and 100 nm have been deep mesa etched down to the substrate to avoid cross talk between devices through the buffer and provide full transparency outside the active device area (of special interest to biochemical sensor applications).The heterostructure characteristics were: N{sub S}> 1.6 x 10{sup 13} cm{sup -2}, R{sub sh}< 600 {omega}/{open_square}. 0.25 {mu}m gate length HEMT device characteristics are moderate, but essentially similar down to 200 nm buffer thickness. Devices on 100 nm buffer layer are still difficult to reproduce. I{sub on}/I{sub off} was up to 10{sup 9} and sub-threshold slopes down to 90 mV/dec (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. High Voltage GaN Schottky Rectifiers



    Mesa and planar GaN Schottky diode rectifiers with reverse breakdown voltages (V{sub RB}) up to 550V and >2000V, respectively, have been fabricated. The on-state resistance, R{sub ON}, was 6m{Omega}{center_dot} cm{sup 2} and 0.8{Omega}cm{sup 2}, respectively, producing figure-of-merit values for (V{sub RB}){sup 2}/R{sub ON} in the range 5-48 MW{center_dot}cm{sup -2}. At low biases the reverse leakage current was proportional to the size of the rectifying contact perimeter, while at high biases the current was proportional to the area of this contact. These results suggest that at low reverse biases, the leakage is dominated by the surface component, while at higher biases the bulk component dominates. On-state voltages were 3.5V for the 550V diodes and {ge}15 for the 2kV diodes. Reverse recovery times were <0.2{micro}sec for devices switched from a forward current density of {approx}500A{center_dot}cm{sup -2} to a reverse bias of 100V.

  7. CEMI Days



    CEMI Days are an important channel of engagement between DOE and the manufacturing industry to identify challenges and opportunities for increasing U.S. manufacturing competitiveness. CEMI Days that are held at manufacturing companies’ facilities can include tours of R&D operations or other points of interest determined by the host company.

  8. Dinosaur Day!

    Nakamura, Sandra; Baptiste, H. Prentice


    In this article, the authors describe how they capitalized on their first-grade students' love of dinosaurs by hosting a fun-filled Dinosaur Day in their classroom. On Dinosaur Day, students rotated through four dinosaur-related learning stations that integrated science content with art, language arts, math, and history in a fun and time-efficient…

  9. Synthesis and Characterization of Glomerate GaN Nanowires

    Xue Chengshan


    Full Text Available Abstract Glomerate GaN nanowires were synthesized on Si(111 substrates by annealing sputtered Ga2O3/Co films under flowing ammonia at temperature of 950 °C. X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy and Fourier transformed infrared spectra were used to characterize the morphology, crystallinity and microstructure of the as-synthesized samples. Our results show that the samples are of hexagonal wurtzite structure. For the majority of GaN nanowires, the length is up to tens of microns and the diameter is in the range of 50–200 nm. The growth process of the GaN nanowires is dominated by Co–Ga–N alloy mechanism.

  10. Gallium incorporation kinetics during GSMBE of GaN

    Jones, C.R.; Kaspi, R. [Wright State Univ. Research Center, Dayton, OH (United States); Lei, T.; Evans, K.R. [Wright Lab., Wright-Patterson AFB, OH (United States). Solid State Electronics Directorate


    The kinetics of Ga incorporation during gas-source molecular beam epitaxy of GaN are investigated for varying substrate temperature and incident ammonia flux. Incident Ga atoms eventually either: (1) react with NH{sub 3} to form GaN; (2) accumulate on the film surface, or (3) desorb. Low substrate temperatures lead to significant Ga surface accumulation due to the temperature-dependent reactivity of NH{sub 3} towards Ga. High substrate temperatures give rise to significant Ga desorption. Increasing NH{sub 3} flux retards both Ga surface accumulation and Ga desorption. The GaN formation rate variation with substrate temperature peaks near 750 C and increases with NH{sub 3} flux. The observation of two distinct and very low activation energies for Ga desorption suggests a relatively complex surface chemistry and a strong likelihood that hydrogen is playing an important role.

  11. High-Sensitivity GaN Microchemical Sensors

    Son, Kyung-ah; Yang, Baohua; Liao, Anna; Moon, Jeongsun; Prokopuk, Nicholas


    Systematic studies have been performed on the sensitivity of GaN HEMT (high electron mobility transistor) sensors using various gate electrode designs and operational parameters. The results here show that a higher sensitivity can be achieved with a larger W/L ratio (W = gate width, L = gate length) at a given D (D = source-drain distance), and multi-finger gate electrodes offer a higher sensitivity than a one-finger gate electrode. In terms of operating conditions, sensor sensitivity is strongly dependent on transconductance of the sensor. The highest sensitivity can be achieved at the gate voltage where the slope of the transconductance curve is the largest. This work provides critical information about how the gate electrode of a GaN HEMT, which has been identified as the most sensitive among GaN microsensors, needs to be designed, and what operation parameters should be used for high sensitivity detection.

  12. Stability of Carbon Incorpoated Semipolar GaN(1101) Surface

    Akiyama, Toru; Nakamura, Kohji; Ito, Tomonori


    The structural stability of carbon incorporated GaN(1101) surfaces is theoretically investigated by performing first-principles pseudopotential calculations. The calculated surface formation energies taking account of the metal organic vapor phase epitaxy conditions demonstrate that several carbon incorporated surfaces are stabilized depending on the growth conditions. Using surface phase diagrams, which are obtained by comparing the calculated adsorption energy with vapor-phase chemical potentials, we find that the semipolar surface forms NH2 and CH2 below ˜1660 K while the polar GaN(0001) surface with CH3 is stabilized below ˜1550 K. This difference could be one of possible explanations for p-type doping on the semipolar GaN(1101) surface.

  13. Ablation of GaN Using a Femtosecond Laser

    刘伟民; 朱荣毅; 钱土雄; 袁述; 张国义


    We study the pulsed laser ablation of wurtzite gallium nitride (GaN) films grown on sapphire, using the fem tosecond laser beam at a central wavelength of 800nm as the source for the high-speed ablation of GaN films. By measuring the backscattered Raman spectrum of ablated samples, the dependence of the ablation depth on laser fluence with one pulse was obtained. The threshold laser fluence for the ablation of GaN films was determined to be about 0.25J/cm2. Laser ablation depth increases with the increasing laser fluence until the amount of removed material is not further increased. The ablated surface was investigated by an optical surface interference profile meter.

  14. Studies on electronic structure of GaN(0001) surface

    Xie Chang Kun; Xu Fa Qiang; Deng Rui; Liu Feng; Yibulaxin, K


    An electronic structure investigation on GaN(0001) is reported. The authors employ a full-potential linearized augmented plane-wave (FPLAPW) approach to calculate the partial density of state, which is in agreement with previous experimental results. The effects of the Ga3d semi-core levels on the electronic structure of GaN are discussed. The valence-electronic structure of the wurtzite GaN(0001) surface is investigated using synchrotron radiation excited angle-resolved photoemission spectroscopy. The bulk bands dispersion along GAMMA A direction in the Brillouin zones is measured using normal-emission spectra by changing photon-energy. The band structure derived from authors' experimental data is compared well with the results of authors' FPLAPW calculation. Furthermore, off-normal emission spectra are also measured along the GAMMA K and GAMMA M directions. Two surface states are identified, and their dispersions are characterized

  15. Application of GaN for photoelectrolysis of water

    Puzyk, M. V.; Usikov, A. S.; Kurin, S. Yu; Puzyk, A. M.; Fomichev, A. D.; Ermakov, I. A.; Kovalev, D. S.; Papchenko, B. P.; Helava, H.; Makarov, Yu N.


    GaN layers of n-type and p-type conductivity grown by HVPE on sapphire substrates were used as working electrodes for water electrolysis, photoelectrolysis and hydrogen gas generation. Specifically the water splitting process is discussed. Corrosion of the GaN materials is also considered. The hydrogen production rate under 365-nm UV LED irradiation of the GaN and external bias was 0.3 ml/(cm2*h) for an n-GaN photoanode (n∼8×1016 cm-3) in 1M Na2SO4 electrolyte and 1.2 ml/(cm2*h) for an n-GaN photoanode (n∼1×1017 cm-3) in 1M KOH electrolyte.

  16. Magnesium doped GaN grown by MOCVD

    Guarneros, C., E-mail: [Ingenieria Electrica, Seccion Electronica del Estado Solido, Centro de Investigacion y de Estudios Avanzados del Instituto Politecnico Nacional, Av. I.P.N. 2508, San Pedro Zacatenco, 07360 Mexico, D.F. (Mexico); Sanchez, V. [Ingenieria Electrica, Seccion Electronica del Estado Solido, Centro de Investigacion y de Estudios Avanzados del Instituto Politecnico Nacional, Av. I.P.N. 2508, San Pedro Zacatenco, 07360 Mexico, D.F. (Mexico)


    We have studied the optical and electrical characteristics of undoped and doped GaN layers. The n- and p-type layers have been prepared by low pressure MOCVD technique. Photoluminescence (PL) studies were carried at low temperature. In the PL spectra of undoped GaN layer, a low intensity band edge emission and a broad yellow emission band were observed. The donor-acceptor pair (DAP) emission and its phonon replicas were observed in Mg lightly doped GaN layer. The dominance of the blue and the yellow emissions increased in the PL spectra as the Mg concentration was increased. The X-ray diffraction was employed to study the structure of the layers. Both the undoped and the doped layers exhibited hexagonal structure. The samples were annealed and significant changes were not observed in Hall Effect and in the PL measurements, so we suggest that there is no need of a thermal annealing for magnesium acceptor activation.

  17. Conductivity based on selective etch for GaN devices and applications thereof

    Zhang, Yu; Sun, Qian; Han, Jung


    This invention relates to methods of generating NP gallium nitride (GaN) across large areas (>1 cm.sup.2) with controlled pore diameters, pore density, and porosity. Also disclosed are methods of generating novel optoelectronic devices based on porous GaN. Additionally a layer transfer scheme to separate and create free-standing crystalline GaN thin layers is disclosed that enables a new device manufacturing paradigm involving substrate recycling. Other disclosed embodiments of this invention relate to fabrication of GaN based nanocrystals and the use of NP GaN electrodes for electrolysis, water splitting, or photosynthetic process applications.

  18. Critical issues for homoepitaxial GaN growth by molecular beam epitaxy on hydride vapor-phase epitaxy-grown GaN substrates

    Storm, D. F.; Hardy, M. T.; Katzer, D. S.; Nepal, N.; Downey, B. P.; Meyer, D. J.; McConkie, Thomas O.; Zhou, Lin; Smith, David J.


    While the heteroepitaxial growth of gallium nitride-based materials and devices on substrates such as SiC, sapphire, and Si has been well-documented, the lack of a cost-effective source of bulk GaN crystals has hindered similar progress on homoepitaxy. Nevertheless, freestanding GaN wafers are becoming more widely available, and there is great interest in growing GaN films and devices on bulk GaN substrates, in order to take advantage of the greatly reduced density of threading dislocations, particularly for vertical devices. However, homoepitaxial GaN growth is far from a trivial task due to the reactivity and different chemical sensitivities of N-polar (000_1) and Ga-polar (0001) GaN surfaces, which can affect the microstructure and concentrations of impurities in homoepitaxial GaN layers. In order to achieve high quality, high purity homoepitaxial GaN, it is necessary to investigate the effect of the ex situ wet chemical clean, the use of in situ cleaning procedures, the sensitivity of the GaN surface to thermal decomposition, and the effect of growth temperature. We review the current understanding of these issues with a focus on homoepitaxial growth of GaN by molecular beam epitaxy (MBE) on c-plane surfaces of freestanding GaN substrates grown by hydride vapor phase epitaxy (HVPE), as HVPE-grown substrates are most widely available. We demonstrate methods for obtaining homoepitaxial GaN layers by plasma-assisted MBE in which no additional threading dislocations are generated from the regrowth interface and impurity concentrations are greatly reduced.

  19. Highly transparent ammonothermal bulk GaN substrates

    Jiang, WK; Ehrentraut, D; Downey, BC; Kamber, DS; Pakalapati, RT; Do Yoo, H; D' Evelyn, MP


    A novel apparatus has been employed to grow ammonothermal (0001) gallium nitride (GaN) with diameters up to 2 in The crystals have been characterized by x-ray diffraction rocking-curve (XRC) analysis, optical and scanning electron microscopy (SEM), cathodoluminescence (CL), and optical spectroscopy. High crystallinity GaN with FWHM values about 20-50 arcsec and dislocation densities below 1 x 10(5) cm(-2) have been obtained. High optical transmission was achieved with an optical absorption coefficient below 1 cm(-1) at a wavelength of 450 nm. (C) 2014 Elsevier B.V. All rights reserved.

  20. Ferromagnetism in undoped One-dimensional GaN Nanowires

    K. Jeganathan


    Full Text Available We report an intrinsic ferromagnetism in vertical aligned GaN nanowires (NW fabricated by molecular beam epitaxy without any external catalyst. The magnetization saturates at ∼0.75 × emu/gm with the applied field of 3000 Oe for the NWs grown under the low-Gallium flux of 2.4 × 10−8 mbar. Despite a drop in saturation magnetization, narrow hysteresis loop remains intact regardless of Gallium flux. Magnetization in vertical standing GaN NWs is consistent with the spectral analysis of low-temperature photoluminescence pertaining to Ga-vacancies associated structural defects at the nanoscale.

  1. Chemical mechanical polishing of freestanding GaN substrates

    颜怀跃; 修向前; 刘战辉; 张荣; 华雪梅; 谢自力; 韩平; 施毅; 郑有炓


    Chemical mechanical polishing (CMP) has been used to produce smooth and scratch-free surfaces for GaN. In the aqueous solution of KOH, GaN is subjected to etching. At the same time, all surface irregularities, including etch pyramids, roughness after mechanical polishing and so on will be removed by a polishing pad. The experiments had been performed under the condition of different abrasive particle sizes of the polishing pad. Also the polishing results for different polishing times are analyzed, and chemical mechanical polishing resulted in an average root mean square (RMS) surface roughness of 0.565 nm, as measured by atomic force microscopy.

  2. Photoemission of graded-doping GaN photocathode

    Fu Xiao-Qian; Chang Ben-Kang; Wang Xiao-Hui; Li Biao; Du Yu-Jie; Zhang Jun-Ju


    We study the photoemission process of graded-doping GaN photocathode and find that the built-in electric fields can increase the escape probability and the effective diffusion length of photo-generated electrons, which results in the enhancement of quantum efficiency. The intervalley scattering mechanism and the lattice scattering mechanism in high electric fields are also investigated. To prevent negative differential mobility from appearing, the surface doping concentration needs to be optimized, and it is calculated to be 3.19×1017 cm-3. The graded-doping GaN photocathode with higher performance can be realized by further optimizing the doping profile.

  3. Ultra-high Efficiency DC-DC Converter using GaN Devices

    Ramachandran, Rakesh


    with the PCB layout and the magnetics. This thesis mainly covers the design and implementation of various high efficiency isolated dcdc converters in the range of 1 to 2.5 kW of output power. Both hard-switched and soft-switched topologies in isolated dc-dc converters has been studied and realized......The demands for high efficiency dc-dc power converters are increasing day by day in various applications such as telecommunication, data-centers, electric vehicles and various renewable energy systems. Silicon (Si) has been used as the semiconductor material in majority of the power devices...... for many decades. However, the rate of improvement slowed as the silicon power materials asymptotically approached its theoretical bounds. Compared to Si, wideband gap materials such as Silicon Carbide (SiC) and Gallium Nitride (GaN) are promising semiconductors for power devices due to their superior...

  4. MAY DAY



    @@ May 1 is Intemational Labour Day.It is a great holiday for the working class.On this day working people all over the world demonstrate(显示)their power and solidarity(团结).It has its origins(起因,起源)in the struggle for shorter working hours.In 1884,eight Labour Unions of the United States and Canada held a convention(集会)in Chicago(芝加哥).Here it was decided to wage(开展)a united struggle to win the eight-hour day.A resolution(决议) was adopted (通过)fixing May1,1886,for a great nationwide(全国性的)demonstration(示威).

  5. Growth of ZnO and GaN Films

    Chang, J.; Hong, S.-K.; Matsumoto, K.; Tokunaga, H.; Tachibana, A.; Lee, S. W.; Cho, M.-W.

    . Zinc oxide (ZnO) and gallium nitride (GaN) are wide bandgap semi conductors applicable to light emitting diodes (LEDs) and laser diodes (LDs) with wavelengths ranging from ultraviolet to blue light. Now ZnO and GaN are key ma terials for optoelectronic device applications and their applications are being rapidly expanded to lots of other technology including electronics, biotechnology, nanotech-nology, and fusion technology among all these. As a fundamental starting point for the development of this new technique, epitaxy of ZnO and GaN films is one of the most important key technology. Hence, development of the growth technique for high quality epitaxial films is highly necessary. Among the various kinds of epi taxy technique for semiconductor films developed so far, physical vapor deposition (PVD)-based epitaxy technique has been revealed to be the appropriate way for the high quality ZnO film and related alloy growths, while chemical vapor deposition (CVD)-based epitaxy technique has been proved to be the best method for the high quality GaN film and related alloy growths.

  6. Photoluminescence of Zn-implanted GaN

    Pankove, J. I.; Hutchby, J. A.


    The photoluminescence spectrum of Zn-implanted GaN peaks at 2.87 eV at room temperature. The emission efficiency decreases linearly with the logarithm of the Zn concentration in the range from 1 x 10 to the 18th to 20 x 10 to the 18th Zn/cu cm.

  7. Simulation of growing GaN in vertical HVPE reactor


    The paper reports the setting up of a model of fluid dynamic for GaN HVPE system and the simulation. It is found that when the direction of gravity is opposite to the direction of GaCl flow inlet,there exits a distance at which the uniformity of the deposition is optimal. Here the good uniformity of the deposition is obtained when the distance between the substrate and GaCl inlet is 5 cm. The parameters of gas flow used in growing GaN are also optimized. In addition, the influence of gravity and buoyancy on the deposition of GaN is discussed, too. It is found that the angle between the direction of gravity and the direction of GaCl flow inlet has a major effect on the deposition rate and the uniformity of the growth. Compared with the situation when the direction of gravity is the same with the direction of GaCl flow inlet, although the deposition rate of GaN has decreased obviously, the uniformity of the deposition has improved largely when the direction of gravity is opposite to the direction of GaCl flow inlet.

  8. Taevo Gans : särama pandud postmodernism / Kadi Viljak

    Viljak, Kadi


    Viking Window ASi büroo ja ekspositsioonisaal 1979. a. Jüri Okase projekteeritud endises Paide KEKi remontmehaanikatöökoja hoones Mäos. Sisearhitekt Taevo Gans, kelle projekteeritud on ka ettevõtte juhi töölaud. T. Gansi kommentaarid. Ill.: 6 värv. sisevaadet

  9. Radiation effects in GaN devices and materials (Conference Presentation)

    Sun, Ke-Xun; Nelson, Ron; Yeamans, Charles


    Gallium Nitride (GaN) is a wide-bandgap semiconductor having excellent radiation properties. GaN crystal is ionic-covalent with significant iconicity resulting in stronger molecular bond strength, which in in turn leads to excellent radiation hardness. Further, GaN has ultrafast carrier relaxation time. GaN transistors are promising for high-frequency applications due to their large bandgap (3.9eV) and higher breakdown field (NIF) high foot, high yield shots. In 2013 LANSCE run cycle, we tested GaN UV LED devices at 3.1E11 neutrons/cm^2. In 2015-2016 LANSCE run cycles, we have been operating three neutron beam lines with fluence level 1.2E11, 1.5E13, and 1E15 neutrons/cm^2. The irradiated samples include GaN UV LEDs, GaN HEMTs, and GaN substrates. In the experiments up to 2015 run cycle, we have characterized electrical and optical performances of GaN device before and after neutron irradiation, including the device IV curve measurements monitored at over the three months neutron irradiation time, and device IV curve measurements before and after NIF high yield shot irradiation. We observed no substantial degradation. These experiments firmly established GaN devices as the radiation hard platform of the next generation fusion plasma diagnostic instruments.

  10. GaN as a radiation hard particle detector

    Grant, J.; Bates, R.; Cunningham, W.; Blue, A.; Melone, J.; McEwan, F.; Vaitkus, J.; Gaubas, E.; O'Shea, V.


    Semiconductor tracking detectors at experiments such as ATLAS and LHCb at the CERN Large Hadron Collider (LHC) will be subjected to intense levels of radiation. The proposed machine upgrade, the Super-LHC (SLHC), to 10 times the initial luminosity of the LHC will require detectors that are ultra-radiation hard. Much of the current research into finding a detector that will meet the requirements of the SLHC has focused on using silicon substrates with enhanced levels of oxygen, for example Czochralski silicon and diffusion oxygenated float zone silicon, and into novel detector structures such as 3D devices. Another avenue currently being investigated is the use of wide band gap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN). Both SiC and GaN should be intrinsically more radiation hard than silicon. Pad and guard ring structures were fabricated on three epitaxial GaN wafers. The epitaxial GaN thickness was either 2.5 or 12 μm and the fabricated detectors were irradiated to various fluences with 24 GeV/c protons and 1 MeV neutrons. Detectors were characterised pre- and post-irradiation by performing current-voltage ( I- V) and charge collection efficiency (CCE) measurements. Devices fabricated on 12 μm epitaxial GaN irradiated to fluences of 1016 protons cm-2 and 1016 neutrons cm-2 show maximum CCE values of 26% and 20%, respectively, compared to a maximum CCE of 53% of the unirradiated device.

  11. Thanksgiving Day



    Fourth Thursday in November almost every culture in the world has held celebrations of thanks for a plentiful harvest.The American thanksgiving in the early days of the American colonies almost four hundred years ago.On that date in 1621,the European settlers in Plymouth,Massachusetts,gave their thanks to god for letting them survive their first year in the new world.They celebrated by having a large feast or dinner.

  12. May Day



    May Day is of course the traditional worldwide holiday for workers. Be sure, even though the market economy is by now the prevalent economic modus operandi in sodalist as well as capitalist countries, the workers movement has not lost a bit of its importance. The workers are those who keep the economy on track. And the workers are also the consumers, Without consumers, as every first term economy student at any university knows by now, there is no national economic growth. Therefore, the second long holiday of the year will certainly- be conducive to the economy.

  13. Growth of GaN micro/nanolaser arrays by chemical vapor deposition

    Liu, Haitao; Zhang, Hanlu; Dong, Lin; Zhang, Yingjiu; Pan, Caofeng


    Optically pumped ultraviolet lasing at room temperature based on GaN microwire arrays with Fabry-Perot cavities is demonstrated. GaN microwires have been grown perpendicularly on c-GaN/sapphire substrates through simple catalyst-free chemical vapor deposition. The GaN microwires are [0001] oriented single-crystal structures with hexagonal cross sections, each with a diameter of ˜1 μm and a length of ˜15 μm. A possible growth mechanism of the vertical GaN microwire arrays is proposed. Furthermore, we report room-temperature lasing in optically pumped GaN microwire arrays based on the Fabry-Perot cavity. Photoluminescence spectra exhibit lasing typically at 372 nm with an excitation threshold of 410 kW cm-2. The result indicates that these aligned GaN microwire arrays may offer promising prospects for ultraviolet-emitting micro/nanodevices.

  14. Structures, nanomechanics, and disintegration of single-walled GaN nanotubes: atomistic simulations

    Kang, Jeong Won; Hwang, Ho Jung; Song, Ki Oh; Choi, Won Young; Byun, Ki Ryang [Chung-Ang University, Seoul (Korea, Republic of); Kwon, Oh Keun [Semyung University, Jecheon (Korea, Republic of); Lee, Jun Ha [Sangmyung University, Chonan (Korea, Republic of); Kim, Won Woo [Juseong College, Cheongwon (Korea, Republic of)


    We have investigated the structural, mechanical, and thermal properties of single-walled GaN nanotubes by using atomistic simulations and a Tersoff-type potential. The Tersoff potential for GaN effectively describes the properties of GaN nanotubes. The nanomechanics of GaN nanotubes under tensile and compressive loadings have also been investigated, and Young's modulus has been calculated. The caloric curves of single-walled GaN nanotubes can be divided into three regions corresponding to nanotubes, the disintegrating range, and vapor. Since the stability or the stiffness of a tube decreases with increasing curving sheet-to-tube strain energy, the disintegration temperatures of GaN nanotubes are closely related to the curving sheet-to-tube strain energy.

  15. Study of radiation detection properties of GaN pn diode

    Sugiura, Mutsuhito; Kushimoto, Maki; Mitsunari, Tadashi; Yamashita, Kohei; Honda, Yoshio; Amano, Hiroshi; Inoue, Yoku; Mimura, Hidenori; Aoki, Toru; Nakano, Takayuki


    Recently, GaN, which has remarkable properties as a material for optical devices and high-power electron devices, has also attracted attention as a material for radiation detectors. We previously suggested the use of BGaN as a neutron detector material. However, the radiation detection characteristics of GaN itself are not yet adequately understood. For realizing a BGaN neutron detector, the understanding of the radiation detection characteristics of GaN, which is a base material of the neutron detector, is important. In this study, we evaluated the radiation detection characteristics of GaN. We performed I-V and energy spectrum measurements under alpha ray, gamma ray, and thermal neutron irradiations to characterize the radiation detection characteristics of a GaN diode. The obtained results indicate that GaN is an effective material for our proposed new BGaN-based neutron detector.

  16. Gadolinium-Based GaN for Neutron Detection with Gamma Discrimination


    from evaluating these detectors are summarized as, 1) semi-insulating GaN [1] does not show radiation response due to the high density carrier...Praneeth Kandlakunta, 2012 2) “ Evaluation of GaN as a Radiation Detection Material “, Jinghui Wang, 2012 Journal Articles: 1) P. Kandlakunta... Evaluation of GaN as a Radiation Detection Material. Thesis,The Ohio State University, 2012. 8. Kandlakunta, P., Gamma Rays Rejection in a Gadolinium based

  17. Fully Coupled Thermoelectromechanical Analysis of GaN High Electron Mobility Transistor Degradation


    multi-dimensional continuum model of the thermoelectromechanics of GaN HEMTs is presented and discussed. The governing equations are those of linear...understanding the mechanisms of both electrical and mechanical degradation in GaN HEMTs . Various possible contributors to degradation are discussed...layers in conventional GaN HEMTs , there is another limit, observed following sustained operation at high current/voltage levels, wherein highly

  18. Preparation and properties of GaN films on Si(111) substrates

    杨莺歌; 马洪磊; 郝晓涛; 马瑾; 薛成山; 庄惠照


    High-quality gallium nitride (GaN) films were prepared on Si(111) substrates by sputtering post-annealing-reaction technique. XRD, XPS, and SEM measurement results indicate that polycrystalline GaN with hexagonal structure was successfully prepared. Intense room- temperature photoluminescence that peaked at 354 nm of the films is observed. The bandgap of these films has a blueshift with respect to bulk GaN.

  19. Thermal Annealing induced relaxation of compressive strain in porous GaN structures

    Ben Slimane, Ahmed


    The effect of annealing on strain relaxation in porous GaN fabricated using electroless chemical etching is presented. The Raman shift of 1 cm-1 in phonon frequency of annealed porous GaN with respect to as-grown GaN corresponds to a relaxation of compressive strain by 0.41 ± 0.04 GPa. The strain relief promises a marked reduction in threading dislocation for subsequent epitaxial growth.

  20. Formation of Amine Groups on the Surface of GaN: A Method for Direct Biofunctionalization


    the formation of surface sensitive GaN /AlGaN two- dimensional electron gas HEMT devices [5–14]. Furthermore, GaN is robust in aqueous solutions [15...variations are particularly detrimental to GaN HEMT sensors, as they are highly sensitive to the separation between the target and the device surface. Because...locate /apsuscFormation of amine groups on the surface of GaN : A method for direct biofunctionalization R. Stine, B.S. Simpkins, S.P. Mulvaney, L.J

  1. High surface hole concentration p-type GaN using Mg implantation

    Long Tao; Zhang Guo Yi


    Mg ions were implanted on Mg-doped GaN grown by metalorganic chemical vapor deposition (MOCVD). The p-type GaN was achieved with high hole concentration (8.28 x 10 sup 1 sup 7 cm sup - sup 3) conformed by Van derpauw Hall measurement after annealing at 800 degree C for 1 h. this is the first experimental report of Mg implantation on Mg-doped GaN and achieving p-type GaN with high surface hole concentration

  2. Demonstration of flexible thin film transistors with GaN channels

    Bolat, S.; Sisman, Z.; Okyay, A. K.


    We report on the thin film transistors (TFTs) with Gallium Nitride (GaN) channels directly fabricated on flexible substrates. GaN thin films are grown by hollow cathode plasma assisted atomic layer deposition (HCPA-ALD) at 200 °C. TFTs exhibit 103 on-to-off current ratios and are shown to exhibit proper transistor saturation behavior in their output characteristics. Gate bias stress tests reveal that flexible GaN TFTs have extremely stable electrical characteristics. Overall fabrication thermal budget is below 200 °C, the lowest reported for the GaN based transistors so far.

  3. Spontaneous nucleation and growth of GaN nanowires: the fundamental role of crystal polarity.

    Fernández-Garrido, Sergio; Kong, Xiang; Gotschke, Tobias; Calarco, Raffaella; Geelhaar, Lutz; Trampert, Achim; Brandt, Oliver


    We experimentally investigate whether crystal polarity affects the growth of GaN nanowires in plasma-assisted molecular beam epitaxy and whether their formation has to be induced by defects. For this purpose, we prepare smooth and coherently strained AlN layers on 6H-SiC(0001) and SiC(0001̅) substrates to ensure a well-defined polarity and an absence of structural and morphological defects. On N-polar AlN, a homogeneous and dense N-polar GaN nanowire array forms, evidencing that GaN nanowires form spontaneously in the absence of defects. On Al-polar AlN, we do not observe the formation of Ga-polar GaN NWs. Instead, sparse N-polar GaN nanowires grow embedded in a Ga-polar GaN layer. These N-polar GaN nanowires are shown to be accidental in that the necessary polarity inversion is induced by the formation of Si(x)N. The present findings thus demonstrate that spontaneously formed GaN nanowires are irrevocably N-polar. Due to the strong impact of the polarity on the properties of GaN-based devices, these results are not only essential to understand the spontaneous formation of GaN nanowires but also of high technological relevance.

  4. Fabrication of Syringe-Shaped GaN Nanorods

    XUE Cheng-Shan; CAO Yu-Ping; WU Yu-Xin; ZHUANG Hui-Zhao; TIAN De-Heng; LIU Yi-An; HE Jian-Ting; AI Yu-Jie; SUN Li-Li; WANG Fu-Xue


    @@ Syringe-shaped GaN nanorods are synthesized on Si(111) substrates by annealing sputtered Ga2O3/BN films under flowing ammonia at temperature of 950° C. Most of the nanorods consist of a main rod and a top needle, looking like a syringe. X-ray diffraction and selected-area electron diffraction confirm that the syringe-shaped nanorods are hexagonal wurtzite GaN. Scanning electron microscopy and high-resolution transmission electron microscopy reveal that these nanorods are as long as several micrometres, with diameters ranging from 100 to 300 nm. In addition to the BN intermediate layer, the proper annealing temperature has been demonstrated to be a crucial factor for the growth of syringe-shaped nanorods by this method.

  5. ITON Schottky contacts for GaN based UV photodetectors

    Vanhove, N.; John, J.; Lorenz, A.; Cheng, K.; Borghs, G.; Haverkort, J. E. M.


    Lateral Schottky ultraviolet detectors were fabricated in GaN using indium-tin-oxynitride (ITON) as a contact metal. The GaN semiconductor material was grown on 2 in. sapphire substrate by metal-organic chemical vapor deposition (MOCVD). The Schottky contact has been realized using ITON that has been deposited using sputter techniques. I- V characteristics have been measured with and without UV illumination. The device shows photo-to-dark current ratios of 10 3 at -1 V bias. The spectral responsivity of the UV detectors has been determined. The high spectral responsivity of more than 30 A/W at 240 nm is explained by a high internal gain caused by generation-recombination centers at the ITON/GaN interface. Persistent photocurrent effect has been observed in UV light (on-off) switching operation, time constant and electron capture coefficient of the transition has been determined.

  6. Indirect interband transition in hexagonal GaN

    Lancry, O; Pichonat, E [Laboratoire de Spectrochimie Infrarouge et Raman (LASIR), UMR CNRS 8516, Universite des Sciences et Technologies de Lille, bat C5, 59655 Villeneuve d' Ascq cedex (France); Farvacque, J-L [Unite Materiaux et Transformations (UMET), UMR CNRS 8207, Universite des Sciences et Technologies de Lille, bat C6, 59655 Villeneuve d' Ascq cedex (France); Gaquiere, C, E-mail: [Institut d' Electronique de Microelectronique et de Nanotechnologie (IEMN), UMR CNRS 8520, Cite Scientifique, Avenue Poincare, BP 60069, 59652 Villeneuve d' Ascq cedex (France)


    In this paper, we report on optical investigations with Raman experiment to underline a new ultraviolet (UV) luminescence band in hexagonal gallium nitride (GaN) at 4.56 eV. GaN is a direct band gap semiconductor, the photoluminescence peak corresponding to the energy gap at 3.43 eV dominates the spectrum. Nevertheless, other electronic interband transitions can appear on the spectrum: the electronic indirect interband transitions. We attribute one of them to the observed new photoluminescence band at 4.56 eV. This interpretation is supported by photoluminescence spectra obtained on three different samples at room temperature and at -50 deg. C with UV excitation source: mbd-266 nm solid laser (4.66 eV) and by the study of three criteria: the partly opposite parities of initial and final wave function, the implication of acoustic phonons and temperature control.

  7. Step bunching on the vicinal GaN(0001) surface

    Ramana Murty, M. V.; Fini, P.; Stephenson, G. B.; Thompson, Carol; Eastman, J. A.; Munkholm, A.; Auciello, O.; Jothilingam, R.; DenBaars, S. P.; Speck, J. S.


    Nominally 2{sup o} vicinal GaN(0001) surfaces exhibit monolayer-height steps at 990{sup o}C in the metal-organic chemical vapor deposition environment. Real-time x-ray scattering observations at 715--990{sup o}C indicate that there is a tendency for step bunching during growth. Below 850{sup o}C, step bunches nucleated during growth remain and coarsen after growth, while above 850{sup o}C, the surface reverts to monolayer-height steps after growth. Surfaces vicinal toward the {l_brace}1{bar 1}00{r_brace} and the {l_brace}11{bar 2}0{r_brace} planes exhibit similar behavior. We suggest a simple equilibrium surface orientational phase diagram for vicinal GaN(0001) that is consistent with these observations.

  8. Study of Charge Carrier Transport in GaN Sensors

    Eugenijus Gaubas


    Full Text Available Capacitor and Schottky diode sensors were fabricated on GaN material grown by hydride vapor phase epitaxy and metal-organic chemical vapor deposition techniques using plasma etching and metal deposition. The operational characteristics of these devices have been investigated by profiling current transients and by comparing the experimental regimes of the perpendicular and parallel injection of excess carrier domains. Profiling of the carrier injection location allows for the separation of the bipolar and the monopolar charge drift components. Carrier mobility values attributed to the hydride vapor phase epitaxy (HVPE GaN material have been estimated as μe = 1000 ± 200 cm2/Vs for electrons, and μh = 400 ± 80 cm2/Vs for holes, respectively. Current transients under injection of the localized and bulk packets of excess carriers have been examined in order to determine the surface charge formation and polarization effects.

  9. Study of Charge Carrier Transport in GaN Sensors.

    Gaubas, Eugenijus; Ceponis, Tomas; Kuokstis, Edmundas; Meskauskaite, Dovile; Pavlov, Jevgenij; Reklaitis, Ignas


    Capacitor and Schottky diode sensors were fabricated on GaN material grown by hydride vapor phase epitaxy and metal-organic chemical vapor deposition techniques using plasma etching and metal deposition. The operational characteristics of these devices have been investigated by profiling current transients and by comparing the experimental regimes of the perpendicular and parallel injection of excess carrier domains. Profiling of the carrier injection location allows for the separation of the bipolar and the monopolar charge drift components. Carrier mobility values attributed to the hydride vapor phase epitaxy (HVPE) GaN material have been estimated as μe = 1000 ± 200 cm²/Vs for electrons, and μh = 400 ± 80 cm²/Vs for holes, respectively. Current transients under injection of the localized and bulk packets of excess carriers have been examined in order to determine the surface charge formation and polarization effects.

  10. Optical properties of Yb ions in GaN epilayer

    Jadwisienczak, W. M.; Lozykowski, H. J.


    In recent years, an important effort in semiconductor materials research has been devoted to III-nitrides semiconductors doped with rare earth ions due to the high potential of these materials in light-emitting device applications. Ytterbium (Yb 3+) is one of a few lanthanide ions which have not been investigated as an optically active center in these materials yet. In this paper we report the observation of luminescence from GaN films grown on sapphire (0 0 0 1) substrate by metal organic chemical vapor deposition and doped by implantation with Yb 3+ ions. The high resolution photo- and cathodoluminescence spectra of GaN:Yb 3+ were studied at different excitation conditions in temperatures ranging from 8 to 330 K and revealed weak thermal quenching. The luminescence emission lines are assigned to transitions between the spin-orbit levels 2F 5/2 → 2F 7/2 of Yb 3+ (4f 13). The analysis of the Yb luminescence spectra allowed us to suggest the energy level diagram of the crystal-field-split 4f 13 levels for the Yb ion center. The most probable lattice location of Yb in GaN is the substitutional Ga site. Furthermore, the luminescence kinetics of internal transitions of Yb 3+ incorporated in GaN was investigated by means of decay and time-resolved luminescence measurements. It was found that the ytterbium decay is non-exponential with dominant exponential term of ˜100 μs with little dependence on the ambient temperature. The results indicate that Yb-doped GaN epilayer may be suitable as a material for near infrared optoelectronic devices.

  11. Temperature Dependence of GaN HEMT Small Signal Parameters

    Ali M. Darwish


    Full Text Available This study presents the temperature dependence of small signal parameters of GaN/SiC HEMTs across the 0–150°C range. The changes with temperature for transconductance (m, output impedance (ds and ds, feedback capacitance (dg, input capacitance (gs, and gate resistance (g are measured. The variations with temperature are established for m, ds, ds, dg, gs, and g in the GaN technology. This information is useful for MMIC designs.

  12. Photoluminescence of ion-implanted GaN

    Pankove, J. I.; Hutchby, J. A.


    Thirty-five elements were implanted in GaN. Their photoluminescence spectra were measured and compared to those of an unimplanted control sample. Most impurities emit a peak at about 2.15 eV. Mg, Zn, Cd, Ca, As, Hg, and Ag have more characteristic emissions. Zn provides the most efficient recombination center. A set of midgap states is generated during the damage-annealing treatment.

  13. Room Temperature Ultralow Threshold GaN Nanowire Polariton Laser

    Das, Ayan


    We report ultralow threshold polariton lasing from a single GaN nanowire strongly coupled to a large-area dielectric microcavity. The threshold carrier density is 3 orders of magnitude lower than that of photon lasing observed in the same device, and 2 orders of magnitude lower than any existing room-temperature polariton devices. Spectral, polarization, and coherence properties of the emission were measured to confirm polariton lasing. © 2011 American Physical Society.

  14. Model for radiation damage buildup in GaN

    Titov, A.I. [State Polytechnic University, St. Petersburg 195251 (Russian Federation); Karaseov, P.A., E-mail: [State Polytechnic University, St. Petersburg 195251 (Russian Federation); Kataev, A.Yu. [State Polytechnic University, St. Petersburg 195251 (Russian Federation); Azarov, A.Yu. [Department of Physics, University of Oslo, P.O. Box 1048, Blindern, Oslo NO-0316 (Norway); Kucheyev, S.O. [Lawrence Livermore National Laboratory, Livermore, CA 94551 (United States)


    We propose a model that explains both saturation and a shift of the maximum of bulk disorder profiles in ion-implanted GaN. Our model is based on two main assumptions that (i) the advancing amorphous/crystalline interface acts as a perfect sink for mobile point defects generated in the crystal bulk and (ii) the diffusion length of mobile defects increases with increasing ion fluence due to saturation of defect sinks in the bulk.

  15. Voltage controlled terahertz transmission through GaN quantum wells

    Laurent, T.; Sharma, R.; Torres, J.; Nouvel, P; Blin, S.; Varani, L.; Cordier, Y.; Chmielowska, M.; Chenot, S.; Faurie, JP; Beaumont, B.; P. Shiktorov; Starikov, E.; Gruzinskis, V.; Korotyevyev, V.


    We report measurements of radiation transmission in the 0.220--0.325 THz frequency domain through GaN quantum wells grown on sapphire substrates at room and low temperatures. A significant enhancement of the transmitted beam intensity with the applied voltage on the devices under test is found. For a deeper understanding of the physical phenomena involved, these results are compared with a phenomenological theory of light transmission under electric bias relating the transmission enhancement ...

  16. Metal contacts on ZnSe and GaN

    Duxstad, K J [Univ. of California, Berkeley, CA (United States). Materials Science and Mineral Engineering


    Recently, considerable interest has been focused on the development of blue light emitting materials and devices. The focus has been on GaN and ZnSe, direct band gap semiconductors with bands gaps of 3.4 and 2.6 eV, respectively. To have efficient, reliable devices it is necessary to have thermally and electrically stable Ohmic contacts. This requires knowledge of the metal-semiconductor reaction behavior. To date few studies have investigated this behavior. Much information has accumulated over the years on the behavior of metals on Si and GaAs. This thesis provides new knowledge for the more ionic wide band gap semiconductors. The initial reaction temperatures, first phases formed, and phase stability of Pt, Pd, and Ni on both semiconductors were investigated. The reactions of these metals on ZnSe and GaN are discussed in detail and correlated with predicted behavior. In addition, comparisons are made between these highly ionic semiconductors and Si and GaAs. The trends observed here should also be applicable to other II-VI and III-Nitride semiconductor systems, while the information on phase formation and stability should be useful in the development of contacts for ZnSe and GaN devices.

  17. Rare earth point defects in GaN

    Sanna, S.


    In this work we investigate rare earth doped GaN, by means of theoretical simulations. The huge unit cells necessary to model the experimental system, where dilute amount of rare earth ions are used, are handled with the charge self consistent density-functional based-tight binding (SCC-DFTB) calculational scheme. The method has been extended to include LDA+U and simplified self interaction corrected (SIC)-like potentials for the simulation of systems with localised and strongly correlated electrons. A set of tight-binding parameters has been created to model the interaction of GaN with some dopants, including a selection of lanthanide ions interesting due to their optical or magnetic properties (Pr, Eu, Gd, Er and Tm). The f-electrons were treated as valence electrons. A qualitatively correct description of the band gap is crucial for the simulation of rare earth doped GaN, because the luminescence intensity of the implanted samples depends on the size of the host band gap and because the rare earths could introduce charge transition levels near the conduction band. In this work these levels are calculated with the Slater-Janak (SJ) transition state model, which allows an approximate calculation of the charge transition levels by analysing the Kohn-Sham eigenvalues of the DFT. (orig.)

  18. Annealing of GaN under high pressure of nitrogen

    Porowski, S; Kolesnikov, D; Lojkowski, W; Jager, V; Jäger, W; Bogdanov, V; Suski, T; Krukowski, S


    Gallium nitride, aluminum nitride and indium nitride are basic materials for blue optoelectronic devices. The essential part of the technology of these devices is annealing at high temperatures. Thermodynamic properties of the Ga-N system and their consequences to application of high nitrogen pressure for the annealing of GaN based materials are summarized. The diffusion of Zn, Mg and Au in high dislocation density heteroepitaxial GaN/Al sub 2 O sub 3 layers will be compared with the diffusion in dislocation-free GaN single crystals and homoepitaxial layers. It will be shown that high dislocation density can drastically change the diffusion rates, which strongly affects the performance of nitride devices. Inter-diffusion of Al, Ga and In in AlGaN/GaN and InGaN/GaN quantum well (QW) structures will be also considered. It will be shown that in contrast to stability of metal contacts, which is strongly influenced by dislocations, the inter-diffusion of group III atoms in QW structures is not affected strongly by...

  19. Study of neutron irradiated structures of ammonothermal GaN

    Gaubas, E.; Ceponis, T.; Deveikis, L.; Meskauskaite, D.; Miasojedovas, S.; Mickevicius, J.; Pavlov, J.; Pukas, K.; Vaitkus, J.; Velicka, M.; Zajac, M.; Kucharski, R.


    Study of the radiation damage in GaN-based materials becomes an important aspect for possible application of the GaN detectors in the harsh radiation environment at the Large Hadron Collider and at other particle acceleration facilities. Intentionally doped and semi-insulating bulk ammonothermal GaN materials were studied to reveal the dominant defects introduced by reactor neutron irradiations. These radiation defects have been identified by combining electron spin resonance and transmission spectroscopy techniques. Characteristics of carrier lifetime dependence on neutron irradiation fluence were examined. Variations of the response of the capacitor-type sensors with neutron irradiation fluence have been correlated with the carrier lifetime changes. The measurements of the photoconductivity and photoluminescence transients have been used to study the variation of the parameters of radiative and non-radiative recombination. The examined characteristics indicate that AT GaN as a particle sensing material is radiation hard up to high hadron fluences  ⩾1016 cm‑2.

  20. Abnormal selective area growth of irregularly-shaped GaN structures on the apex of GaN pyramids and its application for wide spectral emission

    Yu, Yeon Su; Lee, Jun Hyeong; Ahn, Hyung Soo; Yang, Min


    We report on the growth and the characterization of three-dimensional randomly-shaped InGaN/GaN structures selectively grown on the apex of GaN pyramids for the purpose of enlarging the emission spectral range. We found that the variations in the shape and the size of the three-dimensional GaN structures depend on the growth temperature and the surface area for selective growth under intentional turbulence in the gas stream. The selectively grown GaN structures grown at 1020 °C have irregular shape, while the samples grown at 1100 °C have rather uniform hexagonal pyramidal shapes. Irregularly shaped GaN structures were also obtained on the apex of GaN pyramids when the SiO2 mask was removed to 1/10 of the total height of the underlying GaN pyramid. When only 1/5 of the SiO2 mask was removed, however, the selectively grown GaN structures had similar hexagonal pyramidal shapes resembling those of the underlying GaN pyramids. The CL (Cathodoluminescence) spectra of the InGaN layers grown on the randomly shaped GaN structures showed a wide emission spectral range from 388 to 433 nm due to the non-uniform thickness and spatially inhomogeneous indium composition of the InGaN layers. This new selective growth method might have great potential for applications of non-phosphor white light emitting diodes (LEDs) with optimized growth conditions for InGaN active layers of high indium composition and with optimum process for fabrication of electrodes for electrical injection.

  1. Fabrication of GaN structures with embedded network of voids using pillar patterned GaN templates

    Svensk, O.; Ali, M.; Riuttanen, L.; Törmä, P. T.; Sintonen, S.; Suihkonen, S.; Sopanen, M.; Lipsanen, H.


    In this paper we report on the MOCVD growth and characterization of GaN structures and InGaN single quantum wells grown on pillar patterned GaN/sapphire templates. During the regrowth a network of voids was intentionally formed at the interface of sapphire substrate and GaN epitaxial layer. The regrowth process was found to decrease the threading dislocation density of the overgrown layer. The quantum well sample grown on patterned template showed significantly higher optical output in photoluminescence measurements compared to the reference sample with identical internal quantum efficiency characteristics. We attribute the increase to enhanced light extraction efficiency caused by strong scattering and redirection of light from the scattering elements.

  2. Multi-wavelength emitting InGan/GaN quantum well grown on V-shaped gan(1101) microfacet.

    Kang, Eun-Sil; Ju, Jin-Woo; Kim, Jin Soo; Ahn, Haeng-Keun; Lee, June Key; Kim, Jin Hyeok; Shin, Dong-Chan; Lee, In-Hwan


    InGaN/GaN multiple quantum wells (MQWs) were successfully grown on the inclined GaN(1101) microfacets. Conventional photolithography and subsequent growth of GaN were employed to generate the V-shaped microfacets along (1120) direction. The well-developed microfacets observed by scanning electron microscopy and the clear transmission electron microscope interfacial images indicated that the MQW was successfully grown on the GaN microfacets. Interestingly, cathodoluminescence (CL) spectra measured on the microfacets showed a continuous change in the luminescence peak positions. The CL peaks were shifted to a longer wavelength from 420 nm to 440 nm as the probing points were changed along upward direction. This could be attributed to the nonuniform distribution of the In composition and/or the wavefunction overlapping between adjacent wells. Present works thus propose a novel route to fabricate a monolithic white light emitting diode without phosphors by growing the InGaN/GaN MQWs on (1101) facet.

  3. Theoretical study of Structural and analytical potential energy functions of GaN


    Using Density Function Theory,the present work has optimized the equilibrium geometry of GaN. Murrell-Sorbie analytical potential energy functions of GaN have been derived by using ab initio data and the least-square fitting method,and harmonic frequency,force constant and spectroscopic data also have been calculated.

  4. Luminescence evolution of porous GaN thin films prepared via UV-assisted electrochemical etching

    Cheah, S.F., E-mail: [Nano-Optoelectronic Research and Technology Laboratory, School of Physics, Universiti Sains Malaysia, 11800 Penang (Malaysia); Lee, S.C. [Nano-Optoelectronic Research and Technology Laboratory, School of Physics, Universiti Sains Malaysia, 11800 Penang (Malaysia); Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ng, S.S.; Yam, F.K.; Abu Hassan, H.; Hassan, Z. [Nano-Optoelectronic Research and Technology Laboratory, School of Physics, Universiti Sains Malaysia, 11800 Penang (Malaysia)


    Porous gallium nitride (GaN) thin films with different surface morphologies and free carriers properties were fabricated from Si-doped GaN thin films using ultra-violet assisted electrochemical etching approach under various etching voltages. Fluctuation of luminescence signals was observed in the photoluminescence spectra of porous GaN thin films. Taking advantage of the spectral sensitivity of infrared attenuated total reflection spectroscopy on semiconductor materials, roles of free carriers and porous structure in controlling luminescence properties of GaN were investigated thoroughly. The results revealed that enhancement in luminescence signal is not always attained upon porosification. Although porosification is correlated to the luminescence enhancement, however, free carrier is the primary factor to enhance luminescence intensity. Due to unavoidable significant reduction of free carriers from Si-doped GaN in the porosification process, control of etching depth (i.e., thickness of porous layer formed from the Si-doped layer) is critical in fabricating porous GaN thin film with enhanced luminescence response. - Highlights: • Various pore morphologies with free carrier properties are produced by Si-doped GaN. • Free carriers are important to control the luminescence signal of porous GaN. • Enhancement of luminescence signal relies on the pore depth of Si-doped layer.

  5. Transmission measurement of the photonic band gap of GaN photonic crystal slabs

    Caro, J.; Roeling, E.M.; Rong, B.; Nguyen, H.M.; Van der Drift, E.W.J.M.; Rogge, S.; Karouta, F.; Van der Heijden, R.W.; Salemink, H.W.M.


    A high-contrast-ratio (30 dB) photonic band gap in the near-infrared transmission of hole-type GaN two-dimensional photonic crystals (PhCs) is reported. These crystals are deeply etched in a 650 nm thick GaN layer grown on sapphire. A comparison of the measured spectrum with finite difference time d

  6. Conduction, reverse conduction and switching characteristics of GaN E-HEMT

    Sørensen, Charlie; Lindblad Fogsgaard, Martin; Christiansen, Michael Noe;


    In this paper switching and conduction characterization of the GS66508P-E03 650V enhancement mode gallium nitride (GaN) transistor is described. GaN transistors are leading edge technology and as so, their characteristics are less than well documented. The switching characteristics are found using...

  7. Viability and proliferation of endothelial cells upon exposure to GaN nanoparticles

    Tudor Braniste


    Full Text Available Nanotechnology is a rapidly growing and promising field of interest in medicine; however, nanoparticle–cell interactions are not yet fully understood. The goal of this work was to examine the interaction between endothelial cells and gallium nitride (GaN semiconductor nanoparticles. Cellular viability, adhesion, proliferation, and uptake of nanoparticles by endothelial cells were investigated. The effect of free GaN nanoparticles versus the effect of growing endothelial cells on GaN functionalized surfaces was examined. To functionalize surfaces with GaN, GaN nanoparticles were synthesized on a sacrificial layer of zinc oxide (ZnO nanoparticles using hydride vapor phase epitaxy. The uptake of GaN nanoparticles by porcine endothelial cells was strongly dependent upon whether they were fixed to the substrate surface or free floating in the medium. The endothelial cells grown on surfaces functionalized with GaN nanoparticles demonstrated excellent adhesion and proliferation, suggesting good biocompatibility of the nanostructured GaN.

  8. High-pressure X-ray diffraction study of bulk- and nanocrystalline GaN

    Jorgensen, J.E.; Jakobsen, J.M.; Jiang, Jianzhong


    Bulk- and nanocrystalline GaN have been studied by high-pressure energy-dispersive X-ray diffraction. Pressure-induced structural phase transitions from the wurtzite to the NaCl phase were observed in both materials. The transition pressure was found to be 40 GPa for the bulk-crystalline GaN, while...

  9. Terahertz study of m-plane GaN thin fims

    Quadir, Shaham; Jang, Der-Jun; Lin, Ching-Liang; Lo, Ikai


    We investigate the optical properties of m-plane GaN thin films using the terahertz time domain spectroscopy. The m-plane GaN thin films were grown on γ-LiAlO2 substrates with buffer layers of low temperature grown GaN. The thin films were illuminated with terahertz radiation generated by a LT-GaAs antenna and the transmitted signal was detected by a ZnTe crystal. The polarization of the terahertz wave was chosen to be either parallel or perpendicular to the GaN [0001] direction. We compared the transmitted signals of the m-plane GaN thin films to that of the LAO substrate. The samples as well as the LAO substrate exhibited polarization dependence of absorption in terahertz spectrum. The carrier densities and the mobilities were derived from the transmittance of the THz wave using extended Drude model. We found, in all samples, both the carrier densities and mobilities along the GaN [0001] direction were smaller than those along the GaN [1120] direction due to the stripe formation along the GaN [1120].

  10. Vertical nonpolar growth templates for light emitting diodes formed with GaN nanosheets

    Yeh, Ting-Wei; Lin, Yen-Ting; Ahn, Byungmin; Stewart, Lawrence S.; Daniel Dapkus, P.; Nutt, Steven R.


    We demonstrate that nonpolar m-plane surfaces can be generated on uniform GaN nanosheet arrays grown vertically from the (0001)-GaN bulk material. InGaN/GaN multiple quantum wells (MQWs) grown on the facets of these nanosheets are demonstrated by cross-sectional transmission electron microscopy. Owing to the high aspect ratio of the GaN nanosheet structure, the MQWs predominantly grow on nonpolar GaN planes. The results suggest that GaN nanosheets provide a conduction path for device fabrication and also a growth template to reduce the piezoelectric field inside the active region of InGaN-based light emitting diodes.

  11. Evaluation of subsurface damage in GaN substrate induced by mechanical polishing with diamond abrasives

    Aida, Hideo, E-mail: [NJC Institute of Technology, Namiki Precision Jewel Co., Ltd., 3-8-22 Shinden, Adachi, Tokyo 123-8511 (Japan); KASTEC, Kyushu University, Kasuga-shi, Fukuoka 816-8580 (Japan); Takeda, Hidetoshi; Kim, Seong-Woo; Aota, Natsuko; Koyama, Koji [NJC Institute of Technology, Namiki Precision Jewel Co., Ltd., 3-8-22 Shinden, Adachi, Tokyo 123-8511 (Japan); Yamazaki, Tsutomu; Doi, Toshiro [KASTEC, Kyushu University, Kasuga-shi, Fukuoka 816-8580 (Japan)


    The relationship between the depth of the subsurface damage (SSD) and the size of the diamond abrasive used for mechanical polishing (MP) of GaN substrates was investigated in detail. GaN is categorized as a hard, brittle material, and material removal in MP proceeds principally to the fracture of GaN crystals. Atomic force microscopy and cathodoluminescence imaging revealed that the mechanical processing generated surface scratches and SSD. The SSD depth reduced as the diamond abrasive size reduced. A comparison of the relationship between the SSD depth and the diamond abrasive size used in the MP of GaN with the same relationship for typical brittle materials such as glass substrates suggests that the MP of GaN substrates proceeds via the same mechanism as glass.

  12. Frequency response and design consideration of GaN SAM avalanche photodiodes

    Xie, Feng; Yang, Guofeng; Zhou, Dong; Lu, Hai; Wang, Guosheng


    In this work, a method is developed for estimating the frequency response characteristics of GaN avalanche photodiodes (APDs) with separated absorption and multiplication regions (SAM). The method calculates the total diode current with varying frequency by solving transport equations analytically and uses a commercial device simulator as a supplement for determining the exact electrical field profile within the device. Due to the high carrier saturation velocity of GaN, a high-gain-bandwidth product over THz is found achievable for GaN SAM-APDs. The potential performances of GaN SAM-APDs with different structural designs are further compared through numerical studies. It is found that a close-to-reach-through design is attractive for simultaneously achieving both relatively low operation voltage and high working frequency. In addition, transit-time limit and RC-delay limit for the frequency response of GaN SAM-APDs are also discussed.

  13. Surface decomposition and annealing behavior of GaN implanted with Eu

    Liu Hua Ming; Chen Chang Chun; Wang Sen; Zhu De Zhang; Xu Hong Jie


    Investigations on surface decomposition of GaN implanted with low energy (80 keV) Eu ion to a low dose (1 x 10 sup 1 sup 4 cm sup - sup 2), and its annealing behavior under high temperature (1050 degree C) in N sub 2 are performed. The as-grown, as-implanted and annealed GaN films are characterized by proton elastic scattering (PES), Rutherford backscattering spectrometry (RBS), photoluminescence (PL) and atomic force microscopy (AFM). The results show that Eu ion implantation induces radiation defects and decomposition of GaN. The GaN surface decomposition is more serious during high temperature annealing. The atomic ratio of N in as-grown, as-implanted and annealed GaN film is 47 at.%, 44 at.% and 40 at.%, respectively. As a result, a rough Ga-rich layer is formed at the surface, though the lattice defects are partly removed after high temperature annealing

  14. Lattice-Symmetry-Driven Epitaxy of Hierarchical GaN Nanotripods

    Wang, Ping


    Lattice-symmetry-driven epitaxy of hierarchical GaN nanotripods is demonstrated. The nanotripods emerge on the top of hexagonal GaN nanowires, which are selectively grown on pillar-patterned GaN templates using molecular beam epitaxy. High-resolution transmission electron microscopy confirms that two kinds of lattice-symmetry, wurtzite (wz) and zinc-blende (zb), coexist in the GaN nanotripods. Periodical transformation between wz and zb drives the epitaxy of the hierarchical nanotripods with N-polarity. The zb-GaN is formed by the poor diffusion of adatoms, and it can be suppressed by improving the ability of the Ga adatoms to migrate as the growth temperature increased. This controllable epitaxy of hierarchical GaN nanotripods allows quantum dots to be located at the phase junctions of the nanotripods and nanowires, suggesting a new recipe for multichannel quantum devices.

  15. Synchrotron X-ray diffraction analysis of epitaxial GaN layer laterally overgrown

    Feng Gan; Wang Yu Tian; Yang Hui; Liang Jun Wu; Zheng Wen Li; Jia Quan Jie


    The GaN layer grown by epitaxial lateral overgrowth on sapphire (0001) has been investigated by synchrotron X-ray diffraction. The results show that ELO GaN stripes bend towards the SiN sub x mask in directions perpendicular to the stripe direction. This lead to the GaN (0001) crystal planes in the 'wings' (overgrown GaN) exhibit crystallographic tilts away from those in the 'window' (seed) regions. The GaN (0002) diffraction was used to determine the grain sizes in the wing region and window region, respectively. It is found that the grain size in the wing region increases about three times comparing to those in window region

  16. Prospects for the application of GaN power devices in hybrid electric vehicle drive systems

    Su, Ming; Chen, Chingchi; Rajan, Siddharth


    GaN, a wide bandgap semiconductor successfully implemented in optical and high-speed electronic devices, has gained momentum in recent years for power electronics applications. Along with rapid progress in material and device processing technologies, high-voltage transistors over 600 V have been reported by a number of teams worldwide. These advances make GaN highly attractive for the growing market of electrified vehicles, which currently employ bipolar silicon devices in the 600-1200 V class for the traction inverter. However, to capture this billion-dollar power market, GaN has to compete with existing IGBT products and deliver higher performance at comparable or lower cost. This paper reviews key achievements made by the GaN semiconductor industry, requirements of the automotive electric drive system and remaining challenges for GaN power devices to fit in the inverter application of hybrid vehicles.

  17. GaN: From three- to two-dimensional single-layer crystal and its multilayer van der Waals solids

    Onen, A.; Kecik, D.; Durgun, E.; Ciraci, S.


    Three-dimensional (3D) GaN is a III-V compound semiconductor with potential optoelectronic applications. In this paper, starting from 3D GaN in wurtzite and zinc-blende structures, we investigated the mechanical, electronic, and optical properties of the 2D single-layer honeycomb structure of GaN (g -GaN ) and its bilayer, trilayer, and multilayer van der Waals solids using density-functional theory. Based on high-temperature ab initio molecular-dynamics calculations, we first showed that g -GaN can remain stable at high temperature. Then we performed a comparative study to reveal how the physical properties vary with dimensionality. While 3D GaN is a direct-band-gap semiconductor, g -GaN in two dimensions has a relatively wider indirect band gap. Moreover, 2D g -GaN displays a higher Poisson ratio and slightly less charge transfer from cation to anion. In two dimensions, the optical-absorption spectra of 3D crystalline phases are modified dramatically, and their absorption onset energy is blueshifted. We also showed that the physical properties predicted for freestanding g -GaN are preserved when g -GaN is grown on metallic as well as semiconducting substrates. In particular, 3D layered blue phosphorus, being nearly lattice-matched to g -GaN , is found to be an excellent substrate for growing g -GaN . Bilayer, trilayer, and van der Waals crystals can be constructed by a special stacking sequence of g -GaN , and they can display electronic and optical properties that can be controlled by the number of g -GaN layers. In particular, their fundamental band gap decreases and changes from indirect to direct with an increasing number of g -GaN layers.

  18. Preparation of Porous GaN Buffer and Its Influence on the Residual Stress of GaN Epilayers Grown by Hydride Vapor Phase Epitaxy


    The preparation of porous structure on the molecular beam epitaxy (MBE)-grown mixed-polarity GaN epilayers was reported by using the wet chemical etching method. The effect of this porous structure on the residual stress of subsequent-growth GaN epilayers was studied by Raman and photoluminescence (PL) spectrum.Substantial decrease in the biaxial stresse can be achieved by employing the porous buffers in the hydride vapour phase epitaxy (HVPE) epilayer growth.

  19. Ab initio investigations of the strontium gallium nitride ternaries Sr 3GaN3 and Sr6GaN5: Promising materials for optoelectronic

    Goumri-Said, Souraya


    Sr3GaN3 and Sr6GaN5 could be promising potential materials for applications in the microelectronics, optoelectronics and coating materials areas of research. We studied in detail their structural, elastic, electronic, optical as well as the vibrational properties, by means of density functional theory framework. Both of these ternaries are semiconductors, where Sr3GaN3 exhibits a small indirect gap whereas Sr6GaN5 has a large direct gap. Indeed, their optical properties are reported for radiation up to 40 eV. Charge densities contours, Hirshfeld and Mulliken populations, are reported to investigate the role of each element in the bonding. From the mechanical properties calculation, it is found that Sr6GaN5 is harder than Sr3GaN3, and the latter is more anisotropic than the former. The phonon dispersion relation, density of phonon states and the vibrational stability are reported from the density functional perturbation theory calculations. © 2013 IOP Publishing Ltd.

  20. Current steering effect of GaN nanoporous structure

    Lin, Chia-Feng, E-mail: [Department of Materials Science and Engineering, National Chung Hsing University, Taichung 402, Taiwan (China); Department of Electrical Engineering, Yale University, New Haven, CT 06520 (United States); Wang, Jing-Hao; Cheng, Po-Fu; Tseng, Wang-Po; Fan, Feng-Hsu; Wu, Kaun-Chun; Lee, Wen-Che [Department of Materials Science and Engineering, National Chung Hsing University, Taichung 402, Taiwan (China); Han, Jung [Department of Electrical Engineering, Yale University, New Haven, CT 06520 (United States)


    Current steering effect of InGaN light emitting diode (LED) structure was demonstrated by forming a high resistivity GaN nanoporous structure. Disk-array patterns with current-injection bridge structures were fabricated on InGaN LED devices through a focused ion beam (FIB) system. GaN nanoporous structure was formed around the FIB-drilled holes through a electrochemical (EC) wet-etching process on a n-type GaN:Si layer under the InGaN active layer. High emission intensity and small peak wavelength blueshift phenomenon of the electroluminescence spectra were observed in the EC-treated region compared with the non-treated region. The branch-like nanoporous structure was formed along the lateral etched direction to steer the injection current in 5 μm-width bridge structures. In the FIB-drilled hole structure, high light emission intensity of the central-disk region was observed by enlarging the bridge width to 10 μm, with a 5 μm EC-treated width, that reduced the current steering effect and increased the light scattering effect on the nanoporous structure. The EC-treated GaN:Si nanoporous structure acted as a high light scattering structure and a current steering structure that has potential on the current confinement for vertical cavity surface emitting laser applications. - Highlights: • High resistivity nanoporous-GaN formed in InGaN LED through electrochemical process. • Branch-like nanoporous in 5 μm-width bridge structure can steer the injection current. • Nanoporous GaN acted as s light scattering and current steering structures in InGaN LED.

  1. Devices for medical diagnosis with GaN lasers

    Kwasny, Miroslaw; Mierczyk, Zygmunt


    This paper presents laser-induced fluroescence method (LIF) employing endogenous ("autofluroescence") and exogenous fluorophores. LIF is applied for clinical diagnosis in dermatology, gynaecology, urology, lung tumors as well as for early dentin caries. We describe the analysers with He-Ne, He-Cd, and SHG Nd:YAG lasers and new generation systems based on blue semiconductor GaN lasers that have been implemented into clinical practice till now. The LIF method, fundamental one for many medical applications, with excitation radiation of wavelength 400 nm could be appl,ied only using tunable dye lasers or titanium lasers adequte for laboratory investigations. Development of GaN laser shows possibility to design portable, compact diagnostic devices as multi-channel analysers of fluorescence spectra and surface imaging devoted to clinical application. The designed systems used for spectra measurement and registration of fluorescence images include lasers of power 5-30 mW and generate wavelengths of 405-407 nm. They are widely used in PDT method for investigation of superficial distribution of accumulation kinetics of all known photosensitizers, their elimination, and degradation as well as for treatment of superficial lesions of mucosa and skin. Excitation of exogenous porphrins in Soret band makes possible to estimate their concentration and a period of healthy skin photosensitivity that occurs after photosensitiser injections. Due to high sensitivity of spectrum analysers, properties of photosensitisers can be investigated in vitro (e.g. their aggregation, purity, chromatographic distributions) when their concentrations are 2-3 times lower in comparison to concentrations investigated with typical spectrofluorescence methods. Dentistry diagnosis is a new field in which GaN laser devices can be applied. After induction with blue light, decreased autofluorescence intensity can be observed when dentin caries occur and strong characteristic bands of endogenous porphyrines

  2. GaN Nanowire Devices: Fabrication and Characterization

    Scott, Reum

    The development of microelectronics in the last 25 years has been characterized by an exponential increase of the bit density in integrated circuits (ICs) with time. Scaling solid-state devices improves cost, performance, and power; as such, it is of particular interest for companies, who gain a market advantage with the latest technology. As a result, the microelectronics industry has driven transistor feature size scaling from 10 μm to ~30 nm during the past 40 years. This trend has persisted for 40 years due to optimization, new processing techniques, device structures, and materials. But when noting processor speeds from the 1970's to 2009 and then again in 2010, the implication would be that the trend has ceased. To address the challenge of shrinking the integrated circuit (IC), current research is centered on identifying new materials and devices that can supplement and/or potentially supplant it. Bottom-up methods tailor nanoscale building blocks---atoms, molecules, quantum dots, and nanowires (NWs)---to be used to overcome these limitations. The Group IIIA nitrides (InN, AlN, and GaN) possess appealing properties such as a direct band gap spanning the whole solar spectrum, high saturation velocity, and high breakdown electric field. As a result nanostructures and nanodevices made from GaN and related nitrides are suitable candidates for efficient nanoscale UV/ visible light emitters, detectors, and gas sensors. To produce devices with such small structures new fabrication methods must be implemented. Devices composed of GaN nanowires were fabricated using photolithography and electron beam lithography. The IV characteristics of these devices were noted under different illuminations and the current tripled from 4.8*10-7 A to 1.59*10 -6 A under UV light which persisted for at least 5hrs.

  3. Visible fiber lasers excited by GaN laser diodes

    Fujimoto, Yasushi; Nakanishi, Jun; Yamada, Tsuyoshi; Ishii, Osamu; Yamazaki, Masaaki


    This paper describes and discusses visible fiber lasers that are excited by GaN laser diodes. One of the attractive points of visible light is that the human eye is sensitive to it between 400 and 700 nm, and therefore we can see applications in display technology. Of course, many other applications exist. First, we briefly review previously developed visible lasers in the gas, liquid, and solid-state phases and describe the history of primary solid-state visible laser research by focusing on rare-earth doped fluoride media, including glasses and crystals, to clarify the differences and the merits of primary solid-state visible lasers. We also demonstrate over 1 W operation of a Pr:WPFG fiber laser due to high-power GaN laser diodes and low-loss optical fibers (0.1 dB/m) made by waterproof fluoride glasses. This new optical fiber glass is based on an AlF3 system fluoride glass, and its waterproof property is much better than the well known fluoride glass of ZBLAN. The configuration of primary visible fiber lasers promises highly efficient, cost-effective, and simple laser systems and will realize visible lasers with photon beam quality and quantity, such as high-power CW or tunable laser systems, compact ultraviolet lasers, and low-cost ultra-short pulse laser systems. We believe that primary visible fiber lasers, especially those excited by GaN laser diodes, will be effective tools for creating the next generation of research and light sources.

  4. Characterization of GaN Nanorods Fabricated Using Ni Nanomasking and Reactive Ion Etching: A Top-Down Approach

    Ashutosh Kumar


    Full Text Available Large thermal mismatch between GaN surface and sapphire results in compressive stress in Gallium Nitride (GaN layer which degrades the device performance. Nanostructuring the GaN can reduce this stress leading to reduction in Quantum Confined Stark Effect. Aligned GaN nanorods based nanodevices have potential applications in electronics and optoelectronics. This paper describes the fabrication of GaN nanorods using Ni nanomasking and reactive ion etching. The morphology of GaN nanorods was studied by field emission scanning electron microscopy. The optical properties of GaN nanorods were studied by Cathodoluminescence (CL spectroscopy. CL results revealed the existence of characteristic band-edge luminescence and yellow band luminescence.

  5. MOCVD growth of GaN on Si through novel substrate modification techniques

    Gagnon, Jarod C.

    GaN is a semiconductor material with great potential for use in high power electronics and optoelectronics due to the high electron mobility, high breakdown voltage, high thermal stability, and large direct bandgap of GaN. Si is a desirable substrate material for GaN heteroepitaxy due to the low cost of production, large wafer sizes available, and current widespread use in the electronics industry. The growth of GaN/Si devices suffers from the lattice and CTE mismatches between GaN and Si and therefore multiple methods of strain reduction have been employed to counter these effects. In this work we presented two novel methods of substrate modification to promote the growth of device quality GaN on Si. Initial work focused on the implantation of AlN/Si(111) substrates with N+ ions below the AlN/Si(111) interface. A reduction in the initial compressive stress in GaN films as well as the degree of tensile stress generation during growth was observed on implanted samples. Optical microscopy of the GaN surfaces showed reduced channeling crack density on implanted substrates. Transmission electron microscopy (TEM) studies showed a disordered layer in the Si substrate at the implantation depth which consisted of a mixture of polycrystalline and amorphous Si. Evidence was provided to suggest that the disordered layer at the implantation depth was acting as a compliant layer which decoupled the GaN film from the bulk Si substrate and partially accommodated the tensile stress formed during growth and cooling. A reduction in threading dislocation (TD) density on ion implanted substrates was also observed. Additional studies showed that by increasing the lateral size of AlN islands, the tensile growth stress and TD density in GaN films on ion implanted substrates could be further reduced. XRD studies showed an expansion of the AlN lattice on implanted substrates with larger lateral island sizes. The final tensile growth stress of films on implanted substrates was further

  6. Field emission from quantum size GaN structures

    Yilmazoglu, O.; Pavlidis, D.; Litvin, Yu. M.; Hubbard, S.; Tiginyanu, I. M.; Mutamba, K.; Hartnagel, H. L.; Litovchenko, V. G.; Evtukh, A.


    Whisker structures and quantum dots fabricated by photoelectrochemical (PEC) etching of undoped and doped metalorganic chemical vapor deposition (MOCVD)-grown GaN (2×10 17 or 3×10 18 cm -3) are investigated in relation with their field-emission characteristics. Different surface morphologies, corresponding to different etching time and photocurrent, results in different field-emission characteristics with low turn-on voltage down to 4 V/μm and the appearance of quantum-size effect in the I- V curves.

  7. Field emission from quantum size GaN structures

    Yilmazoglu, O.; Pavlidis, D.; Litvin, Yu.M.; Hubbard, S.; Tiginyanu, I.M.; Mutamba, K.; Hartnagel, H.L.; Litovchenko, V.G.; Evtukh, A


    Whisker structures and quantum dots fabricated by photoelectrochemical (PEC) etching of undoped and doped metalorganic chemical vapor deposition (MOCVD)-grown GaN (2x10{sup 17} or 3x10{sup 18} cm{sup -3}) are investigated in relation with their field-emission characteristics. Different surface morphologies, corresponding to different etching time and photocurrent, results in different field-emission characteristics with low turn-on voltage down to 4 V/{mu}m and the appearance of quantum-size effect in the I-V curves.

  8. Photoluminescence study on Eu-implanted GaN

    Zhang Chun-Guang; Bian Liu-Fang; Chen Wei-De


    The photoluminescence (PL) properties of Eu-implanted GaN thin films are studied. The experimental results show that the PL intensity is seriously affected by ion implantation conditions. The PL efficiency increases exponentially with annealing temperature increasing up to a maximum temperature of 1050℃. Moreover, the PL intensity for the sample implanted along the channelling direction is nearly twice more than that observed from the sample implanted along the random direction. The thermal quenching of PL intensity from 10K to 300K for sample annealed at 1050℃ is only 42.%.

  9. Acceptor and donor impurities in GaN nanocrystals

    Echeverría-Arrondo, C.; Pérez-Conde, J.; Bhattacharjee, A. K.


    We investigate acceptor and donor states in GaN nanocrystals doped with a single substitutional impurity. Quantum dots (QD's) of zinc-blende structure and spherical shape are considered with the radius ranging from 4.5 to 67.7 A. The size-dependent energy spectra are calculated within the sp3d5s* tight-binding model, which yields a good agreement with the confinement-induced blue shifts observed in undoped QD's. The computed binding energy is strongly enhanced with respect to the experimental...

  10. Stress related aspects of GaN technology physics

    Suhir, Ephraim


    Simple, easy-to-use and physically meaningful analytical models have been developed for the assessment of the combined effect of the lattice and thermal mismatch on the induced stresses in an elongated bi-material assembly, as well as on the thermal mismatch on the thermal stresses in a tri-material assembly, in which the lattice mismatched stresses are eliminated in one way or another. This could be done, e.g., by using a polished or an etched substrate. The analysis is carried out in application to Gallium Nitride (GaN)-Silicon Carbide (SiC) and GaN-diamond (C) filmsubstrate assemblies. The calculated data are obtained, assuming that no annealing or other stress reduction means is applied. The data agree reasonably well with the reported (available) in-situ measurements. The most important conclusion from the computed data is that even if a reasonably good lattice match takes place (as, e.g., in the case of a GaN film fabricated on a SiC substrate, when the mismatch strain is only about 3%) and, in addition, the temperature change (from the fabrication/growth temperature to the operation temperature) is significant (as high as 1000 °C), the thermal stresses are still considerably lower than the lattice-mismatch stresses. Although there are structural and technological means for further reduction of the lattice-mismatch stresses (e.g., by high temperature annealing or by providing one or more buffering layers, or by using patterned or porous substrates), there is still a strong incentive to eliminate completely the lattice mismatch stresses. This seems to be indeed possible, if polished or otherwise flattened (e.g., chemically etched) substrates and sputter deposited GaN film is employed. In such a case only thermal stresses remain, but even these could be reduced, if necessary, by using compliant buffering layers, including layers of variable compliance, or by introducing variable compliance into the properly engineered substrate. In any event, it is expected

  11. Pressure-induced phase transition in GaN nanocrystals

    Cui, Q; Zhang, W; Wang, X; Zhang, J; Cui, T; Xie, Y; Liu, J; Zou, G


    High-pressure in situ energy-dispersive x-ray diffraction experiments on GaN nanocrystals with 50 nm diameter have been carried out using a synchrotron x-ray source and a diamond-anvil cell up to about 79 GPa at room temperature. A pressure-induced first-order structural phase transition from the wurtzite-type structure to the rock-salt-type structure starts at about 48.8 GPa. The rock-salt-type phase persists to the highest pressure in our experimental range.

  12. Modelling of GaN quantum dot terahertz cascade laser

    Asgari, A.; Khorrami, A. A.


    In this paper GaN based spherical quantum dot cascade lasers has been modelled, where the generation of the terahertz waves are obtained. The Schrödinger, Poisson, and the laser rate equations have been solved self-consistently including all dominant physical effects such as piezoelectric and spontaneous polarization in nitride-based QDs and the effects of the temperature. The exact value of the energy levels, the wavefunctions, the lifetimes of electron levels, and the lasing frequency are calculated. Also the laser parameters such as the optical gain, the output power and the threshold current density have been calculated at different temperatures and applied electric fields.

  13. Photoluminescence enhancement from GaN by beryllium doping

    García-Gutiérrez, R.; Ramos-Carrazco, A.; Berman-Mendoza, D.; Hirata, G. A.; Contreras, O. E.; Barboza-Flores, M.


    High quality Be-doped (Be = 0.19 at.%) GaN powder has been grown by reacting high purity Ga diluted alloys (Be-Ga) with ultra high purity ammonia in a horizontal quartz tube reactor at 1200 °C. An initial low-temperature treatment to dissolve ammonia into the Ga melt produced GaN powders with 100% reaction efficiency. Doping was achieved by dissolving beryllium into the gallium metal. The powders synthesized by this method regularly consist of two particle size distributions: large hollow columns with lengths between 5 and 10 μm and small platelets in a range of diameters among 1 and 3 μm. The GaN:Be powders present a high quality polycrystalline profile with preferential growth on the [10 1 bar 1] plane, observed by means of X-ray diffraction. The three characteristics growth planes of the GaN crystalline phase were found by using high resolution TEM microscopy. The optical enhancing of the emission in the GaN powder is attributed to defects created with the beryllium doping. The room temperature photoluminescence emission spectra of GaN:Be powders, revealed the presence of beryllium on a shoulder peak at 3.39 eV and an unusual Y6 emission at 3.32eV related to surface donor-acceptor pairs. Also, a donor-acceptor-pair transition at 3.17 eV and a phonon replica transition at 3.1 eV were observed at low temperature (10 K). The well-known yellow luminescence band coming from defects was observed in both spectra at room and low temperature. Cathodoluminescence emission from GaN:Be powders presents two main peaks associated with an ultraviolet band emission and the yellow emission known from defects. To study the trapping levels related with the defects formed in the GaN:Be, thermoluminescence glow curves were obtained using UV and β radiation in the range of 50 and 150 °C.

  14. Effect of reactor pressure on the growth rate and structural properties of GaN films

    NI JinYu; HAO Yue; ZHANG JinCheng; YANG LinAn


    The effect of reactor pressure on the growth rate,surface morphology and crystalline quality of GaN films grown on sapphire by metalorganic chemical vapor deposition is studied.The results show that as the reactor pressure increases from 2500 to 20000 Pa,the GaN surface becomes rough and the growth rate of GaN films decreases.The rough surface morphology is associated with the initial high temperature GaN islands,which are large with low density due to low adatom surface diffusion under high reactor pressure.These islands prolong the occurrence of 2D growth mode and decrease the growth rate of GaN film.Meanwhile,the large GaN islands with low density lead to the reduction of threading dislocation density during subsequent island growth and coalescence,and consequently decrease the full width at half maximum of X-ray rocking curve of the GaN film.

  15. Nanoscratch Characterization of GaN Epilayers on c- and a-Axis Sapphire Substrates

    Wen Hua-Chiang


    Full Text Available Abstract In this study, we used metal organic chemical vapor deposition to form gallium nitride (GaN epilayers on c- and a-axis sapphire substrates and then used the nanoscratch technique and atomic force microscopy (AFM to determine the nanotribological behavior and deformation characteristics of the GaN epilayers, respectively. The AFM morphological studies revealed that pile-up phenomena occurred on both sides of the scratches formed on the GaN epilayers. It is suggested that cracking dominates in the case of GaN epilayers while ploughing during the process of scratching; the appearances of the scratched surfaces were significantly different for the GaN epilayers on the c- and a-axis sapphire substrates. In addition, compared to the c-axis substrate, we obtained higher values of the coefficient of friction (μ and deeper penetration of the scratches on the GaN a-axis sapphire sample when we set the ramped force at 4,000 μN. This discrepancy suggests that GaN epilayers grown on c-axis sapphire have higher shear resistances than those formed on a-axis sapphire. The occurrence of pile-up events indicates that the generation and motion of individual dislocation, which we measured under the sites of critical brittle transitions of the scratch track, resulted in ductile and/or brittle properties as a result of the deformed and strain-hardened lattice structure.

  16. GaN quantum dot polarity determination by X-ray photoelectron diffraction

    Romanyuk, O.; Bartoš, I.; Brault, J.; Mierry, P. De; Paskova, T.; Jiříček, P.


    Growth of GaN quantum dots (QDs) on polar and semipolar GaN substrates is a promising technology for efficient nitride-based light emitting diodes (LED). The QDs crystal orientation typically repeats the polarity of the substrate. In case of non-polar or semipolar substrates, the polarity of QDs is not obvious. In this article, the polarity of GaN QDs and of underlying layers was investigated nondestructively by X-ray photoelectron diffraction (XPD). Polar and semipolar GaN/Al0.5Ga0.5N heterostructures were grown on the sapphire substrates with (0001) and (1 1 bar 00) orientations by molecular beam epitaxy (MBE). Polar angle dependence of N 1s core-level photoelectron intensities were measured from GaN QDs and compared with the corresponding experimental curves from free-standing GaN crystals. It is confirmed experimentally, that the crystalline orientation of polar (0001) GaN QDs follows the orientation of the (0001) sapphire substrate. In case of semipolar GaN QDs grown on (1 1 bar 00) sapphire substrate, the (11 2 bar 2) polarity of QDs was determined.

  17. Influence of surface scattering on the thermal properties of spatially confined GaN nanofilm

    Hou, Yang; Zhu, Lin-Li


    Gallium nitride (GaN), the notable representative of third generation semiconductors, has been widely applied to optoelectronic and microelectronic devices due to its excellent physical and chemical properties. In this paper, we investigate the surface scattering effect on the thermal properties of GaN nanofilms. The contribution of surface scattering to phonon transport is involved in solving a Boltzmann transport equation (BTE). The confined phonon properties of GaN nanofilms are calculated based on the elastic model. The theoretical results show that the surface scattering effect can modify the cross-plane phonon thermal conductivity of GaN nanostructures completely, resulting in the significant change of size effect on the conductivity in GaN nanofilm. Compared with the quantum confinement effect, the surface scattering leads to the order-of-magnitude reduction of the cross-plane thermal conductivity in GaN nanofilm. This work could be helpful for controlling the thermal properties of GaN nanostructures in nanoelectronic devices through surface engineering. Project supported by the National Natural Science Foundation of China (Grant Nos. 11302189 and 11321202) and the Doctoral Fund of Ministry of Education of China (Grant No. 20130101120175).

  18. Growth of GaN nanowall network on Si (111) substrate by molecular beam epitaxy.

    Zhong, Aihua; Hane, Kazuhiro


    GaN nanowall network was epitaxially grown on Si (111) substrate by molecular beam epitaxy. GaN nanowalls overlap and interlace with one another, together with large numbers of holes, forming a continuous porous GaN nanowall network. The width of the GaN nanowall can be controlled, ranging from 30 to 200 nm by adjusting the N/Ga ratio. Characterization results of a transmission electron microscope and X-ray diffraction show that the GaN nanowall is well oriented along the C axis. Strong band edge emission centered at 363 nm is observed in the spectrum of room temperature photoluminescence, indicating that the GaN nanowall network is of high quality. The sheet resistance of the Si-doped GaN nanowall network along the lateral direction was 58 Ω/. The conductive porous nanowall network can be useful for integrated gas sensors due to the large surface area-to-volume ratio and electrical conductivity along the lateral direction by combining with Si micromachining.

  19. One-step graphene coating of heteroepitaxial GaN films.

    Choi, Jae-Kyung; Huh, Jae-Hoon; Kim, Sung-Dae; Moon, Daeyoung; Yoon, Duhee; Joo, Kisu; Kwak, Jinsung; Chu, Jae Hwan; Kim, Sung Youb; Park, Kibog; Kim, Young-Woon; Yoon, Euijoon; Cheong, Hyeonsik; Kwon, Soon-Yong


    Today, state-of-the-art III-Ns technology has been focused on the growth of c-plane nitrides by metal-organic chemical vapor deposition (MOCVD) using a conventional two-step growth process. Here we show that the use of graphene as a coating layer allows the one-step growth of heteroepitaxial GaN films on sapphire in a MOCVD reactor, simplifying the GaN growth process. It is found that the graphene coating improves the wetting between GaN and sapphire, and, with as little as ~0.6 nm of graphene coating, the overgrown GaN layer on sapphire becomes continuous and flat. With increasing thickness of the graphene coating, the structural and optical properties of one-step grown GaN films gradually transition towards those of GaN films grown by a conventional two-step growth method. The InGaN/GaN multiple quantum well structure grown on a GaN/graphene/sapphire heterosystem shows a high internal quantum efficiency, allowing the use of one-step grown GaN films as 'pseudo-substrates' in optoelectronic devices. The introduction of graphene as a coating layer provides an atomic playground for metal adatoms and simplifies the III-Ns growth process, making it potentially very useful as a means to grow other heteroepitaxial films on arbitrary substrates with lattice and thermal mismatch.

  20. The influence of Fe doping on the surface topography of GaN epitaxial material

    Lei, Cui; Haibo, Yin; Lijuan, Jiang; Quan, Wang; Chun, Feng; Hongling, Xiao; Cuimei, Wang; Jiamin, Gong; Bo, Zhang; Baiquan, Li; Xiaoliang, Wang; Zhanguo, Wang


    Fe doping is an effective method to obtain high resistivity GaN epitaxial material. But in some cases, Fe doping could result in serious deterioration of the GaN material surface topography, which will affect the electrical properties of two dimensional electron gas (2DEG) in HEMT device. In this paper, the influence of Fe doping on the surface topography of GaN epitaxial material is studied. The results of experiments indicate that the surface topography of Fe-doped GaN epitaxial material can be effectively improved and the resistivity could be increased after increasing the growth rate of GaN materials. The GaN material with good surface topography can be manufactured when the Fe doping concentration is 9 × 1019 cm-3. High resistivity GaN epitaxial material which is 1 × 109 Ω·cm is achieved. Project supported by the Knowledge Innovation Engineering of the Chinese Academy of Sciences (No. YYY-0701-02), the National Natural Science Foundation of China (Nos. 61204017, 61334002), the State Key Development Program for Basic Research of China, and the National Science and Technology Major Project.

  1. Photoelectrochemical water splitting on nanoporous GaN thin films for energy conversion under visible light

    Cao, Dezhong; Xiao, Hongdi; Fang, Jiacheng; Liu, Jianqiang; Gao, Qingxue; Liu, Xiangdong; Ma, Jin


    Nanoporous (NP) GaN thin films, which were fabricated by an electrochemical etching method at different voltages, were used as photoelectrodes during photoelectrochemical (PEC) water splitting in 1 M oxalic acid solution. Upon illumination at a power density of 100 mW cm‑2 (AM 1.5), water splitting is observed in NP GaN thin films, presumably resulting from the valence band edge which is more positive than the redox potential of the oxidizing species. In comparison with NP GaN film fabricated at 8 V, NP GaN obtained at 18 V shows nearly twofold enhancement in photocurrent with the maximum photo-to-hydrogen conversion efficiency of 1.05% at ~0 V (versus Ag/AgCl). This enhancement could be explained with (i) the increase of surface area and surface states, and (ii) the decrease of resistances and carrier concentration in the NP GaN thin films. High stability of the NP GaN thin films during the PEC water splitting further confirms that the NP GaN thin film could be applied to the design of efficient solar cells and solar fuel devices.

  2. Design, fabrication and characterising of 100 W GaN HEMT for Ku-band application

    Chunjiang, Ren; Shichang, Zhong; Yuchao, Li; Zhonghui, Li; Yuechan, Kong; Tangsheng, Chen


    Ku-band GaN power transistor with output power over 100 W under the pulsed operation mode is presented. A high temperature A1N nucleation together with an Fe doped GaN buffer was introduced for the developed GaN HEMT. The AlGaN/GaN hetero-structure deposited on 3 inch SiC substrate exhibited a 2DEG hall mobility and density of ˜2100 cm2/(V·s) and 1.0 × 1013 cm-2, respectively, at room temperature. Dual field plates were introduced to the designed 0.25 μm GaN HEMT and the source connected field plate was optimized for minimizing the peak field plate near the drain side of the gate, while maintaining excellent power gain performance for Ku-band application. The load-pull measurement at 14 GHz showed a power density of 5.2 W/mm for the fabricated 400 μm gate periphery GaN HEMT operated at a drain bias of 28 V. A Ku-band internally matched GaN power transistor was developed with two 10.8 mm gate periphery GaN HEMT chips combined. The GaN power transistor exhibited an output power of 102 W at 13.3 GHz and 32 V operating voltage under pulsed operation mode with a pulse width of 100 μs and duty cycle of 10%. The associated power gain and power added efficiency were 9.2 dB and 48%, respectively. To the best of the authors' knowledge, the PAE is the highest for Ku-band GaN power transistor with over 100 W output power.

  3. Research on quantum efficiency of GaN wire photocathode

    Xia, Sihao; Liu, Lei; Diao, Yu; Kong, Yike


    On the basis of three-dimensional continuity equation in semiconductors and finite difference method, the carrier concentration and the quantum efficiency of GaN wire photocathode as a function of incident photon energy are achieved. Results show that the quantum efficiency of the wire photocathode is largely enhanced compared with the conventional planar photocathode. The superiority of the wire photocathode is reflected in its structure with surrounding surfaces. The quantum efficiency of the wire photocathode largely depends on the wire width, surface reflectivity, surface escape probability and incident angle of light. The back interface recombination rate, however, has little influences on the quantum efficiency of the wire photocathode. The simulation results suggest that the optimal width for photoemission is 150-200 nm. Besides, the quantum efficiency increases and decreases linearly with increasing surface escape probability and surface reflectivity, respectively. With increasing ratio of wire spacing to wire height, the optimal incident angle of light is reduced. These simulations are expected to guide the preparation of a better performing GaN wire photocathode.

  4. Radiotracer Spectroscopy on Group II Acceptors in GaN


    The semiconductor GaN is already used for the production of high power light emitting diodes in the blue and UV spectral range. But the $\\rho$-type doping, which is usually obtained by Mg doping, is still inefficient due to compensation and passivation effects caused by defects present in the material. It is theoretically predicted, that Be is a more promising candidate for $\\rho$-doping with a lower ionization energy of 60meV. It is our goal to investigate the electrical and optical properties of Be- and Mg-related defects in GaN to clarify the problem of compensation and passivation. The used methods are standard spectroscopic methods in semiconductor physics which are improved by using radioactive isotopes. The radioactive decay of $^{7}$Be and $^{28}$Mg is used to clearly correlate different signals with Be or Mg related defects. We intend to use the spectroscopic techniques Deep Level Transient Spectroscopy (DLTS), Thermal Admittance Spectroscopy (TAS), photoluminescence (PL) and additionally Hall-effect...

  5. A GaN photonic crystal membrane laser.

    Lin, Cheng-Hung; Wang, Jyh-Yang; Chen, Cheng-Yen; Shen, Kun-Ching; Yeh, Dong-Ming; Kiang, Yean-Woei; Yang, C C


    The implementation of a series of optically pumped GaN photonic crystal (PhC) membrane lasers is demonstrated at room temperature. The photonic crystal is composed of a scalene-triangular arrangement of circular holes in GaN. Three defect structures are fabricated for comparing their lasing characteristics with those of perfect PhC. It is observed that all the lasing defect modes have lasing wavelengths very close to the band-edge modes in the perfect PhC structure. Although those lasing modes, including band-edge and defect modes, have different optical pump thresholds, different lasing spectral widths, different quality factors (Q factors), and different polarization ratios, all their polarization distributions show maxima in the directions around one of the hole arrangement axes. The similar lasing characteristics between the band-edge and defect modes are attributed to the existence of extremely narrow partial band gaps for forming the defect modes. Also, the oriented polarization properties are due to the scalene-triangle PhC structure. In one of the defect lasing modes, the lasing threshold is as low as 0.82 mJ cm(-2), the cavity Q factor is as large as 1743, and the polarization ratio is as large as 25.4. Such output parameters represent generally superior lasing behaviors when compared with previously reported implementations of similar laser structures.

  6. Orthodox etching of HVPE-grown GaN

    Weyher, J.L.; Lazar, S.; Macht, L.; Liliental-Weber, Z.; Molnar,R.J.; Muller, S.; Nowak, G.; Grzegory, I.


    Orthodox etching of HVPE-grown GaN in molten eutectic of KOH + NaOH (E etch) and in hot sulfuric and phosphoric acids (HH etch) is discussed in detail. Three size grades of pits are formed by the preferential E etching at the outcrops of threading dislocations on the Ga-polar surface of GaN. Using transmission electron microscopy (TEM) as the calibration tool it is shown that the largest pits are formed on screw, intermediate on mixed and the smallest on edge dislocations. This sequence of size does not follow the sequence of the Burgers values (and thus the magnitude of the elastic energy) of corresponding dislocations. This discrepancy is explained taking into account the effect of decoration of dislocations, the degree of which is expected to be different depending on the lattice deformation around the dislocations, i.e. on the edge component of the Burgers vector. It is argued that the large scatter of optimal etching temperatures required for revealing all three types of dislocations in HVPE-grown samples from different sources also depends upon the energetic status of dislocations. The role of kinetics for reliability of etching in both etches is discussed and the way of optimization of the etching parameters is shown.

  7. Gas source molecular beam epitaxial growth of GaN

    Brown, Duncan W.


    Aluminum gallium nitride (AlGaN) has long been recognized as a promising radiation hard optoelectronic material. AlGaN has a wide direct band gap and therefore has potential applications in the fabrication of short wave-length devices, e.g., detectors and light-emitting diodes in the visible to ultraviolet region. Additionally, its piezoelectric properties and high acoustic velocities make it attractive for acoustic devices. The technical objective in Phase 1 was to determine if low temperature sources based on covalently bonded Group 3-nitrogen compounds could be used to prepare AlGaN films by gas source molecular beam epitaxy. The program required to investigate low temperature AlGaN source materials was separated into two parts: (1) the synthesis, purification, and pyrolysis of gallium-nitrogen adducts and aluminum-nitrogen adducts; and (2) the growth of GaN by chemical beam epitaxy. We clearly demonstrated under CBE conditions GaN(x)C(y) films could be grown using compounds with pre-existing Ga-N bonds whereas no films were formed using trimethylgallium. Dimethylgallium amide was shown to produce dramatically lower carbon content films in the presence of ammonia than did trimethylgallium in the presence of ammonia.

  8. High Quality, Low Cost Ammonothermal Bulk GaN Substrates

    Ehrentraut, D; Pakalapati, RT; Kamber, DS; Jiang, WK; Pocius, DW; Downey, BC; McLaurin, M; D' Evelyn, MP


    Ammonothermal GaN growth using a novel apparatus has been performed on c-plane, m-plane, and semipolar seed crystals with diameters between 5 mm and 2 in. to thicknesses of 0.5-3 mm. The highest growth rates are greater than 40 mu m/h and rates in the 10-30 mu m/h range are routinely observed for all orientations. These values are 5-100x larger than those achieved by conventional ammonothermal GaN growth. The crystals have been characterized by X-ray diffraction rocking-curve (XRC) analysis, optical and scanning electron microscopy (SEM), cathodoluminescence (CL), optical spectroscopy, and capacitance-voltage measurements. The crystallinity of the grown crystals is similar to or better than that of the seed crystals, with FWHM values of about 20-100 arcsec and dislocation densities of 1 x 10(5)-5 x 10(6) cm(-2). Dislocation densities below 10(4) cm(-2) are observed in laterally-grown crystals. Epitaxial InGaN quantum well structures have been successfully grown on ammonothermal wafers. (C) 2013 The Japan Society of Applied Physics

  9. X-ray detection with GaN thin films

    Hofstetter, Markus; Schmid, Martin; Thalhammer, Stefan [Helmholtz Zentrum Muenchen, Institute for Radiation Protection, Ingolstaedter Landstrasse 1, D-85764 Neuherberg (Germany); Howgate, John; Stutzmann, Martin [Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall 3, D-85748 Garching (Germany)


    In recent years precise miniature-dosimeters for real-time detection of X-rays in medicine have been developed with two aspects to monitor radiation in the region of interest and to improve therapeutic methods. Sensors include Germanium or Silicon photoconductive detectors, MOSFETs, and PIN-diodes. While miniaturization of these systems for spatial resolved detection is possible, they suffer from disadvantages. Sensor properties like material degradation, poor measurement stability and a limited detection range circumvent routine clinical applications. Here we show the development and evaluation of radiation detectors based on gallium nitride (GaN) thin films. While previous publications revealed relative low energy absorption of GaN, it is possible to achieve very high signal amplification factors inside the material due to an appropriate sensor configuration, which, in turn, compensates the low energy absorption. Our devices, which have detection volumes smaller than 10{sup (}-6) cm{sup 3}, show a high sensitivity to X-ray intensity and can record the air kerma rate (free-in-air) range of 1 microgray/s to 10 mGy/s with a signal stability of 1% and a linear total dose response over time. The presented results show the potential of GaN-based thin films for dosimetry and imaging applications.

  10. Magneto-ballistic transport in GaN nanowires

    Santoruvo, Giovanni, E-mail:; Allain, Adrien; Ovchinnikov, Dmitry; Matioli, Elison, E-mail: [Ecole Polytechnique Fédérale de Lausanne (EPFL), CH 1015 Lausanne (Switzerland)


    The ballistic filtering property of nanoscale crosses was used to investigate the effect of perpendicular magnetic fields on the ballistic transport of electrons on wide band-gap GaN heterostructures. The straight scattering-less trajectory of electrons was modified by a perpendicular magnetic field which produced a strong non-linear behavior in the measured output voltage of the ballistic filters and allowed the observation of semi-classical and quantum effects, such as quenching of the Hall resistance and manifestation of the last plateau, in excellent agreement with the theoretical predictions. A large measured phase coherence length of 190 nm allowed the observation of universal quantum fluctuations and weak localization of electrons due to quantum interference up to ∼25 K. This work also reveals the prospect of wide band-gap GaN semiconductors as a platform for basic transport and quantum studies, whose properties allow the investigation of ballistic transport and quantum phenomena at much larger voltages and temperatures than in other semiconductors.

  11. Design and maskless fabrication of ultrathin suspended membranes of GaN

    Tiginyanu, I.M. [Institute of Electronic Engineering and Nanotechnologies, Academy of Sciences of Moldova, Chisinau (Moldova); National Center for Materials Study and Testing, Technical University of Moldova, Chisinau (Moldova); Popa, V. [National Center for Materials Study and Testing, Technical University of Moldova, Chisinau (Moldova); Stevens-Kalceff, M.A. [School of Physics, University of New South Wales, Sydney, NSW (Australia); Gerthsen, D.; Brenner, P. [Laboratory for Electron Microscopy, University of Karlsruhe (Germany); Pavlidis, D. [Institute of Electronics, Microelectronics and Nanotechnology, Cite Scientifique, Villeneuve d' Ascq Cedex (France)


    We report the maskless fabrication of ultrathin suspended GaN membranes designed by focused ion beam treatment of the GaN epilayer surface with subsequent photoelectrochemical etching. This technological approach allows the fabrication of ultrathin membranes, as well as supporting micro/nanocolumns in a controlled fashion. The analysis of the spatial and spectral distribution of microcathodoluminescence demonstrates that the membranes exhibit mainly yellow luminescence. These results pave the way for the fabrication of ultrathin suspended GaN membranes for MEMS/NEMS applications. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Stress and Defect Control in GaN Using Low Temperature Interlayers

    Akasaki, I.; Amano, H.; Chason, E.; Figiel, J.; Floro, J.A.; Han, J.; Hearne, S.; Iwaya, M.; Kashima, T.; Katsuragcawa, M.


    In organometallic vapor phase epitaxial growth of Gail on sapphire, the role of the low- temperature-deposited interlayers inserted between high-temperature-grown GaN layers was investigated by in situ stress measurement, X-ray diffraction, and transmission electron microscopy. Insertion of a series of low temperature GaN interlayers reduces the density of threading dislocations while simultaneously increasing the tensile stress during growth, ultimately resulting in cracking of the GaN film. Low temperature AIN interlayers were found to be effective in suppressing cracking by reducing tensile stress. The intedayer approach permits tailoring of the film stress to optimize film structure and properties.

  13. Synthesis and Photoluminescence of GaN Nanowires with Nb Catalyst

    ZHUANG Hui-zhao; LI Bao-li; XUE Cheng-shan; ZHANG Shi-ying; WANG De-xiao; SHEN Jia-bing


    Large-scale GaN nanowires are successfully synthesized by ammoniating Ga2O3 films on Nb layer deposited on Si(111) substrates at 850 ℃. X-ray diffraction(XRD), scanning electron microscopy(SEM), field-emssion transmission electron microscope(FETEM), Fourier transformed infrared spectrum(FTIR) are used to characterize the structural and morphological properties of the as-synthesized GaN nanowires. The results reveal that the nanowires are pure hexagonal GaN wurtzite structure with a length of about several microns and a diameter between 50 nm and 100 nm. Finally, discussed briefly is the formation mechanism of gallium nitride nanowires.

  14. Characterization of plasma etching damage on p -type GaN using Schottky diodes


    The plasma etching damage in p-type GaN has been characterized. From current-voltage and capacitance-voltage characteristics of Schottky diodes, it was revealed that inductively coupled plasma (ICP) etching causes an increase in series resistance of the Schottky diodes and compensation of acceptors in p-type GaN. We investigated deep levels near the valence band of p-type GaN using current deep level transient spectroscopy (DLTS), and no deep level originating from the ICP etching damage was ...

  15. Etching of GaN layers at electrolysis under UV-irradiation

    Zubenko, T. K.; Puzyk, M. V.; Stozharov, V. M.; Ermakov, I. A.; Kovalev, D. S.; Ivanova, S. A.; Usikov, A. S.; Medvedev, O. S.; Papchenko, B. P.; Kurin, S. Yu; Antipov, A. A.; Chernyakov, A. E.


    Etching of the GaN layers in 1M KOH aqua solution under irradiation was studied by the electro-stimulated photolysis using N2-laser (337 nm, 60 W/m2) as a light source. It was observed that the size and the depth of the failure monotonically depend on the optical power and the irradiation time of the N2 laser and the GaN layer type of conductivity. The GaN layers etching rate was evaluated. A mechanism of the failure in the n-GaN layers is discussed.

  16. Role of Stress Voltage on Structural Degradation of GaN High-Electron-Mobility Transistors


    GaN high-electron-mobility transistors ( HEMTs ) under high- voltage electrical stress degradation in the drain and gate current is electric field... GaN HEMTs after long-term DC and RF life tests at high voltage [12–16]. Crystallographic defects such as pits and cracks have been observed at the...created by high-voltage stress in GaN HEMTs . A complementary study of the evolution of these de- fects in the cross section as a function of stress

  17. An Octave Bandwidth, High PAE, Linear, Class J GaN High Power Amplifier


    versus the modeled small-signal gain and return loss response of the Class J amplifier using a 45-W CREE GaN HEMT . The amplifier has a gain of 13 to...AFFTC-PA-12055 An Octave Bandwidth, High PAE, Linear, Class J GaN High Power Amplifier Kris Skowronski, Steve Nelson, Rajesh Mongia, Howard...Technical Paper 3. DATES COVERED (From - To) 11/11 – 03/12 (etc.) 4. TITLE AND SUBTITLE An Octave Bandwidth, High PAE, Linear, Class J GaN High

  18. P-Type Doping of GaN by Mg+ Implantation

    YAO Shu-De; ZHAO Qiang; ZHOU Sheng-Qiang; YANG Zi-Jian; LU Yi-Hong; SUN Chang-Chun; SUN Chang; ZHANG Guo-Yi; VANTOMME Andre; PIPELEERS Bert


    Mg+ and Mg++P+ were introduced into GaN by ion implantation. The structure and crystalline quality of the GaN samples were analysed by Rutherford backscattering and channelling spectrometry before (xmin = 1.6%) and after implantation (Xmin = 4.1%). X-ray diffraction reveals the existence of implantation-induced damage in the case of post-implantation followed by rapid thermal annealing. The resistivity, average factor, carrier concentration and carrier mobility were measured by the Hall effect. The transformation from n-type to p-type for GaN was observed.

  19. Growth of Semi-Insulating GaN by Using Two-Step A1N Buffer Layer

    ZHOU Zhong-Tang; QUO Li-Wei; XING Zhi-Gang; DING Guo-Jian; ZHANG Jie; PENG Ming-Zeng; JIA Hai-Qiang; CHEN Hong; ZHOU Jun-Ming


    Semi-insulating GaN is grown by using a two-step A1N buffer layer by metalorganic chemical vapour deposition. The sheet resistance of as-grown semi-insulating GaN is dramatically increased to 1013 Ω/sq by using two-step A1N buffer instead of the traditional low-temperature GaN buffer. The high sheet resistance of as-grown GaN over 10 Ωfi/sq is due to inserting an insulating buffer layer (two-step A1N buffer) between the high-temperature GaN layer and a sapphire substrate which blocks diffusion of oxygen and overcomes the weakness of generating high density carrier near interface of GaN and sapphire when a low-temperature GaN buffer is used. The result suggests that the high conductive feature of unintentionally doped GaN is mainly contributed from the highly conductive channel near interface between GaN and the sapphire substrate, which is indirectly manifested by room-temperature photoluminescence excited by an incident laser beam radiating on growth surface and on the substrate. The functions of the two-step A1N buffer layer in reducing screw dislocation and improving crystal quality of GaN are also discussed.

  20. Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs.

    Shih, Huan-Yu; Shiojiri, Makoto; Chen, Ching-Hsiang; Yu, Sheng-Fu; Ko, Chung-Ting; Yang, Jer-Ren; Lin, Ray-Ming; Chen, Miin-Jang


    High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This "compliant" buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 10(5) cm(-2). In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6" wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors.

  1. Transparent, Flexible Piezoelectric Nanogenerator Based on GaN Membrane Using Electrochemical Lift-Off.

    Kang, Jin-Ho; Jeong, Dae Kyung; Ryu, Sang-Wan


    A transparent and flexible piezoelectric nanogenerator (TF PNG) is demonstrated based on a GaN membrane fabricated by electrochemical lift-off. Under shear stress on the TF PNG by finger force (∼182 mN), the GaN membrane effectively undergoes normal stress and generates piezoelectric polarization along the c-axis, resulting in the generation of piezoelectric output from the TF PNG. Although the GaN layer is 315 times thinner than the flexible polyethylene terephthalate (PET) substrate, the low Young's modulus of PET allows the GaN membranes to absorb ∼41% of the applied strain energy, which leads to their large lattice deformation under extremely low applied stress. Maximum output voltage and current values of 4.2 V and 150 nA are obtained, and the time decay of the output voltage is discussed.

  2. Modeling grown-in dislocation multiplication on prismatic slip planes for GaN single crystals

    Gao, B.; Kakimoto, K.


    To dynamically model the grown-in dislocation multiplication on prismatic slip planes for GaN single crystal growth, the Alexander-Haasen (AH) model, which was originally used to model the plastic deformation of silicon crystals, is extended to GaN single crystals. By fitting the model to the experimental data, we found that it can accurately describe the plastic deformation of GaN caused by prismatic slip. A set of unified parameters for the AH model at different temperatures can be found. This model provides a possible method to minimize grown-in dislocations caused due to prismatic slip by optimizing growing and cooling conditions during GaN single crystal growth.

  3. Role of lateral growth on the structural properties of high temperature GaN layer

    GAO ZhiYuan; HAO Yue; LI PeiXian; ZHANG JinCheng


    The role of lateral growth on the structural properties of high temperature (HT) GaN epitaxial layer has been investigated by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD).Variations of the lateral growth rate of HT GaN in metal-organic chemical vapor deposition (MOCVD)can be obtained by changing the Ⅴ/Ⅲ ratio. It is found that under higher lateral growth rate, dislocation is easier to bend into subgrains away from c axis, and the position where bend occurs is closer to the buffer layer, however, dislocation density does not show to monotonically vary with increasing lateral growth rate. A model concerning the GaN growth dynamics and dislocation bending mechanics has been proposed to explain the correlation between lateral growth and the structural properties of GaN.

  4. Formation of helical dislocations in ammonothermal GaN substrate by heat treatment

    Horibuchi, Kayo; Yamaguchi, Satoshi; Kimoto, Yasuji; Nishikawa, Koichi; Kachi, Tetsu


    GaN substrate produced by the basic ammonothermal method and an epitaxial layer on the substrate was evaluated using synchrotron radiation x-ray topography and transmission electron microscopy. We revealed that the threading dislocations present in the GaN substrate are deformed into helical dislocations and the generation of the voids by heat treatment in the substrate for the first observation in the GaN crystal. These phenomena are formed by the interactions between the dislocations and vacancies. The helical dislocation was formed in the substrate region, and not in the epitaxial layer region. Furthermore, the evaluation of the influence of the dislocations on the leakage current of Schottky barrier diodes fabricated on the epitaxial layer is discussed. The dislocations did not affect the leakage current characteristics of the epitaxial layer. Our results suggest that the deformation of dislocations in the GaN substrate does not adversely affect the epitaxial layer.

  5. High breakdown single-crystal GaN p-n diodes by molecular beam epitaxy

    Qi, Meng; Zhao, Yuning; Yan, Xiaodong; Li, Guowang; Verma, Jai; Fay, Patrick [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Nomoto, Kazuki; Zhu, Mingda; Hu, Zongyang; Protasenko, Vladimir; Song, Bo; Xing, Huili Grace; Jena, Debdeep, E-mail: [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Departments of ECE and MSE, Cornell University, Ithaca, New York 14853 (United States); Bader, Samuel [Departments of ECE and MSE, Cornell University, Ithaca, New York 14853 (United States)


    Molecular beam epitaxy grown GaN p-n vertical diodes are demonstrated on single-crystal GaN substrates. A low leakage current <3 nA/cm{sup 2} is obtained with reverse bias voltage up to −20 V. With a 400 nm thick n-drift region, an on-resistance of 0.23 mΩ cm{sup 2} is achieved, with a breakdown voltage corresponding to a peak electric field of ∼3.1 MV/cm in GaN. Single-crystal GaN substrates with very low dislocation densities enable the low leakage current and the high breakdown field in the diodes, showing significant potential for MBE growth to attain near-intrinsic performance when the density of dislocations is low.

  6. Theoretical study of Ni adsorption on the GaN(0 0 0 1) surface

    Gonzalez-Hernandez, Rafael, E-mail: [Grupo de Fisica de la Materia Condensada - GFMC, Departamento de Fisica, Universidad del Norte, Barranquilla (Colombia); GEMA - Grupo de Estudio de Materiales, Departamento de Fisica, Universidad Nacional de Colombia, Bogota (Colombia); Lopez, William [Grupo de Fisica de la Materia Condensada - GFMC, Departamento de Fisica, Universidad del Norte, Barranquilla (Colombia); Ortega, Cesar [Grupo Avanzado de Materiales y Sistemas Complejos - GAMASCO, Universidad de Cordoba, Monteria (Colombia); Moreno-Armenta, Maria Guadalupe [Centro de Nanociencias y Nanotecnologia de la UNAM, Ensenada, Baja California (Mexico); Arbey Rodriguez, Jairo [GEMA - Grupo de Estudio de Materiales, Departamento de Fisica, Universidad Nacional de Colombia, Bogota (Colombia)


    First-principles pseudo-potential calculations within density-functional theory framework are performed in order to study the structural and electronic properties of nickel adsorption and diffusion on a GaN(0 0 0 1)-2x2 surface. The adsorption energies and potential energy surfaces are investigated for a Ni adatom on the Ga-terminated (0 0 0 1) surface of GaN. This surface is also used to study the effect of the nickel surface coverage. The results show that the most stable positions of a Ni adatom on GaN(0 0 0 1) are at the H{sub 3} sites and T{sub 4} sites, for low and high Ni coverage respectively. In addition, confirming previous experimental results, we have found that the growth of Ni monolayers on the GaN(0 0 0 1) surface is possible.

  7. Efficient light extraction from GaN LEDs using gold-coated ZnO nanoparticles

    Alhadidi, A.


    We experimentally demonstrate the effect of depositing gold-coated ZnO nanoparticles on the surface of GaN multi-quantum well LED structures. We show that this method can significantly increase the amount of extracted light.

  8. Room-temperature ferromagnetism in V-doped GaN thin films grown by MOCVD

    Souissi, M.; El Jani, B. [Unite de Recherche sur les Hetero-Epitaxies et Applications, Faculte des Sciences de Monastir, 5000 Monastir (Tunisia); Schmerber, G.; Derory, A. [Institut de Physique et Chimie des Materiaux de Strasbourg (IPCMS), UMR7504 CNRS-UDS, 23 rue du Loess, BP 43, 67034 Strasbourg Cedex 2 (France)


    V-doped GaN thin films were grown on c-sapphire substrate by metal organic chemical vapour deposition method (MOCVD). We have used vanadium tetrachloride (VCl{sub 4}) to intentionally incorporate vanadium (V) during the crystal growth of GaN. X-ray diffraction measurements revealed no secondary phase in the samples. Magnetic experiments using superconducting quantum interference device (SQUID) showed clear hysteresis loop in magnetization versus applied field (M -H) curves for V-doped GaN films. The ferromagnetic behavior was evidenced at 300 K, implying the Curie temperature to be over 300 K. Strong and broad blue-luminescent band (centered at 2.6 eV) is induced by the V doping in GaN. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Preparation and characterization of GaN films grown on Ga-diffused Si(111) substrates

    SUN Zhencui; CAO Wentian; WEI Qinqin; WANG Shuyun; XUE Chengshan; SUN Haibo


    Hexagonal GaN films were prepared by nitriding Ga2O3 films with flowing ammonia. Ga2O3 films were deposited on Ga-diffused Si (111) substrates by radio frequency (r.f.) magnetron sputtering. This paper have investigated the change of structural properties of GaN films nitrided in NH3 atmosphere at the temperatures of 850, 900, and 950℃ for 15min and nitrided at the temperature of 900℃ for 10, 15, and 20 min, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to analyze the structure, surface morphology and composition of synthesized samples. The results reveal that the as-grown films are polycrystalline GaN with hexagonal wurtzite structure and GaN films with the highest crystal quality can be obtained when nitrided at 900℃ for 15 min.

  10. FIR Detectors/Cameras Based on GaN and Si Field-Effect Devices Project

    National Aeronautics and Space Administration — SETI proposes to develop GaN and Si based multicolor FIR/THz cameras with detector elements and readout, signal processing electronics integrated on a single chip....

  11. Spectroscopic investigation of native defect induced electron-phonon coupling in GaN nanowires

    Parida, Santanu; Patsha, Avinash; Bera, Santanu; Dhara, Sandip


    The integration of advanced optoelectronic properties in nanoscale devices of group III nitride can be realized by understanding the coupling of charge carriers with optical excitations in these nanostructures. The native defect induced electron-phonon coupling in GaN nanowires are reported using various spectroscopic studies. The GaN nanowires having different native defects are grown in an atmospheric pressure chemical vapor deposition technique. X-ray photoelectron spectroscopic analysis revealed the variation of Ga/N ratios in nanowires having possible native defects, with respect to their growth parameters. The analysis of the characteristic features of electron-phonon coupling in the Raman spectra show the variations in carrier density and mobility, with respect to the native defects in unintentionally doped GaN nanowires. The radiative recombination of donor acceptor pair transitions and the corresponding LO phonon replicas observed in photoluminescence studies further emphasize the role of native defects in electron-phonon coupling.

  12. Growth and Characterization of Semi-Insulating GaN Films Grown by MOCVD


    High resistivity unintentionally doped GaN films were grown on (0001) sapphire substrates by metalorganic chemical vapor deposition. The surface morphology of the layer was measured by both atomic force microscopy and scanning electron microscopy. The results show that the films have mirror-like surface morphology with root mean square of 0.3 nm. The full width at half maximum of double crystal X-ray diffraction rocking curve for (0002) GaN is about 5.22 arcmin, indicative of high crystal quality. The resistivity of the GaN epilayers at room temperature and at 250 ℃ was measured to be approximate 109 and 106 Ω·cm respectively, by variable temperature Hall measurement. Deep level traps in the GaN epilayers were investigated by thermally stimulated current and resistivity measurements.

  13. Research on fabrication and properties of nanoporous GaN epilayers

    WANG Xiaolong; YU Guanghui; WANG Xinzhong; LIN Chaotong; LEI Benliang; QI Ming; NOUET Gérard; RUTERANA Pierre; CHEN Jun


    Gallium nitride (GaN) epilayers with nanopore arrays were fabricated by inductive coupled plasma (ICP) etching using anodic aluminum oxide (AAO) as mask.Nanoporous AAO templates were formed by anodizing the Al films deposited on GaN epilayers.The diameter of the perforations in the AAO masks could be easily controlled by tuning the technique parameters of AAO fabrication process.Cl2/Ar and Cl2/He were employed as etching gas.Scanning electron microscopy (SEM) analysis shows that vertical nanoporous arrays with uniform distribution can directly be transferred from AAO masks to GaN films in some proper conditions.Photoluminescence (PL) spectra, X-ray diffraction (XRD) and Raman spectroscopy were applied to assess properties of the nanoporous GaN films with different average pore diameters and interpore distances.

  14. In situ studies of the effect of silicon on GaN growth modes.

    Munkholm, A.; Stephenson, G. B.; Eastman, J. A.; Auciello, O.; Murty, M. V. R.; Thompson, C.; Fini, P.; Speck, J. S.; DenBaars, S. P.; Northern Illinois Univ.; Univ. of California at Santa Barbara


    We present real-time X-ray scattering studies of the influence of silicon on the homoepitaxial growth mode of GaN grown by metal-organic vapor-phase epitaxy. Both annealing of Si-doped GaN and surface dosing of GaN with disilane are shown to change the mode of subsequent growth from step-flow to layer-by-layer. By comparing the growth behavior induced by doped layers which have been annealed to that induced by surface dosing, we extract an approximate diffusion coefficient for Si in GaN of 3.5 x 10{sup -18} cm{sup 2}/s at 810{sup o}C.

  15. Role of lateral growth on the structural properties of high temperature GaN layer


    The role of lateral growth on the structural properties of high temperature(HT) GaN epitaxial layer has been investigated by means of transmission electron microscopy(TEM) and X-ray diffraction(XRD).Variations of the lateral growth rate of HT GaN in metal-organic chemical vapor deposition(MOCVD) can be obtained by changing the V/Ⅲ ratio.It is found that under higher lateral growth rate,dislocation is easier to bend into subgrains away from c axis,and the position where bend occurs is closer to the buffer layer,however,dislocation density does not show to monotonically vary with increasing lateral growth rate.A model concerning the GaN growth dynamics and dislocation bending mechanics has been proposed to explain the correlation between lateral growth and the structural properties of GaN.

  16. Effects of Al additives on growth of GaN polycrystals by the Na flux method

    Imabayashi, Hiroki; Murakami, Kosuke; Matsuo, Daisuke; Honjo, Masatomo; Imanishi, Masayuki; Maruyama, Mihoko; Imade, Mamoru; Yoshimura, Masashi; Mori, Yusuke


    In this study, we investigated the growth of GaN polycrystals using the Al-added Na flux method. We studied the effects of Al on accelerating the nucleation and purity of GaN polycrystals. The yields of GaN crystals grown in Al-added Na flux were dramatically increased from those in Al-free Na flux, and the polycrystals grown by the Al-added Na flux method were highly transparent. As observed in secondary ion mass spectroscopy measurements, the Al content of the polycrystals was below the detection limit of 3 × 1016 atoms/cm3. From these results, the Al-added Na flux method is found to be appropriate for fabricating a large amount of GaN polycrystals without deteriorating the crystal quality.

  17. Step-Free GaN Hexagons Grown by Selective-Area Metalorganic Vapor Phase Epitaxy

    Akasaka, Tetsuya; Kobayashi, Yasuyuki; Kasu, Makoto


    Selective-area metalorganic vapor phase epitaxy of GaN has been investigated using the optimized growth conditions for the layer (Frank-van der Merwe) growth and GaN-template substrates with low dislocation density. The surface of a GaN hexagon with 16-µm diameter has a single wide terrace over almost the whole area (step-free surface), when there are no screw-type dislocations in the finite area. Step-free GaN hexagons grew in the two-dimensional nucleus growth mode and had approximately an eight times lower growth rate than that of a GaN film grown in the step-flow mode under the growth conditions used in this study.

  18. N-polar GaN epitaxy and high electron mobility transistors

    Hoi Wong, Man; Keller, Stacia; Nidhi; Dasgupta, Sansaptak; Denninghoff, Daniel J.; Kolluri, Seshadri; Brown, David F.; Lu, Jing; Fichtenbaum, Nicholas A.; Ahmadi, Elaheh; Singisetti, Uttam; Chini, Alessandro; Rajan, Siddharth; DenBaars, Steven P.; Speck, James S.; Mishra, Umesh K.


    This paper reviews the progress of N-polar (000\\mathop 1\\limits^\\_) GaN high frequency electronics that aims at addressing the device scaling challenges faced by GaN high electron mobility transistors (HEMTs) for radio-frequency and mixed-signal applications. Device quality (Al, In, Ga)N materials for N-polar heterostructures are developed using molecular beam epitaxy and metalorganic chemical vapor deposition. The principles of polarization engineering for designing N-polar HEMT structures will be outlined. The performance, scaling behavior and challenges of microwave power devices as well as highly-scaled depletion- and enhancement-mode devices employing advanced technologies including self-aligned processes, n+ (In,Ga)N ohmic contact regrowth and high aspect ratio T-gates will be discussed. Recent research results on integrating N-polar GaN with Si for prospective novel applications will also be summarized.

  19. LEDs on HVPE grown GaN substrates: Influence of macroscopic surface features

    SK. S. Rahman


    Full Text Available We demonstrate the strong influence of GaN substrate surface morphology on optical properties and performance of light emitting devices grown on freestanding GaN. As-grown freestanding HVPE GaN substrates show excellent AFM RMS and XRD FWHM values over the whole area, but distinctive features were observed on the surface, such as macro-pits, hillocks and facets extending over several millimeters. Electroluminescence measurements reveal a strong correlation of the performance and peak emission wavelength of LEDs with each of these observed surface features. This results in multiple peaks and non-uniform optical output power for LEDs on as-grown freestanding GaN substrates. Removal of these surface features by chemical mechanical polishing results in highly uniform peak wavelength and improved output power over the whole wafer area.

  20. Ivestigation of an InGaN - GaN nanowire heterstructure

    Limbach, Friederich; Gotschke, Tobias; Stoica, Toma; Calarco, Raffaella; Gruetzmacher, Detlev [Institute of Bio- and Nanosystems (IBN-1), Research Center Juelich GmbH, Juelich (Germany); JARA-Fundamentals of Future Information Technology, Juelich (Germany); Sutter, Eli; Ciston, Jim [Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY (United States); Cusco, Ramon; Artus, Luis [Institut Jaume Almera, Consell Superior d' Investigacions Cientifiques (CSIC), Barcelona, Catalonia (Spain); Kremling, Stefan; Hoefling, Sven; Worschech, Lukas [University Wurzburg, Wilhelm Conrad Rontgen Research Centre Complex Matter Systems, Wuerzburg (Germany)


    InGaN/GaN nanowire (NW) heterostructures grown by molecular beam epitaxy were studied in comparison to their GaN and InGaN counterparts. The InGaN/GaN heterostructure NWs are composed of a GaN NW, a thin InGaN shell, and a multi-faceted InGaN cap wrapping the top part of the GaN NW. Transmission electron microscopy images taken from different parts of a InGaN/GaN nanowire show a wurtzite structure of the GaN core and the epitaxial InGaN shell around it. Photoluminescence spectra of these heterostructure NW ensembles show an emission peak at 2.1 eV. However, {mu}-PL spectra measured on single nanowires reveal much sharper luminescence peaks. A Raman analysis reveals a variation of the In content between 20 % and 30 %, in agreement with PL and TEM investigations.

  1. Development of Epitaxial GaN Films for RF Communications Project

    National Aeronautics and Space Administration — The primary objective of this SBIR is to develop epitaxial GaN films with threading dislocation density less than 10^6 cm^-2. We propose an innovative approach...

  2. GaN nano-membrane for optoelectronic and electronic device applications

    Ooi, Boon S.


    The ~25nm thick threading dislocation free GaN nanomembrane was prepared using ultraviolet electroless chemical etching method offering the possibility of flexible integration of (Al,In,Ga)N optoelectronic and electronic devices.

  3. Droplet heteroepitaxy of zinc-blende vs. wurtzite GaN quantum dots

    Reese, C.; Jeon, S.; Hill, T.; Jones, C.; Shusterman, S.; Yacoby, Y.; Clarke, R.; Deng, H.; Goldman, Rs

    We have developed a GaN droplet heteroepitaxy process based upon plasma-assisted molecular-beam epitaxy. Using various surface treatments and Ga deposition parameters, we have demonstrated polycrystalline, zinc-blende (ZB), and wurtzite (WZ) GaN quantum dots (QDs) on Si(001), r-Al2O3, Si(111), and c-GaN substrates. For the polar substrates (i.e. Si(111) and c-GaN), high-resolution transmission electron microscopy and coherent Bragg rod analysis reveals the formation of coherent WZ GaN QDs with nitridation-temperature-dependent sizes and densities. For the non-polar substrates (i.e. Si(001) and r-Al2O3) , QDs with strong near-band photoluminescence emission are observed and ZB GaN QD growth on Si(001) is demonstrated for the first time.

  4. Surface chemistry and electronic structure of nonpolar and polar GaN films

    Mishra, Monu; Krishna, T.C. Shibin; Aggarwal, Neha; Gupta, Govind, E-mail:


    Highlights: • Surface chemistry and electronic structure of polar and nonpolar GaN is reported. • Influence of polarization on electron affinity of p & np GaN films is investigated. • Correlation between surface morphology and polarity has been deduced. - Abstract: Photoemission and microscopic analysis of nonpolar (a-GaN/r-Sapphire) and polar (c-GaN/c-Sapphire) epitaxial gallium nitride (GaN) films grown via RF-Molecular Beam Epitaxy is reported. The effect of polarization on surface properties like surface states, electronic structure, chemical bonding and morphology has been investigated and correlated. It was observed that polarization lead to shifts in core level (CL) as well as valence band (VB) spectra. Angle dependent X-ray Photoelectron Spectroscopic analysis revealed higher surface oxide in polar GaN film compared to nonpolar GaN film. On varying the take off angle (TOA) from 0° to 60°, the Ga−O/Ga−N ratio varied from 0.11–0.23 for nonpolar and 0.17–0.36 for polar GaN film. The nonpolar film exhibited N-face polarity while Ga-face polarity was perceived in polar GaN film due to the inherent polarization effect. Polarization charge compensated surface states were observed on the polar GaN film and resulted in downward band bending. Ultraviolet photoelectron spectroscopic measurements revealed electron affinity and ionization energy of 3.4 ± 0.1 eV and 6.8 ± 0.1 eV for nonpolar GaN film and 3.8 ± 0.1 eV and 7.2 ± 0.1 eV for polar GaN film respectively. Field Emission Scanning Electron Microscopy measurements divulged smooth morphology with pits on polar GaN film. The nonpolar film on the other hand showed pyramidal structures having facets all over the surface.

  5. High efficiency DC-DC converter using GaN transistors

    Tómaş, Cosmin-Andrei; Grecu, Cristian; Pantazicǎ, Mihaela; Marghescu, Ion


    The paper presents a new high-efficiency power switching supply using the Gallium Nitride (GaN) technology. There are compared two solutions, the first using standard MOS transistors and the second using the new GaN transistor. The actual green technologies for obtaining the maximum energy and minimum losses have pushed the semiconductor industry into a continuous research regarding high power and high frequency devices, having uses in both digital communications and switching power supplies.

  6. The Effect of Atomic Vacancies and Grain Boundaries on Mechanical Properties of GaN Nanowires

    XIE Shi-Feng; CHEN Shang-Da; SOS Ai-Kah


    @@ Molecular dynamics simulations are carried out to investigate the influences of various defects on mechanical properties of wurtzite GaN nanowires by adopting the empirical Stillinger-Weber potential.Different types of vacancies and grain boundaries are considered and the uniaxial loading condition is implemented along the [001] direction.It is found that surface defects have less impact on Voung's moduli and critical stresses of GaN nanowires compared with random defects.The grain boundary normal to the axial direction of a nanowire would not significantly affect Young's moduli of nanowires.However, the inversion domain grain boundaries with and without wrong bonds would significantly lower Young's moduli of GaN nanowires.In addition, the inversion domain grain boundary affects the critical stress of GaN nanowires more than the grain boundary with interface normal to the axial direction of the nanowire.%Molecular dynamics simulations are carried out to investigate the influences of various defects on mechanical properties of wurtzite GaN nanowires by adopting the empirical Stillinger-Weber potential. Different types of vacancies and grain boundaries are considered and the uniaxial loading condition is implemented along the [001] direction. It is found that surface defects have less impact on Young's moduli and critical stresses of GaN nanowires compared with random defects. The grain boundary normal to the axial direction of a nanowire would not significantly affect Young's moduli of nanowires. However, the inversion domain grain boundaries with and without wrong bonds would significantly lower Young's moduli of GaN nanowires. In addition, the inversion domain grain boundary affects the critical stress of GaN nanowires more than the grain boundary with interface normal to the axial direction of the nanowire.

  7. A comparative DFT study of the structural and electronic properties of nonpolar GaN surfaces

    González-Hernández, Rafael, E-mail: [Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla (Colombia); González-García, Alvaro [Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla (Colombia); Barragán-Yani, Daniel [Fachgebiet Material modellierung, Institut für Materialwissenschaft, Technische Universität Darmstadt, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); López-Pérez, William [Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla (Colombia)


    Highlights: • A comparative analysis of the geometry and the electronic characteristics of nonpolar GaN surfaces was carried out. • Surface energies are too low for LDA, but lower still for GGA and MGGA functionals, except for PBEsol. • PBEsol exhibits good lattice parameters and surface energies. • Surface intra-gap states reduce the band gap of the nonpolar GaN surfaces. • Slight changes in the dispersion of surface states were observed for the LDA, GGA, and MGGA functionals. - Abstract: A comparative analysis of the geometry and the electronic characteristics of nonpolar GaN surfaces was carried out using density-functional theory (DFT) with different approximations for the exchange-correlation energy (LDA, PBE, PBEsol, RPBE, TPSS, revTPSS, and HSE). The obtained data show that the GaN(101{sup ¯}0) (m-plane) is more energetically stable than the GaN(112{sup ¯}0) (a-plane) surface. However, these surfaces have similar surface relaxation geometry, with a Ga-N surface bond-length contraction of around 6–7% and a Ga-N surface rotational angle in the range of 6–9°. Our results show that the use of different exchange-correlation functionals does not significantly change the surface energy and surface geometry. In addition, we found the presence of surface intra-gap states that reduce the band gap of the nonpolar GaN surface with respect to the bulk value, in agreement with recent photoelectron and surface optical spectroscopy experiments.

  8. Layer-by-layer growth of GaN induced by silicon

    Munkholm, A. [Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Thompson, Carol [Department of Physics, Northern Illinois University, DeKalb, Illinois 60115 (United States); Ramana Murty, M. V. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Eastman, J. A. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Auciello, O. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Stephenson, G. B. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Fini, P. [Materials Department, University of California, Santa Barbara, California 93106 (United States); DenBaars, S. P. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Speck, J. S. [Materials Department, University of California, Santa Barbara, California 93106 (United States)


    We present in situ x-ray scattering studies of surface morphology evolution during metal-organic chemical vapor deposition of GaN. Dosing the GaN(0001) surface with Si is shown to change the growth mode from step-flow to layer-by-layer over a wide temperature range. Annealing of highly doped layers causes Si to segregate to the surface, which also induces layer-by-layer growth. (c) 2000 American Institute of Physics.

  9. Effects of Mg Doping on Photoconductivity of GaN Films

    Deheng ZHANG; Qingpu WANG; Yunyan LIU


    This paper presents the UV photoconductivity properties of GaN films doped with different Mg concentrations deposited by MOCVD. It was observed that for the undoped and weakly doped GaN films the UV photocurrent response was relatively large and the relax time was relatively short. With an increase in doped Mg content, the samples became p-type, the photocurrent response became weak and the relax time became longer.

  10. The dispersion of BED ° in unintentional doped GaN crystals

    Qingcheng, Bao; Fungleng, Zhang; Ke, Shi; Rensong, Dai; Xurong, Xu


    The polarization and the wavelength of the photoluminescence of BED ° in not intentionaly doped GaN crystal wafers are observed to be dependent on the excitation intensity (I-exc). When I-exc increases from 1 KW/CM 2 to 1000 KW/CM 2, they vary at first quadratically, and then, appear saturated. This phenomenon is resulted from dispersion effect of BED ° in GaN crystal wafers, which is proposed earlier (1).

  11. Antioxidant Formulae, Shengmai San, and LingGuiZhuGanTang, Prevent MPTP Induced Brain Dysfunction and Oxidative Damage in Mice


    The present study was designed to evaluate the preventive effect of antioxidative traditional oriental medicine formulae, Shengmai San (SMS) and LingGuiZhuGanTang (LGZGT), against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (i.p 30 mg·kg−1 for 5 consecutive days) induced neurotoxicity. In in vitro antioxidant assays measured with Trolox and butyl hydroxyl toluene as reference antioxidant revealed that SMS has higher scavenging potential against hydroxyl radical than superoxide anion r...

  12. Real time spectroscopic ellipsometry investigation of homoepitaxial GaN grown by plasma assisted molecular beam epitaxy

    Kim, Tong-Ho; Choi, Soojeong; Wu, Pae; Brown, April [Department of Electrical and Computer Engineering, Duke University, 128 Hudson Hall, Durham, NC (United States); Losurdo, Maria; Giangregorio, Maria M.; Bruno, Giovanni [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM UdR Bari, via Orabona, 4, 70126 Bari (Italy); Moto, Akihiro [Innovation Core SEI, Inc., 3235 Kifer Road, Santa Clara, CA 95051 (United States)


    The growth of GaN by plasma assisted molecular beam epitaxy on GaN template substrates (GaN on sapphire) is investigated with in-situ multi-channel spectroscopic ellipsometry. Growth is performed under various Ga/N flux ratios at growth temperatures in the range 710-780 C. The thermal roughening of the GaN template caused by decomposition of the surface is investigated through the temporal variation of the GaN pseudodielectric function over the temperature range of 650 C to 850 C. The structural, morphological, and optical properties are also discussed. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Comparison of Electronic and Optical Properties of GaN Monolayer and Bulk Structure: a First Principle Study

    Imran, Muhammad; Hussain, Fayyaz; Rashid, Muhammad; Ullah, Hafeez; Sattar, Atif; Iqbal, Faisal; Ahmad, Ejaz


    The semiconducting two-dimensional (2D) architectures materials have potential applications in electronics and optics. The design and search of new 2D materials have attracted extensive attention recently. In this study, first principle calculation has been done on 2D gallium nitride (GaN) monolayer with respect to its formation and binding energies. The electronic and optical properties are also investigated. It is found that the single isolated GaN sheet is forming mainly ionic GaN bonds despite a slightly weaker GaN interaction as compared with its bulk counterpart. The dielectric constant value of 2D GaN is smaller as compared to 3D GaN due to less effective electronic screening effect in the layer, which is accompanied by lesser optical adsorption range and suggested to be a promising candidate in electronic and optoelectronic devices.

  14. Evolution of threading dislocations in GaN epitaxial laterally overgrown on GaN templates using self-organized graphene as a nano-mask

    Xu, Yu; Cao, Bing; He, Shunyu; Qi, Lin; Li, Zongyao; Cai, Demin; Zhang, Yumin; Ren, Guoqiang; Wang, Jianfeng; Wang, Chinhua; Xu, Ke


    Growth of high-quality GaN within a limited thickness is still a challenge, which is important both in improving device performance and in reducing the cost. In this work, a self-organized graphene is investigated as a nano-mask for two-step GaN epitaxial lateral overgrowth (2S-ELOG) in hydride vapor phase epitaxy. Efficient improvement of crystal quality was revealed by x-ray diffraction. The microstructural properties, especially the evolution of threading dislocations (TDs), were investigated by scanning electron microscopy and transmission electron microscopy. Stacking faults blocked the propagation of TDs, and fewer new TDs were subsequently generated by the coalescence of different orientational domains and lateral-overgrown GaN. This evolution mechanism of TDs was different from that of traditional ELOG technology or one-step ELOG (1S-ELOG) technology using a two-dimensional (2D) material as a mask.

  15. Improved performance of GaN metal-semiconductor-metal ultraviolet detectors by depositing SiO2 nanoparticles on a GaN surface

    Sun, Xiaojuan; Li, Dabing; Jiang, Hong; Li, Zhiming; Song, Hang; Chen, Yiren; Miao, Guoqing


    GaN metal-semiconductor-metal (MSM) ultraviolet detectors were investigated by depositing different density of SiO2 nanoparticles (SNPs) on the GaN. It was shown that the dark current of the detectors with SNPs was more than one order of magnitude lower than that without SNPs and the peak responsivity was enhanced after deposition of the SNPs. Atomic force microscopy observations indicated that the SNPs usually formed at the termination of screw and mixed dislocations, and further current-voltage measurements showed that the leakage of the Schottky contact for the GaN MSM detector decreased with deposited the SNPs. Moreover, the leakage obeyed the Frenkel-Poole emission model, which meant that the mechanism for improving the performance is the SNPs passivation of the dislocations followed by the reduction in the dark current.

  16. A preliminary description of the Gan-Hang failed rift, southeastern china

    Goodell, P. C.; Gilder, S.; Fang, X.


    The Gan-Hang failed rift, as defined by present-day topography, extends at least 450 km in length and 50 km in width. It is a northeast-southwest trending series of features spanning from Hangzhou Bay in Zhejiang province into Jiangxi province through Fuzhou City. Southwest of Fuzhou, the rift splits into two portions: one continuing along the southwestern trend, and the other diverging westward. The total extent of the rift cannot be defined at this time. The rift is superimposed upon a major suture zone of Caledonian or early Mesozoic age. The suture represents the fusing of the South China (Huanan) and Yangtze cratons. Perhaps in Late Triassic, but for sure by Late-Middle Jurassic time, the rifting was initiated and followed this older suture, in part. This time corresponds roughly to the middle stage of the Yanshanian orogeny and to the subduction of the postulated Pacific- Kula ridge southeast of the continental margin. The total thickness of the sediments and volcanics filling the rift valley reaches more than 10,000 m. Peak intensity of extension was between Late-Middle Jurassic and Middle to Late Cretaceous. Sedimentation within the rift was not continuous and is marked with periodic unconformities. Sediments within the rift include red beds, sandstones, siltstones, mudstones, conglomerates, breccias, tuffs, and ignimbrites. Vertebrate fossils and dinosaur eggs are also found. Contemporaneous volcanics within and flanking the rift include basalts, rhyolites, granites, gabbros, dacites, and andesites. Silicic volcanics are mostly attributed to caldera systems. Early basalts are tholeiitic and later change to alkaline-olivine basalt. Bimodal volcanism is recognized. Peak intensity of volcanism ranges between 135 and 75 Ma. In Early Cenozoic time, the area was a topographic low. Paleocene- Eocene sediments and evaporites are the last rocks to be deposited in the rift. Today the rift is delineated by major, high-angle faults (the Pingxiang-Guangfeng deep fault

  17. Hybrid device based on GaN nanoneedles and MEH-PPV/PEDOT:PSS polymer

    Shin, Min Jeong; Gwon, Dong-Oh; Lee, Chan-Mi; Lee, Gang Seok [Department of Applied Science, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Jeon, In-Jun [Department of Nano-semiconductor Engineering, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Ahn, Hyung Soo [Department of Applied Science, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Department of Nano-semiconductor Engineering, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Yi, Sam Nyung, E-mail: [Department of Applied Science, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Department of Nano-semiconductor Engineering, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Ha, Dong Han [Division of Convergence Technology, Korea Research Institute of Standards and Science, Daejeon 305-340 (Korea, Republic of)


    Highlights: • A hybrid device was demonstrated by using MEH-PPV, PEDOT:PSS, and GaN nanoneedles. • I–V curve of the hybrid device showed its rectification behaviour, similar to a diode. • EL peak originated by the different potential barriers at MEH-PPV and GaN interface. - Abstract: A hybrid device that combines the properties of organic and inorganic semiconductors was fabricated and studied. It incorporated poly[2-methoxy-5-(2-ethylhexyloxy)- 1,4-phenylenevinylene] (MEH-PPV) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as organic polymers and GaN nanoneedles as an inorganic semiconductor. Layers of the two polymers were spin coated on to the GaN nanoneedles. The one peak in the electroluminescence spectrum originated from the MEH-PPV layer owing to the different potential barriers of electrons and holes at its interface with the GaN nanoneedles. However, the photoluminescence spectrum showed peaks due to both GaN nanoneedles and MEH-PPV. Such hybrid structures, suitably developed, might be able to improve the efficiency of optoelectronic devices.

  18. Strain-induced step bunching in orientation-controlled GaN on Si

    Narita, Tetsuo; Iguchi, Hiroko; Horibuchi, Kayo; Otake, Nobuyuki; Hoshi, Shinichi; Tomita, Kazuyoshi


    We report a technique for the fabrication of high-quality GaN-on-silicon (Si) substrates for use in various power applications. GaN epitaxial layers were generated on Si(111) vicinal faces that had been previously covered with a thin coating of Al2O3 to control the orientation of the AlN seed layers. We obtained orientation-controlled GaN layers and found a linear relationship between the GaN c-axis and Si[111] tilt angles. As a result, the threading dislocation density in the AlN seed layer was reduced and high-quality GaN layers were generated. The X-ray rocking curves for these layers exhibited full width at half maximum values of 390‧‧ and 550‧‧ for the (004) and (114) reflections, respectively. Significant step bunching was observed on a GaN(0001) vicinal face produced using this technique, attributed to strain-induced attractive interactions between steps. Thus, by controlling the strain near the surface layer, we achieved the step flow growth of GaN on Si.

  19. Carbon nanotube assisted Lift off of GaN layers on sapphire

    Long, Hao; Feng, Xiaohui; Wei, Yang; Yu, Tongjun; Fan, Shoushan; Ying, Leiying; Zhang, Baoping


    Laser lift off (LLO) was one of the most essential processes in fabrication of vertical GaN-based LEDs. However, traditional laser lift off of GaN on sapphire substrates needed high laser energy threshold, which deteriorated the GaN crystal. In this paper, it was found that inserting carbon nanotube between GaN and sapphire could effectively reduce the laser energy threshold in GaN LLO, from 1.5 J /cm2 of conventional GaN/sapphire to 1.3 J /cm2 of CNT inserted GaN/sapphire. The temperature distributions at the GaN/sapphire interfaces with and without CNTs were simulated by the finite elements calculation under laser irradiation. It was found that, due to the higher laser absorption coefficient of CNT, the CNT played as a powerful heating wire, sending out the thermal outside to elevate the GaN's temperature, and thus reduce the laser threshold for LLO. Raman and photoluminescence measurements indicated that residual stress of GaN membranes was as small as 0.3 GPa by the carbon nanotube assisted LLO. This work not only opens new application of CNTs, but also demonstrates the potential of high performance blue and green LEDs.

  20. Fabrication and characterization of GaN nanowire doubly clamped resonators

    Maliakkal, Carina B., E-mail:; Mathew, John P.; Hatui, Nirupam; Rahman, A. Azizur; Deshmukh, Mandar M.; Bhattacharya, Arnab [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005 (India)


    Gallium nitride (GaN) nanowires (NWs) have been intensely researched as building blocks for nanoscale electronic and photonic device applications; however, the mechanical properties of GaN nanostructures have not been explored in detail. The rigidity, thermal stability, and piezoelectric properties of GaN make it an interesting candidate for nano-electromechanical systems. We have fabricated doubly clamped GaN NW electromechanical resonators on sapphire using electron beam lithography and estimated the Young's modulus of GaN from resonance frequency measurements. For wires of triangular cross section with side ∼90 nm, we obtained values for the Young's modulus to be about 218 and 691 GPa, which are of the same order of magnitude as the values reported for bulk GaN. We also discuss the role of residual strain in the nanowire on the resonant frequency and the orientation dependence of the Young's modulus in wurtzite crystals.

  1. From Stable ZnO and GaN Clusters to Novel Double Bubbles and Frameworks

    Matthew R. Farrow


    Full Text Available A bottom up approach is employed in the design of novel materials: first, gas-phase “double bubble” clusters are constructed from high symmetry, Th, 24 and 96 atom, single bubbles of ZnO and GaN. These are used to construct bulk frameworks. Upon geometry optimization—minimisation of energies and forces computed using density functional theory—the symmetry of the double bubble clusters is reduced to either C1 or C2, and the average bond lengths for the outer bubbles are 1.9 Å, whereas the average bonds for the inner bubble are larger for ZnO than for GaN; 2.0 Å and 1.9 Å, respectively. A careful analysis of the bond distributions reveals that the inter-bubble bonds are bi-modal, and that there is a greater distortion for ZnO. Similar bond distributions are found for the corresponding frameworks. The distortion of the ZnO double bubble is found to be related to the increased flexibility of the outer bubble when composed of ZnO rather than GaN, which is reflected in their bulk moduli. The energetics suggest that (ZnO12@(GaN48 is more stable both in gas phase and bulk frameworks than (ZnO12@(ZnO48 and (GaN12@(GaN48. Formation enthalpies are similar to those found for carbon fullerenes.

  2. Synthesis of GaN Nanorods by a Solid-State Reaction

    Keyan Bao


    Full Text Available An atom-economical and eco-friendly chemical synthetic route was developed to synthesize wurtzite GaN nanorods by the reaction of NaNH2 and the as-synthesized orthorhombic GaOOH nanorods in a stainless steel autoclave at 600∘C. The lengths of the GaN nanorods are in the range of 400–600 nm and the diameters are about 80–150 nm. The process of orthorhombic GaOOH nanorods transformation into wurtzite GaN nanorods was investigated by powder X-ray diffraction (XRD and field emission scanning electron microscope (FESEM, indicating that the GaN product retained essentially the same basic topological morphology in contrast to that of the GaOOH precursor. It was found that rhombohedral Ga2O3 was the intermediate between the starting orthorhombic GaOOH precursor and the final wurtzite GaN product. The photoluminescence measurements reveal that the as-prepared wurtzite GaN nanorods showed strong blue emission.

  3. Enhanced water splitting with silver decorated GaN photoelectrode

    Hou, Y.; Syed, Z. A.; Smith, R.; Athanasiou, M.; Gong, Y.; Yu, X.; Bai, J.; Wang, T.


    By means of a cost-effective approach, we demonstrate a GaN-based photoelectrode decorated with self-organized silver nano-islands employed for solar powered hydrogen generation, demonstrating 4 times increase in photocurrent compared with a reference sample without using any silver. Our photoelectrode exhibits a 60% incident photon-to-electron conversion efficiency. The enhanced hydrogen generation is attributed to a significantly increased carrier generation rate as a result of strongly localized electric fields induced by surface plasmon coupling effect. The silver coating also contributes to the good chemical stability of our photoelectrode in a strong alkali electrolyte. This work paves the way for the development of GaN and also InGaN based photoelectrodes with ultra-high solar hydrogen conversion efficiency.

  4. 5 Watt GaN HEMT Power Amplifier for LTE

    K. Niotaki


    Full Text Available This work presents the design and implementation of a stand-alone linear power amplifier at 2.4 GHz with high output power. A GaN HEMT transistor is selected for the design and implementation of the power amplifier. The device exhibits a gain of 11.7 dB and a drain efficiency of 39% for an output power of 36.7 dBm at 2.4 GHz for an input power of 25dBm. The carrier to intermodulation ratio is better than 25 dB for a two tone input signal of 25 dBm of total power and a spacing of 5 MHz. The fabricated device is also tested with LTE input signals of different bandwidths (5MHz to 20MHz.

  5. GaN Metal Oxide Semiconductor Field Effect Transistors

    Ren, F.; Pearton, S.J.; Abernathy, C.R.; Baca, A.; Cheng, P.; Shul, R.J.; Chu, S.N.G.; Hong, M.; Lothian, J.R.; Schurman, M.J.


    A GaN based depletion mode metal oxide semiconductor field effect transistor (MOSFET) was demonstrated using Ga{sub 2}O{sub 3}(Gd{sub 2}O{sub 3}) as the gate dielectric. The MOS gate reverse breakdown voltage was > 35V which was significantly improved from 17V of Pt Schottky gate on the same material. A maximum extrinsic transconductance of 15 mS/mm was obtained at V{sub ds} = 30 V and device performance was limited by the contact resistance. A unity current gain cut-off frequency, f{sub {tau}}, and maximum frequency of oscillation, f{sub max} of 3.1 and 10.3 GHz, respectively, were measured at V{sub ds} = 25 V and V{sub gs} = {minus}20 V.

  6. Microstructure of laterally overgrown GaN layers

    Liliental-Weber, Zuzanna; Cherns, David


    Transmission electron microscopy study of plan-view and cross-section samples of epitaxial laterally overgrown (ELOG) GaN samples is described. Two types of dislocation with the same type of Burgers vector but different line direction have been observed. It is shown that threading edge dislocations bend to form dislocation segments in the c-plane as a result of shear stresses developed in the wing material along the stripe direction. It is shown that migration of these dislocations involves both glide and climb. Propagation of threading parts over the wing area is an indication of high density of point defects present in the wing areas on the ELOG samples. This finding might shed new light on the optical properties of such samples.

  7. ``A Minority View'' Gian-Carlo Rota's Phenomenological Realism

    Palombi, Fabrizio

    In 1997 Rota's second anthology was published, entitled Indiscrete Thoughts. The theses put forward in the book were "minority" positions in a Unites States cultural context that, after long having attempted to replace philosophy with logical analysis and the analysis of language (Hersh, 1997, pp. IX-X), was preparing to interpret it also in neuroscientific terms. Rota intended to show that he did not fear uncomfortable positions and chose the phrase "a minority view" as a provocative title for the philosophy section of the book, inspired by phenomenology. We cannot understand the importance of Rota's intellectual figure, within the American cultural context of the end of the twentieth century, and the importance of his heritage if we interpret it in terms of architectonic of philosophy.

  8. Monte Carlo Evaluation of Tritium Beta Spectrum Energy Deposition in Gallium Nitride (GaN) Direct Energy Conversion Devices


    Monte Carlo Evaluation of Tritium Beta Spectrum Energy Deposition in Gallium Nitride (GaN) Direct Energy Conversion Devices by Marc Litz...MD 20783-1138 ARL-TR-7082 September 2014 Monte Carlo Evaluation of Tritium Beta Spectrum Energy Deposition in Gallium Nitride (GaN... Tritium Beta Spectrum Energy Deposition in Gallium Nitride (GaN) Direct Energy Conversion Devices 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM

  9. Status of Structural Analysis of Substrates and Film Growth Inputs for GaN Device Development Program


    from 8 scans per 2” sample to 32. Our team has been developing GaN Schottky diodes and HEMTs with segments of these wafers. 12 Figure 7. Ranking...analysis of variance Asym asymmetric x-ray scan CL cathodoluminescence FOM figure of merit FWHM full width at half maximum GaN gallium nitride HEMT ...Status of Structural Analysis of Substrates and Film Growth Inputs for GaN Device Development Program by Kevin Kirchner ARL-TR-5427

  10. Design of a new two-dimensional diluted magnetic semiconductor: Mn-doped GaN monolayer

    Zhao, Qian; Xiong, Zhihua; Luo, Lan; Sun, Zhenhui; Qin, Zhenzhen; Chen, Lanli; Wu, Ning


    To meet the need of low-dimensional spintronic devices, we investigate the electronic structure and magnetic properties of Mn-doped GaN monolayer using first-principles method. We find the nonmagnetic GaN monolayer exhibits half-metallic ferromagnetism by Mn doping due to double-exchange mechanism. Interestingly, the ferromagnetic coupling in Mn-doped GaN monolayer is enhanced with tensile strain and weakened with compressive strain. What is more, the ferromagnetic-antiferromagnetic transformation occurs under compressive strain of -9.5%. These results provide a feasible approach for fabrication of a new GaN monolayer based diluted magnetic semiconductor.

  11. An investigation of structural properties of GaN films grown on patterned sapphire substrates by MOVPE

    Törmä, P. T.; Ali, M.; Svensk, O.; Sintonen, S.; Kostamo, P.; Suihkonen, S.; Sopanen, M.; Lipsanen, H.; Odnoblyudov, M. A.; Bougrov, V. E.


    GaN films were fabricated by metal organic vapor phase epitaxy (MOVPE) on patterned sapphire substrates (PSSs) with either direct or inverse type patterned structures. Both of these two types of PSSs had their own unique GaN growth process which depart from the standard growth on the planar c-plane. GaN films on PSSs showed decreased threading dislocation (TD) density. However, differences between the crystal quality of the GaN films grown on PSSs were observed. It was also found out with one of the pattern type that the TD density varied laterally and followed the periodicity of the pattern on the sapphire surface.

  12. High-resistivity GaN buffer templates and their optimization for GaN-based HFETs

    Hubbard, S. M.; Zhao, G.; Pavlidis, D.; Sutton, W.; Cho, E.


    High-resistance (HR) GaN templates for AlGaN/GaN heterojunction field effect transistor (HFET) applications were grown using organometallic vapor phase epitaxy. The GaN sheet resistance was tuned using final nucleation layer (NL) annealing temperature and NL thickness. Using an annealing temperature of 1033 °C and NL thickness of 26 nm, GaN with sheet resistance of 10 10 Ω/sq was achieved, comparable to that of Fe-doped GaN. Material characterization results show that the high-resistance GaN is achieved due to compensating acceptor levels that may be introduced through edge-type threading dislocations. Optimization of annealing temperature and NL thickness provided a means to maximize GaN sheet resistance without significantly degrading material quality. In situ laser reflectance was used to correlate the NL properties to sheet resistance and material quality, providing a figure of merit for expected sheet resistance. AlGaN/GaN HFET layers grown using HR GaN templates with R of 10 10 Ω/sq gave surface and interface roughness of 14 and 7 Å, respectively. The 2DEG Hall mobility and sheet charge of HFETs grown using HR GaN templates was comparable to similar layers grown using unintentionally doped (UID) GaN templates.

  13. Stress Control in GaN Grown on 6H-SiC by Metalorganic Chemical Vapor Deposition

    CHEN Yao; JIANG Yang; XU Pei-Qiang; MA Zi-Guang; WANG Xiao-Li; WANG Lu; JIA Hai-Qiang; CHEN Hong


    The strain in GaN epitaxial layers grown on 6H-SiC substrates with an AIN buffer by metalorganic chemical wpor deposition is investigated.It is found that the insertion of a graded AlGaN layer between the GaN layer and the AIN buffer can change the signs of strain.A compressive strain in an overgrown thick (2 μm) GaN layer is obtained.High-resolution x-ray diffraction, Raman spectroscopy and photoluminescence measurements are used to determine the strain state in the GaN layers.The mechanism of stress control by inserting graded AlGaN in subsequent GaN layers is discussed briefly.%@@ The strain in GaN epitaxial layers grown on 611-SiC substrates with an AIN buffer by metalorganic chemical vapor deposition is investigated.It is found that the insertion of a graded AlGaN layer between the GaN layer and the AIN buffer can change the signs of strain.A compressive strain in an overgrown thick(2μm)GaN layer is obtained.High-resolution x-ray diffraction, Raman spectroscopy and photoluminescence measurements are used to determine the strain state in the GaN layers.The mechanism of stress control by inserting graded AlGaN in subsequent GaN layers is discussed briefly.

  14. High active nitrogen flux growth of GaN by plasma assisted molecular beam epitaxy

    McSkimming, Brian M., E-mail:; Speck, James S. [Materials Department, University of California, Santa Barbara, California 93106-5050 (United States); Chaix, Catherine [RIBER S.A., 3a Rue Casimir Périer, BP 70083, 95873 Bezons Cedex (France)


    In the present study, the authors report on a modified Riber radio frequency (RF) nitrogen plasma source that provides active nitrogen fluxes more than 30 times higher than those commonly used for plasma assisted molecular beam epitaxy (PAMBE) growth of gallium nitride (GaN) and thus a significantly higher growth rate than has been previously reported. GaN films were grown using N{sub 2} gas flow rates between 5 and 25 sccm while varying the plasma source's RF forward power from 200 to 600 W. The highest growth rate, and therefore the highest active nitrogen flux, achieved was ∼7.6 μm/h. For optimized growth conditions, the surfaces displayed a clear step-terrace structure with an average RMS roughness (3 × 3 μm) on the order of 1 nm. Secondary ion mass spectroscopy impurity analysis demonstrates oxygen and hydrogen incorporation of 1 × 10{sup 16} and ∼5 × 10{sup 17}, respectively. In addition, the authors have achieved PAMBE growth of GaN at a substrate temperature more than 150 °C greater than our standard Ga rich GaN growth regime and ∼100 °C greater than any previously reported PAMBE growth of GaN. This growth temperature corresponds to GaN decomposition in vacuum of more than 20 nm/min; a regime previously unattainable with conventional nitrogen plasma sources. Arrhenius analysis of the decomposition rate shows that samples with a flux ratio below stoichiometry have an activation energy greater than decomposition of GaN in vacuum while samples grown at or above stoichiometry have decreased activation energy. The activation energy of decomposition for GaN in vacuum was previously determined to be ∼3.1 eV. For a Ga/N flux ratio of ∼1.5, this activation energy was found to be ∼2.8 eV, while for a Ga/N flux ratio of ∼0.5, it was found to be ∼7.9 eV.

  15. Piezo-generator integrating a vertical array of GaN nanowires.

    Jamond, N; Chrétien, P; Houzé, F; Lu, L; Largeau, L; Maugain, O; Travers, L; Harmand, J C; Glas, F; Lefeuvre, E; Tchernycheva, M; Gogneau, N


    We demonstrate the first piezo-generator integrating a vertical array of GaN nanowires (NWs). We perform a systematic multi-scale analysis, going from single wire properties to macroscopic device fabrication and characterization, which allows us to establish for GaN NWs the relationship between the material properties and the piezo-generation, and to propose an efficient piezo-generator design. The piezo-conversion of individual MBE-grown p-doped GaN NWs in a dense array is assessed by atomic force microscopy (AFM) equipped with a Resiscope module yielding an average output voltage of 228 ± 120 mV and a maximum value of 350 mV generated per NW. In the case of p-doped GaN NWs, the piezo-generation is achieved when a positive piezo-potential is created inside the nanostructures, i.e. when the NWs are submitted to compressive deformation. The understanding of the piezo-generation mechanism in our GaN NWs, gained from AFM analyses, is applied to design a piezo-generator operated under compressive strain. The device consists of NW arrays of several square millimeters in size embedded into spin-on glass with a Schottky contact for rectification and collection of piezo-generated carriers. The generator delivers a maximum power density of ∼12.7 mW cm(-3). This value sets the new state of the art for piezo-generators based on GaN NWs and more generally on nitride NWs, and offers promising prospects for the use of GaN NWs as high-efficiency ultra-compact energy harvesters.

  16. GaN Initiative for Grid Applications (GIGA)

    Turner, George [MIT Lincoln Lab., Lexington, MA (United States)


    For nearly 4 ½ years, MIT Lincoln Laboratory (MIT/LL) led a very successful, DoE-funded team effort to develop GaN-on-Si materials and devices, targeting high-voltage (>1 kV), high-power, cost-effective electronics for grid applications. This effort, called the GaN Initiative for Grid Applications (GIGA) program, was initially made up of MIT/LL, the MIT campus group of Prof. Tomas Palacios (MIT), and the industrial partner M/A Com Technology Solutions (MTS). Later in the program a 4th team member was added (IQE MA) to provide commercial-scale GaN-on-Si epitaxial materials. A basic premise of the GIGA program was that power electronics, for ubiquitous utilization -even for grid applications - should be closer in cost structure to more conventional Si-based power electronics. For a number of reasons, more established GaN-on-SiC or even SiC-based power electronics are not likely to reach theses cost structures, even in higher manufacturing volumes. An additional premise of the GIGA program was that the technical focus would be on materials and devices suitable for operating at voltages > 1 kV, even though there is also significant commercial interest in developing lower voltage (< 1 kV), cost effective GaN-on-Si devices for higher volume applications, like consumer products. Remarkable technical progress was made during the course of this program. Advances in materials included the growth of high-quality, crack-free epitaxial GaN layers on large-diameter Si substrates with thicknesses up to ~5 μm, overcoming significant challenges in lattice mismatch and thermal expansion differences between Si and GaN in the actual epitaxial growth process. Such thick epilayers are crucial for high voltage operation of lateral geometry devices such as Schottky barrier (SB) diodes and high electron mobility transistors (HEMTs). New “Normally-Off” device architectures were demonstrated – for safe operation of power electronics circuits. The trade-offs between lateral and

  17. GaN Microwave DC-DC Converters

    Ramos Franco, Ignacio

    Increasing the operating frequency of switching converters can have a direct impact in the miniaturization and integration of power converters. The size of energy-storage passive components and the difficulty to integrate them with the rest of the circuitry is a major challenge in the development of a fully integrated power supply on a chip. The work presented in this thesis attempts to address some of the difficulties encountered in the design of high-frequency converters by applying concepts and techniques usually used in the design of high-efficiency power amplifiers and high-efficiency rectifiers at microwave frequencies. The main focus is in the analysis, design, and characterization of dc-dc converters operating at microwave frequencies in the low gigahertz range. The concept of PA-rectifier duality, where a high-efficiency power amplifier operates as a high-efficiency rectifier is investigated through non-linear simulations and experimentally validated. Additionally, the concept of a self-synchronous rectifier, where a transistor rectifier operates synchronously without the need of a RF source or driver is demonstrated. A theoretical analysis of a class-E self-synchronous rectifier is presented and validated through non-linear simulations and experiments. Two GaN class-E2 dc-dc converters operating at a switching frequency of 1 and 1.2 GHz are demonstrated. The converters achieve 80 % and 75 % dc-dc efficiency respectively and are among the highest-frequency and highest-efficiency reported in the literature. The application of the concepts established in the analysis of a self-synchronous rectifier to a power amplifier culminated in the development of an oscillating, self-synchronous class-E 2 dc-dc converter. Finally, a proof-of-concept fully integrated GaN MMIC class-E 2 dc-dc converter switching at 4.6 GHz is demonstrated for the first time to the best of our knowledge. The 3.8 mm x 2.6 mm chip contains distributed inductors and does not require any

  18. Nanostructural engineering of nitride nucleation layers for GaN substrate dislocation reduction.

    Koleske, Daniel David; Lee, Stephen Roger; Lemp, Thomas Kerr; Coltrin, Michael Elliott; Cross, Karen Charlene; Thaler, Gerald


    With no lattice matched substrate available, sapphire continues as the substrate of choice for GaN growth, because of its reasonable cost and the extensive prior experience using it as a substrate for GaN. Surprisingly, the high dislocation density does not appear to limit UV and blue LED light intensity. However, dislocations may limit green LED light intensity and LED lifetime, especially as LEDs are pushed to higher current density for high end solid state lighting sources. To improve the performance for these higher current density LEDs, simple growth-enabled reductions in dislocation density would be highly prized. GaN nucleation layers (NLs) are not commonly thought of as an application of nano-structural engineering; yet, these layers evolve during the growth process to produce self-assembled, nanometer-scale structures. Continued growth on these nuclei ultimately leads to a fully coalesced film, and we show in this research program that their initial density is correlated to the GaN dislocation density. In this 18 month program, we developed MOCVD growth methods to reduce GaN dislocation densities on sapphire from 5 x 10{sup 8} cm{sup -2} using our standard delay recovery growth technique to 1 x 10{sup 8} cm{sup -2} using an ultra-low nucleation density technique. For this research, we firmly established a correlation between the GaN nucleation thickness, the resulting nucleation density after annealing, and dislocation density of full GaN films grown on these nucleation layers. We developed methods to reduce the nuclei density while still maintaining the ability to fully coalesce the GaN films. Ways were sought to improve the GaN nuclei orientation by improving the sapphire surface smoothness by annealing prior to the NL growth. Methods to eliminate the formation of additional nuclei once the majority of GaN nuclei were developed using a silicon nitride treatment prior to the deposition of the nucleation layer. Nucleation layer thickness was determined

  19. Nanostructural engineering of nitride nucleation layers for GaN substrate dislocation reduction.

    Koleske, Daniel David; Lee, Stephen Roger; Lemp, Thomas Kerr; Coltrin, Michael Elliott; Cross, Karen Charlene; Thaler, Gerald


    With no lattice matched substrate available, sapphire continues as the substrate of choice for GaN growth, because of its reasonable cost and the extensive prior experience using it as a substrate for GaN. Surprisingly, the high dislocation density does not appear to limit UV and blue LED light intensity. However, dislocations may limit green LED light intensity and LED lifetime, especially as LEDs are pushed to higher current density for high end solid state lighting sources. To improve the performance for these higher current density LEDs, simple growth-enabled reductions in dislocation density would be highly prized. GaN nucleation layers (NLs) are not commonly thought of as an application of nano-structural engineering; yet, these layers evolve during the growth process to produce self-assembled, nanometer-scale structures. Continued growth on these nuclei ultimately leads to a fully coalesced film, and we show in this research program that their initial density is correlated to the GaN dislocation density. In this 18 month program, we developed MOCVD growth methods to reduce GaN dislocation densities on sapphire from 5 x 10{sup 8} cm{sup -2} using our standard delay recovery growth technique to 1 x 10{sup 8} cm{sup -2} using an ultra-low nucleation density technique. For this research, we firmly established a correlation between the GaN nucleation thickness, the resulting nucleation density after annealing, and dislocation density of full GaN films grown on these nucleation layers. We developed methods to reduce the nuclei density while still maintaining the ability to fully coalesce the GaN films. Ways were sought to improve the GaN nuclei orientation by improving the sapphire surface smoothness by annealing prior to the NL growth. Methods to eliminate the formation of additional nuclei once the majority of GaN nuclei were developed using a silicon nitride treatment prior to the deposition of the nucleation layer. Nucleation layer thickness was determined

  20. Strain engineering of atomic and electronic structures of few-monolayer-thick GaN

    Kolobov, A. V.; Fons, P.; Saito, Y.; Tominaga, J.; Hyot, B.; André, B.


    Two-dimensional (2D) semiconductors possess the potential to ultimately minimize the size of devices and concomitantly drastically reduce the corresponding energy consumption. In addition, materials in their atomic-scale limit often possess properties different from their bulk counterparts paving the way to conceptually novel devices. While graphene and 2D transition-metal dichalcogenides remain the most studied materials, significant interest also exists in the fabrication of atomically thin structures from traditionally 3D semiconductors such as GaN. While in the monolayer limit GaN possesses a graphenelike structure and an indirect band gap, it was recently demonstrated that few-layer GaN acquires a Haeckelite structure in the direction of growth with an effectively direct gap. In this work, we demonstrate the possibility of strain engineering of the atomic and electronic structure of few-monolayer-thick GaN structures, which opens new avenues for their practical application in flexible nanoelectronics and nano-optoelectronics. Our simulations further suggest that due to the weak van der Waals-like interaction between a substrate and an overlayer, the use of a MoS2 substrate may be a promising route to fabricate few-monolayer Haeckelite GaN experimentally.

  1. Morphological characterization of selectively overgrown GaN via lateral epitaxy


    @@ Introduction GaN has attracted a lot of research attention because it has lower Ohmic contact resistance, large electron saturation velocity and a large breakdown field, combined with excellent thermal conductivity and stability, making it an excellent material for high-temperature, high-power and high-brightness optoelectronic devices such as field effect transistors (FET), junction (FET), bipolar transistors and photodiodes[1]. Since threading dislocations resulting from large lattice mismatach and the difference between thermal expansion coefficients of epitaxial GaN and substrate severely degrade the optical and electric qualities of the GaN layer, high quality GaN is indeed required for manufacture of high performance optical device[2]. Characterization of the microstructures of selectively lateral overgrowth of epitaxial GaN using SEM is presented in this work with focus on fully understanding evolution of the morphology and dislocation distribution that occurs in the different growth situations in order for establishment of procession-microstructure-properties interrelations.

  2. The study of electronic structures and optical properties of Al-doped GaN

    Li Enling; Hou Liping; Liu Mancang; Xi Meng; Wang Xiqiang; Dai Yuanbin [Sciences School, Xi' an University of Technology, Xi' an, China 710054 (China); Li Lisha, E-mail:, E-mail: [Physics, Northwest University, Xi' an, China 710068 (China)


    The electronic structures and optical properties of undoped and Al-doped GaN (Al{sub x}Ga{sub 1-x}N, x=0.0625, 0.125, 0.25) have been studied based on generalized gradient approximation (GGA) method of density functional theory (DFT). The differences of the electronic structures and optical properties of undoped and Al-doped GaN have been discussed in detail. The result shows: according to total density of state of undoped and Al-doped GaN, the conduction band becomes width and moves to high energy level with gradual increase concentration of Al impurity. Impurity energy band isn't found in energy band structures of Al{sub x}Ga{sub 1-x}N, the same as energy band structures of undoped GaN, but the band gaps gradually become wide with increase of Al impurity. Absorption spectra of undoped and Al-doped GaN of main absorption peak moves to high energy level with increase of Al impurity.

  3. Effects of catalyst concentration and ultraviolet intensity on chemical mechanical polishing of GaN

    Wang, Jie; Wang, Tongqing; Pan, Guoshun; Lu, Xinchun


    Effects of catalyst concentration and ultraviolet intensity on chemical mechanical polishing (CMP) of GaN were deeply investigated in this paper. Working as an ideal homogeneous substrate material in LED industry, GaN ought to be equipped with a smooth and flat surface. Taking the strong chemical stability of GaN into account, photocatalytic oxidation technology was adopted in GaN CMP process to realize efficient removal. It was found that, because of the improved reaction rate of photocatalytic oxidation, GaN material removal rate (MRR) increases by a certain extent with catalyst concentration increasing. Cross single line analysis on the surface after polishing by Phase Shift MicroXAM-3D was carried out to prove the better removal effect with higher catalyst concentration. Ultraviolet intensity field in H2O2-SiO2-based polishing system was established and simulated, revealing the variation trend of ultraviolet intensity around the outlet of the slurry. It could be concluded that, owing to the higher planarization efficiency and lower energy damage, the UV lamp of 125 W is the most appropriate lamp in this system. Based on the analysis, defects removal model of this work was proposed to describe the effects of higher catalyst concentration and higher power of UV lamp.

  4. The finding of natural GaN crystals in sediments from the East Pacific Ocean

    CHEN Jing; SHI Xuefa; ZHANG Haiping; Lü Huahua; FU Zhendong


    The first finding of natural GaN crystals is reported in sediments from the East Pacific. They are identified by multiple micro-beam techniques such as TEM, EDS and EELS. Detailed examinations show that these GaN crystals are euhedral and authigenic, and belong to the hexagonal system (space group P63mc) with cell parameters: a = b = 0.3186 nm, c = 0.5178 nm. Structure data fit closely with those of the synthetic GaN crystals obtained from high-temperature and high-pressure experiments. Moreover, the nearly perfect euhedral form of the sample excludes the possible synthetic origin of the GaN crystals as artifacts with long transport. The sampling localities are located between the Clarion and Clipperton Fracture Zone in the East Pacific where ongoing hydrothermal activities, deformation, and volcanic eruptions are very intensive. It is suggested that the natural GaN crystals may form at relatively high-temperature and high-pressure conditions in geologic environments that have been affected by intense hydrothermal activities.

  5. The optimal thickness of a transmission-mode GaN photocathode

    Wang Xiao-Hui; Shi Feng; Guo Hui; Hu Cang-Lu; Cheng Hong-Chang; Chang Ben-Kang; Ren Ling; Du Yu-Jie; Zhang Jun-Ju


    A 150-nm-thick GaN photocathode with a Mg doping concentration of 1.6 × 1017 cm-3 is activated by Cs/O in an ultrahigh vacuum chamber,and a quantum efficiency (QE) curve of the negative electron affinity transmission-mode (t-mode) of the GaN photocathode is obtained.The maximum QE reaches 13.0% at 290 nm.According to the t-mode QE equation solved from the diffusion equation,the QE curve is fitted.From the fitting results,the electron escape probability is 0.32,the back-interface recombination velocity is 5 × 104 cm·s-1,and the electron diffusion length is 116 nm.Based on these parameters,the influence of GaN thickness on t-mode QE is simulated.The simulation shows that the optimal thickness of GaN is 90 nm,which is better than the 150-nm GaN.

  6. Nanotexturing of GaN light-emitting diode material through mask-less dry etching

    Dylewicz, Rafal; Khokhar, Ali Z; Rahman, Faiz [School of Engineering, University of Glasgow, Rankine Building, Oakfield Avenue, Glasgow G12 8LT (United Kingdom); Wasielewski, Radoslaw; Mazur, Piotr, E-mail: [Institute of Experimental Physics, University of Wroclaw, plac Maxa Borna 9, 50-204 Wroclaw (Poland)


    We describe a new technique for random surface texturing of a gallium nitride (GaN) light-emitting diode wafer through a mask-less dry etch process. This involves depositing a sub-monolayer film of silica nanospheres (typical diameter of 200 nm) and then subjecting the coated wafer to a dry etch process with enhanced physical bombardment. The silica spheres acting as nanotargets get sputtered and silica fragments are randomly deposited on the GaN epi-layer. Subsequently, the reactive component of the dry etch plasma etches through the exposed GaN surface. Silica fragments act as nanoparticles, locally masking the underlying GaN. The etch rate is much reduced at these sites and consequently a rough topography develops. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) inspections show that random topographic features at the scale of a few tens of nanometres are formed. Optical measurements using angle-resolved photoluminescence show that GaN light-emitting diode material thus roughened has the capability to extract more light from within the epilayers.

  7. Nanotexturing of GaN light-emitting diode material through mask-less dry etching

    Dylewicz, Rafal; Khokhar, Ali Z.; Wasielewski, Radoslaw; Mazur, Piotr; Rahman, Faiz


    We describe a new technique for random surface texturing of a gallium nitride (GaN) light-emitting diode wafer through a mask-less dry etch process. This involves depositing a sub-monolayer film of silica nanospheres (typical diameter of 200 nm) and then subjecting the coated wafer to a dry etch process with enhanced physical bombardment. The silica spheres acting as nanotargets get sputtered and silica fragments are randomly deposited on the GaN epi-layer. Subsequently, the reactive component of the dry etch plasma etches through the exposed GaN surface. Silica fragments act as nanoparticles, locally masking the underlying GaN. The etch rate is much reduced at these sites and consequently a rough topography develops. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) inspections show that random topographic features at the scale of a few tens of nanometres are formed. Optical measurements using angle-resolved photoluminescence show that GaN light-emitting diode material thus roughened has the capability to extract more light from within the epilayers.

  8. Design and Analysis of a 34 dBm Ka-Band GaN High Power Amplifier MMIC

    Heijningen, M. van; Vliet, F.E. van; Quay, R.; Raay, F. van; Seelmann-Eggebert, M.


    This paper presents the design and analysis issues related to the use of recent GaN technologies for realizing high power millimeter wave MMICs. Two GaN Ka-band amplifier MMICs have been designed, fabricated and characterized. The small-signal and power measurement results are presented for both amp

  9. Improved crystalline quality of N-polar GaN epitaxial layers grown with reformed flow-rate-modulation technology

    Zhang, Heng; Zhang, Xiong; Wang, Shuchang; Wang, Xiaolei; Zhao, Jianguo; Wu, Zili; Dai, Qian; Yang, Hongquan; Cui, Yiping


    A reformed flow-rate-modulation technology was developed for the metalorganic vapor phase epitaxy (MOVPE) growth of the N-polar GaN epitaxial layers. To improve the crystalline quality of the N-polar GaN epitaxial layers, a GaN nucleation layer was grown at relatively low temperature with carefully-controlled pulsed supply of Ga source and showed diverse morphology with atomic force microscope (AFM). Furthermore, the electrical and optical properties of the grown N-polar GaN epitaxial layers were investigated extensively by means of Hall effect, photoluminescence (PL), and X-ray rocking curve (XRC) measurements. The characterization results revealed that as compared with the N-polar GaN epitaxial layer grown over the conventional GaN nucleation layer which was deposited with continuous supply of both N and Ga sources, the electrical and optical properties of the N-polar GaN epitaxial layer grown with optimized supply of Ga source for the GaN nucleation layer were significantly improved.

  10. Ultra-Low Inductance Design for a GaN HEMT Based 3L-ANPC Inverter

    Gurpinar, Emre; Castellazzi, Alberto; Iannuzzo, Francesco;


    In this paper, an ultra-low inductance power cell design for a 3L-ANPC based on 650 V GaN HEMT devices is presented. The 3L-ANPC topology with GaN HEMT devices and the selected modulation scheme suitable for wide-bandgap (WBG) devices are presented. The commutation loops, which are the main contr...

  11. Selective etching and TEM study of inversion domains in Mg-doped GaN epitaxial layers

    Kamler, G.; Borysiuk, J.; Weyher, J.L.; Czernecki, R.; Leszczynski, M.; Grzegory, I.; Porowski, S.


    Two different etching techniques were used for the investigation of polarity inversion in the magnesium-doped MOVPE GaN layers deposited on GaN pressure grown substrates. Etching in KOH solution at 100 degrees C and in molten bases at 450 degrees C allowed us to determine precisely the regions of di

  12. A Day For Love


    Young couples drive Valentine’s Day booms in China It is not clear when Chinese couplesstarted celebrating Valentine’s Day,but it has now firmly established itself as an important day around the Spring Festival,

  13. High pressure annealing of Europium implanted GaN

    Lorenz, K.


    GaN epilayers were implanted with Eu to fluences of 1×10^13 Eu/cm2 and 1×10^15 Eu/cm2. Post-implant thermal annealing was performed in ultra-high nitrogen pressures at temperatures up to 1450 ºC. For the lower fluence effective structural recovery of the crystal was observed for annealing at 1000 ºC while optical activation could be further improved at higher annealing temperatures. The higher fluence samples also reveal good optical activation; however, some residual implantation damage remains even for annealing at 1450 ºC which leads to a reduced incorporation of Eu on substitutional sites, a broadening of the Eu luminescence lines and to a strongly reduced fraction of optically active Eu ions. Possibilities for further optimization of implantation and annealing conditions are discussed.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

  14. Optical Properties of GaN and ZnO

    Song, J.-H.

    A brief review on the optical properties of wurtzite ZnO and GaN is presented in this chapter with an emphasis on comparison between the materials. The properties of free excitons and impurity-bound excitons, such as their energetic positions and binding energies, are summarized. The localization energy and the ionization energy of the dominant impurities obtained by emission spectroscopy are also presented. Typical aspects of emissions from donor—acceptor pairs, free-to-bound transition, and deep level recombination are discussed. Several experimental characteristics of the relevant heterostructures, InGaN/GaN and MgZnO/ZnO, are also given below. Basic optical methods characterizing the effects of internal electric fields and carrier-localization are summarized. The unique properties of polarization sensitive emissions from nonpolar films are presented. Based on the valence band structures, the polarization selection rules can be obtained in simpler forms. Some recent reports will also be introduced stating that the anisotropic strain in nonpolar films plays an important role in deciding the polarization selectivity. The results of Raman spectroscopy are summarized in the end, with the emphasis on deciding the residual strain and the carrier concentration.

  15. Photoluminescence of localized excitons in InGan quantum dots

    Usov, S. O., E-mail:; Tsatsul' nikov, A. F.; Lundin, V. V.; Sakharov, A. V.; Zavarin, E. E.; Ledentsov, N. N. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)


    Photoluminescence spectra of samples with ultrathin InGaN layers embedded in AlGaN and GaN matrices are studied experimentally in the temperature range of 80 to 300 K. It is shown that the temperature dependences can be understood in the context of Eliseev's model and that, in the active region of the structures under study, the dispersion {sigma} of the exciton-localization energy depends on the average In content in InGaN-alloy layers. Furthermore, the Urbach energy E{sub U}, which characterizes the localization energy of excitons in the tails of the density of states, was determined from an analysis of the shape of the low-energy slope of the spectrum. It is shown that {sigma} and E{sub U}, quantities representing the scale of the exciton-localization effects, vary linearly with the photoluminescence-peak wavelength in the range from the ultraviolet to the green region of the spectrum.

  16. AMIE Gan Island Ancillary Disdrometer Field Campaign Report

    Oue, Mariko [Stony Brook Univ., NY (United States)


    As part of the U.S. Department of Energy (DOE)’s Atmospheric Radiation Measurement Climate Research Facility (ARM) Madden-Julian Oscillation (MJO) Investigation Experiment (AMIE), in January 2012 a disdrometer observation took place with the second ARM Mobile Facility (AMF2), the Scanning ARM Cloud Radar (SACR), the Texas A&M SMART-R C-band radar, and the National Center for Atmospheric Research (NCAR) dual wavelength S- and Ka-bands polarimetric (SPolKa) radar on Gan Island, Maldives. In order to measure raindrop size distributions, a disdrometer of Nagoya University, Japan, was set up close to the ARM Two-Dimensional (2D) Video Disdrometer (2DVD). The SMART-R and SPolKa radars performed range-height-indicator scanning in the direction of the disdrometer site. Comparing the disdrometer data with 2DVD data, the raindrop size distribution data will be calibrated. Furthermore, the analysis of the raindrop size distribution and radar data will be expected to clarify the microphysics in tropical convective clouds.

  17. High pressure luminescence studies of europium doped GaN

    K.Wisniewski; W.Jadwisie(n)czak; T.Thomas; M.Spencer


    We reported on the high pressure luminescence spectra of polycrystalline Eu-doped GaN material synthesized in the reaction tween alloys of gallium,bismuth and europium in ammonia atmosphere.The integrated luminescence intensity of the dominant Eu3+ ion transition (5D0→7F2) at 622 nm increased approximately one order of magnitude whereas its spectral position and line width did not change significantly between ambient and 6.8 GPa pressure,respectively.Moreover,material was characterized with photo- and cathodo-luminescence,and photoluminescence excitation spectra at different temperatures.It was found that the Eu3+ ions occupying substitutional Ga site created different centers which could be effectively excited with above band gap excitation and from excitons resonantly photoexcited at the I2 bound exciton energy.Furthermore,the less efficient Eu3+ ions excitation path existed through intrinsic impurities and defects generating shallow energy levels in the forbidden gap.It was proposed that reduction of the thermal quenching and consequent enhancement of Eu3+ ion emission intensity resulted from stronger localization of bound exciton on RESI trap induced by applied pressure.

  18. Simulations of electron transport in GaN devices

    Arabshahi, H


    model of a device with traps to investigate this suggestion. The model includes the simulation of the capture and release of electrons by traps whose charge has a direct effect on the current flowing through the transistor terminals. The influence of temperature and light on the occupancy of the traps and the I-V characteristics are considered. It is concluded that traps are likely to play a substantial role in the behaviour of GaN field effect transistors. Further simulations were performed to model electron transport in AIGaN/GaN heterojunction FETs. So called HFET structures with a 78 nm Al sub 0 sub . sub 2 Ga sub 0 sub . sub 8 N pseudomorphically strained layer have been simulated, with the inclusion of spontaneous and piezoelectric polarization effects in the strained layer. The polarization effects are shown to not only increase the current density, but also improve the electron transport by inducing a higher electron density close to the positive charge sheet that occurs in the channel. This thesis de...

  19. Synthesis of GaN nanorods on Si substrates with assistance of the volatilization of ZnO middle layers

    ZHUANG Huizhao; GAO Haiyong; XUE Chengshan; WANG Shuyun; DONG Zhihua; HE Jianting


    GaN nanorods have successfully been synthesized on Si(111) substrates via ammoniating ZnO/Ga2O3 films at 950℃. Ga2O3 thin films and ZnO middle layers were deposited in turn on Si(111) substrates by r.f. magnetron sputtering system. ZnO volatilized at 950℃ in the ammonia ambience and Ga2O3 reacted to NH3 to fabricate GaN nanorods in the later ammoniating process. The volatilization of ZnO layers played an important role in the fabrication. The structure and composition of the GaN nanorods were studied by X-ray diffraction (XRD) and Fourier transform infrared spectrophotometer (FTIR). The morphology of GaN nanorods was investigated using scanning electron microscopy (SEM) and transmission electronic microscope (TEM). The analyses of measured results revealed that GaN nanorods with hexagonal wurtzite structure were prepared by this method.

  20. Growth and Characterization of N-Polar GaN Films on Si(111) by Plasma Assisted Molecular Beam Epitaxy

    Dasgupta, Sansaptak; Nidhi; Wu, Feng; Speck, James S.; Mishra, Umesh K.


    Smooth N-polar GaN films were epitaxially grown by plasma assisted molecular beam epitaxy (PAMBE) on on-axis p-Si(111). The structural quality of the as-grown GaN films was further improved by insertion of AlGaN/GaN superlattice structures, resulting in reduced threading dislocation density and also efficient stress management in the GaN film to mitigate crack formation. The structural quality of these films was comparable to N-polar GaN grown on C-SiC by MBE. Convergent beam electron diffraction (CBED) imaging and KOH etch studies were performed to confirm the N-polarity of the sample. Room temperature photoluminescence measurements revealed strong GaN band-edge emission.

  1. Preparation of Freestanding GaN Wafers by Hydride Vapor Phase Epitaxy with Void-Assisted Separation

    Oshima, Yuichi; Eri, Takeshi; Shibata, Masatomo; Sunakawa, Haruo; Kobayashi, Kenji; Ichihashi, Toshinari; Usui, Akira


    We have developed a novel technique for preparing large-scale freestanding GaN wafers. Hydride vapor phase epitaxy (HVPE) growth of thick GaN layer was performed on a GaN template with a thin TiN film on the top. After the cooling process of the HVPE growth, the thick GaN layer was easily separated from the template by the assistance of many voids generated around the TiN film. As a result, a freestanding GaN wafer was obtained. The wafer obtained had a diameter of 45 mm, and a mirror-like surface. The-full-width-at-half-maximum (FWHM) of (0002) and (10\\bar{1}0) peaks in the X-ray rocking curve profile were 60 and 92 arcsec, respectively. The dislocation density was evaluated at 5× 106 cm-3 by etch pit density measurement.

  2. Correlation of doping, structure, and carrier dynamics in a single GaN nanorod

    Zhou, Xiang; Lu, Ming-Yen; Lu, Yu-Jung; Gwo, Shangjr; Gradečak, Silvija


    We report the nanoscale optical investigation of a single GaN p-n junction nanorod by cathodoluminescence (CL) in a scanning transmission electron microscope. CL emission characteristic of dopant-related transitions was correlated to doping and structural defect in the nanorod, and used to determine p-n junction position and minority carrier diffusion lengths of 650 nm and 165 nm for electrons and holes, respectively. Temperature-dependent CL study reveals an activation energy of 19 meV for non-radiative recombination in Mg-doped GaN nanorods. These results directly correlate doping, structure, carrier dynamics, and optical properties of GaN nanostructure, and provide insights for device design and fabrication.

  3. On the phenomenon of large photoluminescence red shift in GaN nanoparticles

    Ben Slimane, Ahmed


    We report on the observation of broad photoluminescence wavelength tunability from n-type gallium nitride nanoparticles (GaN NPs) fabricated using the ultraviolet metal-assisted electroless etching method. Transmission and scanning electron microscopy measurements performed on the nanoparticles revealed large size dispersion ranging from 10 to 100 nm. Nanoparticles with broad tunable emission wavelength from 362 to 440 nm have been achieved by exciting the samples using the excitation power-dependent method. We attribute this large wavelength tunability to the localized potential fluctuations present within the GaN matrix and to vacancy-related surface states. Our results show that GaN NPs fabricated using this technique are promising for tunable-color-temperature white light-emitting diode applications. © 2013 Slimane et al.; licensee Springer.

  4. Effects of Dislocation on High Temperature Transport Characteristics of Unintentionally Doped GaN

    WANG Mao-Jun; SHEN Bo; XU Fu-Jun; WANG Yan; XU Jian; HUANG Sen; YANG Zhi-Jian; QIN Zhi-Xin; ZHANG Guo-Yi


    High temperature transport characteristics of unintentionally doped GaN have been investigated by means of high temperature Hall measurements from room temperature to 50CPC. The increment of electron concentration from room temperature to 500°C is found to vary largely for different samples. The dispersion of temperature dependence of electron concentration is found to be directly proportional to the density of dislocations in GaN layers calculated by fitting the FWHM of the rocking curves in x-ray diffraction measurements (XRD). The buildup levels in persistent photoconductivity (PPC) are also shown to be directly proportional to the density of dislocations. The correlation of XRD, Hall and PPC results indicate that the high temperature dependence of electron density in unintentional doped GaN is directly dislocation related.

  5. Measurement of the electrostatic edge effect in wurtzite GaN nanowires

    Henning, Alex; Rosenwaks, Yossi [Department of Physical Electronics, School of Electrical Engineering, Tel-Aviv University, Ramat-Aviv 69978 (Israel); Klein, Benjamin [School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States); Bertness, Kris A.; Blanchard, Paul T.; Sanford, Norman A. [NIST, Physical Measurement Laboratory, Division 686, 325 Broadway, Boulder, Colorado 80305 (United States)


    The electrostatic effect of the hexagonal corner on the electronic structure in wurtzite GaN nanowires (NWs) was directly measured using Kelvin probe force microscopy (KPFM). By correlating electrostatic simulations with the measured potential difference between the nanowire face and the hexagonal vertices, the surface state concentration and band bending of GaN NWs were estimated. The surface band bending is important for an efficient design of high electron mobility transistors and for opto-electronic devices based on GaN NWs. This methodology provides a way to extract NW parameters without making assumptions concerning the electron affinity. We are taking advantage of electrostatic modeling and the high precision that KPFM offers to circumvent a major source of uncertainty in determining the surface band bending.

  6. Formation of aligned CrN nanoclusters in Cr-delta-doped GaN

    Zhou, Y K; Kimura, S; Emura, S; Hasegawa, S; Asahi, H [Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)], E-mail:


    Cr-delta-doped GaN layers were grown by radio-frequency plasma-assisted molecular-beam epitaxy on GaN template substrates. Cr flux was supplied without nitrogen flow during Cr-delta-doping. Cr incorporation into a narrow thin layer region was confirmed with the depth profile measured by secondary ion mass spectrometry. Structural properties and Cr atom alignments were studied with transmission electron microscopy. It was found that Cr-delta-doped GaN layers were coherently grown with Cr or CrGa nanoclusters in the delta-doped region for low temperature growth (350, 500 deg. C). It was also found that aligned CrN nanoclusters (approximately 5 nm vertical thickness) with NaCl-type structure were formed in the delta-doped region for the growth at 700 deg. C.


    Dhiyauddin Ahmad Fauzi


    Full Text Available In addition to their useful optoelectronics functions, gallium nitride (GaN and quantum dots (QDs based structures are also known for their radiation hardness properties. With demands on such semiconductor material structures, it is important to investigate the differences in reliability and radiation hardness properties of these two devices. For this purpose, three sets of GaN light-emitting diode (LED and InAs/GaAs dot-in-a well (DWELL samples were irradiated with thermal neutron of fluence ranging from 3×1013 to 6×1014 neutron/cm2 in PUSPATI TRIGA research reactor. The radiation performances for each device were evaluated based on the current-voltage (I-V and capacitance-voltage (C-V electrical characterisation method. Results suggested that the GaN based sample is less susceptible to electrical changes due to the thermal neutron radiation effects compared to the QD based sample.

  8. Study of electrical properties of single GaN nanowires grown by molecular beam epitaxy

    Mozharov, A. M.; Komissarenko, F. E.; Vasiliev, A. A.; Bolshakov, A. D.; Moiseev, E. I.; Mukhin, M. S.; Cirlin, G. E.; Mukhin, I. S.


    Electrical properties of single GaN nanowires grown by means of molecular beam epitaxy with N-plasma source were studied. Ohmic contacts connected to single n-type GaN wires were produced by the combination of electron beam lithography, metal vacuum evaporation and rapid thermal annealing technique. The optimal annealing temperature to produce ohmic contacts implemented in the form of Ti/Al/Ti/Au stack has been determined. By means of 2-terminal measurement wiring diagram the conductivity of single NW has been obtained for NWs with different growth parameters. The method of MESFET measurement circuit layout of single GaN nanowires (NWs) has been developed. In accordance with performed numerical calculation, free carriers' concentration and mobility of single NWs could be independently estimated using MESFET structure.

  9. Ammonothermal synthesis of GaN using Ba(NH2)2 as mineralizer

    Hertrampf, J.; Alt, N. S. A.; Schlücker, E.; Knetzger, M.; Meissner, E.; Niewa, R.


    It is demonstrated that hexagonal GaN can be obtained under ammonothermal conditions (125 MPa and 723 K) using Ba(NH2)2 as mineralizer. The hexagonal wurtzite-type GaN crystallites are several μm in diameter, as examined by scanning electron microscopy. This is to our knowledge the first successful ammonothermal GaN synthesis using an alkaline-earth metal as mineralizer. Ba[Ga(NH2)4]2 was identified as intermediate species in the ammonothermal synthesis process. The formation of h-GaN using Sr(NH2)2 as mineralizer was indicated only at higher temperatures above 1000 K.

  10. Semipolar AlN and GaN on Si(100): HVPE technology and layer properties

    Bessolov, V.; Kalmykov, A.; Konenkova, E.; Kukushkin, S.; Myasoedov, A.; Poletaev, N.; Rodin, S.


    Hydride vapor phase epitaxy (HVPE) growth of semipolar AlN and GaN layers on planar Si(100) substrates with SiC nanolayer is investigated. It is shown experimentally that the solid-phase epitaxial formation of a specially oriented SiC nucleation layer followed by epitaxy of AlN layer by HVPE at low rates enables growth of aluminum and gallium nitrides in the semipolar direction. For the best GaN(20-23) layers obtained, the full width at half maximum (FWHM) value for the x-ray diffraction rocking curve is 24 arcmin. The photoluminescence spectrum of the semipolar GaN measured at 4 K exhibits bands related to basal-plane and prismatic stacking faults (BSF and PSF).

  11. The pyroelectric coefficient of free standing GaN grown by HVPE

    Jachalke, Sven; Hofmann, Patrick; Leibiger, Gunnar; Habel, Frank S.; Mehner, Erik; Leisegang, Tilmann; Meyer, Dirk C.; Mikolajick, Thomas


    The present study reports on the temperature dependent pyroelectric coefficient of free-standing and strain-free gallium nitride (GaN) grown by hydride vapor phase epitaxy (HVPE). The Sharp-Garn method is applied to extract the pyroelectric coefficient from the electrical current response of the crystals subjected to a sinusoidal temperature excitation in a range of 0 °C to 160 °C. To avoid compensation of the pyroelectric response by an internal conductivity, insulating GaN crystals were used by applying C, Mn, and Fe doping during HVPE growth. The different pyroelectric coefficients observed at room temperature due to the doping correlate well with the change of the lattice parameter c. The obtained data are compared to previously published theoretical and experimental values of thin film GaN and discussed in terms of a strained lattice.

  12. A high efficiency C-band internally-matched harmonic tuning GaN power amplifier

    Lu, Y.; Zhao, B. C.; Zheng, J. X.; Zhang, H. S.; Zheng, X. F.; Ma, X. H.; Hao, Y.; Ma, P. J.


    In this paper, a high efficiency C-band gallium nitride (GaN) internally-matched power amplifier (PA) is presented. This amplifier consists of 2-chips of self-developed GaN high-electron mobility transistors (HEMTs) with 16 mm total gate width on SiC substrate. New harmonic manipulation circuits are induced both in the input and output matching networks for high efficiency matching at fundamental and 2nd-harmonic frequency, respectively. The developed amplifier has achieved 72.1% power added efficiency (PAE) with 107.4 W output power at 5 GHz. To the best of our knowledge, this amplifier exhibits the highest PAE in C-band GaN HEMT amplifiers with over 100 W output power. Additionally, 1000 hours' aging test reveals high reliability for practical applications.

  13. Integrated GaN photonic circuits on silicon (100) for second harmonic generation

    Xiong, Chi; Ryu, Kevin K; Schuck, Carsten; Fong, King Y; Palacios, Tomas; Tang, Hong X


    We demonstrate second order optical nonlinearity in a silicon architecture through heterogeneous integration of single-crystalline gallium nitride (GaN) on silicon (100) substrates. By engineering GaN microrings for dual resonance around 1560 nm and 780 nm, we achieve efficient, tunable second harmonic generation at 780 nm. The \\{chi}(2) nonlinear susceptibility is measured to be as high as 16 plus minus 7 pm/V. Because GaN has a wideband transparency window covering ultraviolet, visible and infrared wavelengths, our platform provides a viable route for the on-chip generation of optical wavelengths in both the far infrared and near-UV through a combination of \\{chi}(2) enabled sum-/difference-frequency processes.

  14. Self-induced growth of vertical GaN nanowires on silica

    Kumaresan, V.; Largeau, L.; Oehler, F.; Zhang, H.; Mauguin, O.; Glas, F.; Gogneau, N.; Tchernycheva, M.; Harmand, J.-C.


    We study the self-induced growth of GaN nanowires on silica. Although the amorphous structure of this substrate offers no possibility of an epitaxial relationship, the nanowires are remarkably aligned with the substrate normal whereas, as expected, their in-plane orientation is random. Their structural and optical characteristics are compared to those of GaN nanowires grown on standard crystalline Si (111) substrates. The polarity inversion domains are much less frequent, if not totally absent, in the nanowires grown on silica, which we find to be N-polar. This work demonstrates that high-quality vertical GaN nanowires can be elaborated without resorting to bulk crystalline substrates.

  15. Investigation of HCl-based surface treatment for GaN devices

    Okada, Hiroshi, E-mail: [Electronics-Inspired Interdisciplinary Research Institute (EIIRIS), Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi 441-8580 (Japan); Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi 441-8580 (Japan); Shinohara, Masatohi; Kondo, Yutaka; Sekiguchi, Hiroto; Yamane, Keisuke [Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi 441-8580 (Japan); Wakahara, Akihiro [Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi 441-8580 (Japan); Electronics-Inspired Interdisciplinary Research Institute (EIIRIS), Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi 441-8580 (Japan)


    Surface treatments of GaN in HCl-based solutions are studied by X-ray photoelectron spectroscopy (XPS) and electrical characterization of fabricated GaN surfaces. A dilute-HCl treatment (HCl:H{sub 2}O=1:1) at room temperature and a boiled-HCl treatment (undiluted HCl) at 108°C are made on high-temperature annealed n-GaN. From the XPS study, removal of surface oxide by the dilute-HCl treatment was found, and more thoroughly oxide-removal was confirmed in the boiled-HCl treatment. Effect of the surface treatment on electrical characteristics on AlGaN/GaN transistor is also studied by applying treatment processes prior to the surface SiN deposition. Increase of drain current is found in boiled-HCl treated samples. The results suggest that the boiled-HCl treatment is effective for GaN device fabrication.

  16. Analysis and modelling of GaN Schottky-based circuits at millimeter wavelengths

    Pardo, D.; Grajal, J.


    This work presents an analysis of the capabilities of GaN Schottky diodes for frequency multipliers and mixers at millimeter wavelengths. By using a Monte Carlo (MC) model of the diode coupled to a harmonic balance technique, the electrical and noise performances of these circuits are investigated. Despite the lower electron mobility of GaN compared to GaAs, multipliers based on GaN Schottky diodes can be competitive in the first stages of multiplier chains, due to the excellent power handling capabilities of this material. The performance of these circuits can be improved by taking advantage of the lateral Schottky diode structures based on AlGaN/GaN HEMT technology.

  17. Nonresonant tunneling phonon depopulated GaN based terahertz quantum cascade structures

    Freeman, Will; Karunasiri, Gamani


    GaN based terahertz quantum cascade structures are theoretically studied. Since the Fröhlich interaction is ˜15 times higher in GaN than in GaAs, level broadening makes obtaining appreciable optical gain difficult even with a large population inversion. A density matrix Monte Carlo method is used to calculate the broadening of the optical gain spectra as a function of lattice temperature. We find by using a proposed method of nonresonant tunneling and electron-longitudinal-optical phonon scattering for depopulation of the lower lasing state, that it is possible to sufficiently isolate the upper lasing state and control the lower lasing state lifetime to obtain high optical gain in GaN. The results predict lasing out to 300 K which is significantly higher than for GaAs based structures.

  18. Visualization of GaN surface potential using terahertz emission enhanced by local defects

    Sakai, Yuji; Kawayama, Iwao; Nakanishi, Hidetoshi; Tonouchi, Masayoshi


    Wide-gap semiconductors have received significant attention for their advantages over existing semiconductors in energy-efficient power devices. To realize stable and reliable wide-gap semiconductor devices, the basic physical properties, such as the electric properties on the surface and at the interface, should be revealed. Here, we report visualization of terahertz (THz) emission from the surface of GaN, which is excited by ultraviolet femtosecond laser pulses. We found that the THz emission is enhanced by defects related to yellow luminescence, and this phenomenon is explained through the modification of band structures in the surface depletion layer owing to trapped electrons at defect sites. Our results demonstrate that the surface potential in a GaN surface could be detected by laser-induced THz emission. Moreover, this method enables feasible evaluation of the distribution of non-radiative defects, which are undetectable with photoluminescence, and it contributes to the realization normally-off GaN devices.

  19. Botulinum toxin detection using AlGaN /GaN high electron mobility transistors

    Wang, Yu-Lin; Chu, B. H.; Chen, K. H.; Chang, C. Y.; Lele, T. P.; Tseng, Y.; Pearton, S. J.; Ramage, J.; Hooten, D.; Dabiran, A.; Chow, P. P.; Ren, F.


    Antibody-functionalized, Au-gated AlGaN /GaN high electron mobility transistors (HEMTs) were used to detect botulinum toxin. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN /GaN HEMT drain-source current showed a rapid response of less than 5s when the target toxin in a buffer was added to the antibody-immobilized surface. We could detect a range of concentrations from 1to10ng/ml. These results clearly demonstrate the promise of field-deployable electronic biological sensors based on AlGaN /GaN HEMTs for botulinum toxin detection.


    J. Xu; R. Zhang; Y.P. Wang; X.Q. Xiu; S.L. Gu; B. Shen; Y. Shi; Z.G. Liu; Y.D. Zheng


    Gallium Nitride film was successfully separated from sapphire substrate by laser radi-ation. The absorption of the 248nm radiation by the GaN at the interface results inrapid thermal decomposition of the interfacial layer, yielding metallic Ga and N2 gas.The substrate can be easily removed by heating above the Ga melting point (29℃).X-ray diffraction, atomic force microscopy and Photoluminescence of GaN before andafter lift-off process have been performed, which demonstrated that the separation andtransfer process do not alter the structural quality of the GaN films. And further dis-cussions on the threshold energy and crack-free strategies of laser lift-off process havealso been presented.

  1. High-pressure X-ray diffraction study of bulk- and nanocrystalline GaN

    Jorgensen, J.E.; Jakobsen, J.M.; Jiang, Jianzhong;


    Bulk- and nanocrystalline GaN have been studied by high-pressure energy-dispersive X-ray diffraction. Pressure-induced structural phase transitions from the wurtzite to the NaCl phase were observed in both materials. The transition pressure was found to be 40 GPa for the bulk-crystalline GaN, while...... the wurtzite phase was retained up to 60 GPa in the case of nanocrystalline GaN. The bulk moduli for the wurtzite phases were determined to be 187 ( 7) and 319 ( 10) GPa for the bulk- and nanocrystalline phases, respectively, while the respective NaCl phases were found to have very similar bulk moduli [ 208...

  2. A low cost, green method to synthesize GaN nanowires

    Zhao, Jun-Wei; Zhang, Yue-Fei; Li, Yong-He; Su, Chao-Hua; Song, Xue-Mei; Yan, Hui; Wang, Ru-Zhi


    The synthesis of gallium nitride nanowires (GaN NWs) by plasma enhanced chemical vapor deposition (PECVD) are successfully demonstrated in this work. The simple and green synthesis route is to introduce gallium oxide (Ga2O3) and nitrogen (N2) for the growth of nanowires. The prepared GaN nanowires have a single crystalline wurtzite structure, which the length of some nanowires is up to 20 μm, with a maximum diameter about 140 nm. The morphology and quantity of the nanowires can be modulated by the growth substrate and process parameters. In addition, the photoluminescence and field emission properties of the prepared GaN nanowires have been investigated, which were found to be largely affected by their structures. This work renders an environmentally benign strategy and a facile approach for controllable structures on nanodevice.

  3. Patterned growth of InGaN/GaN quantum wells on freestanding GaN grating by molecular beam epitaxy

    Wang Yongjin; Hu Fangren; Hane Kazuhiro


    Abstract We report here the epitaxial growth of InGaN/GaN quantum wells on freestanding GaN gratings by molecular beam epitaxy (MBE). Various GaN gratings are defined by electron beam lithography and realized on GaN-on-silicon substrate by fast atom beam etching. Silicon substrate beneath GaN grating region is removed from the backside to form freestanding GaN gratings, and the patterned growth is subsequently performed on the prepared GaN template by MBE. The selective growth takes place wit...

  4. Controlling the morphology of GaN layers grown on AlN in Ga self-surfactant conditions: from quantum wells to quantum dots

    Adelmann, C.; Daudin, B.; Monroy, E.; Sarigiannidou, E.; Rouviere, J.L.; Hori, Y.; Brault, J.; Gogneau, N. [Departement de Recherche Fondamentale sur la Matiere Condensee, SP2M/PSC, CEA-Grenoble, 17 rue des Martyrs, 38054-Grenoble Cedex 9 (France); Fanget, S.; Bru-Chevallier, C. [Laboratoire de Physique de la Matiere - CNRS (UMR5511), INSA de Lyon, Batiment Blaise Pascal, 7 avenue Jean Capelle, 69621 Villeurbanne Cedex (France)


    We show that the growth mode of GaN deposited by plasma-assisted molecular beam epitaxy on AlN can be controlled by tuning Ga/N ratio. This enables to grow either quantum dots (Ga/N<1) or quantum wells (Ga/N>>1). The inhibition of 2D/3D transition results from a decrease in effective mismatch induced by the presence of a continuous Ga film on growing GaN surface in Ga-rich conditions. (Abstract Copyright [2002], Wiley Periodicals, Inc.)

  5. A survey on GaN- based devices for terahertz photonics

    Ahi, Kiarash; Anwar, Mehdi


    With fast growing of the photonics and power electronic systems, the need for high power- high frequency semiconductor devices is sensed tremendously. GaN provides the highest electron saturation velocity, breakdown voltage and operation temperature, and thus combined frequency-power performance among commonly used semiconductors. With achieving the first THz image in just two decades ago, generation and detection of terahertz (THz) radiation is one of the most emerging photonic areas. The industrial needs for compact, economical, high resolution and high power THz imaging and spectroscopy systems are fueling the utilization of GaN for the realizing of the next generation of THz systems. As it is reviewed in this paper, the mentioned characteristics of GaN together with its capabilities of providing high 2-dimentional election densities and large longitudinal-optical phonon of 90 meV, make it one of the most promising semiconductor materials for the future of the THz generation, detection, mixing, and frequency multiplication. GaN- based devices have shown capabilities of operating in the upper THz frequency band of 5- 12 THz with relatively high photon densities and in room temperature. As a result, THz imaging and spectroscopy systems with high resolutions and depths of penetrations can be realized via utilizing GaN- based devices. In this paper, a comprehensive review on the history and state of the art of the GaN- based electronic devices, including plasma HFETs, NDRs, HDSDs, IMPATTs, QCLs, HEMTs, Gunn diodes and TeraFETs together with their impact on the future of THz imaging and spectroscopy systems is provided.

  6. Gosha-jinki-gan (a Herbal Complex Corrects Abnormal Insulin Signaling

    Bolin Qin


    Full Text Available Previous studies have shown that the traditional herbal complex Gosha-jinki-gan (GJG improves diabetic neuropathy and insulin resistance. The present study was undertaken to elucidate the molecular mechanisms related with the long-term effects of GJG administration on insulin action in vivo and the early steps of insulin signaling in skeletal muscle in streptozotocin (STZ diabetes. Rats were randomized into five subgroups: (1 saline treated control, (2 GJG treated control, (3 2-unit insulin + saline treated diabetic, (4 saline + GJG treated diabetic and (5 2-unit insulin + GJG treated diabetic groups. After seven days of treatment, euglycemic clamp experiment at an insulin infusion rate of 6 mU/kg/min was performed in overnight fasted rats. Despite the 2-unit insulin treatment, the metabolic clearance rates of glucose (MCR, ml/kg/min in diabetic rats were significantly lower compared with the controls (11.4 ± 1.0 vs 44.1 ± 1.5; P < 0.001, and were significantly improved by insulin combined with GJG or GJG alone (26 ± 3.2 and 24.6 ± 2.2, P < 0.01, respectively. The increased insulin receptor (IR-β protein content in skeletal muscle of diabetic rats was not affected by insulin combined with GJG administration. However, the decreased insulin receptor substrate-1 (IRS-1 protein content was significantly improved by treatment with GJG. Additionally, the increased tyrosine phosphorylation levels of IR-β and IRS-1 were significantly inhibited in insulin combined with GJG treated diabetes. The present results suggest that the improvement of the impaired insulin sensitivity in STZ-diabetic rats by administration of GJG may be due, at least in part, to correction in the abnormal early steps of insulin signaling in skeletal muscle.

  7. Mother’s Day



    Mother’s Day is a day for each family to honor (尊敬,给……以光荣) its mother ,celebrated (庆祝)on various days in many places around the world.It complements (补足,补充) Father’s Day,the celebration

  8. Structural features in GaN grown on a Ge(111) substrate

    Zhang, Y.; McAleese, C.; Xiu, H.; Humphreys, C.J. [Department of Materials Science and Metallurgy, University of Cambridge (United Kingdom); Lieten, R.R.; Degroote, S.; Borghs, G. [Interuniversity Microelectronics Center, Leuven (Belgium)


    Using electron microscopy, structural characterisation has been carried out on a GaN epilayer grown directly on a Ge(111) substrate using plasma assisted molecular beam epitaxy (PAMBE) without any intermediate buffer layers. It was determined that a defect with a triangular shape, initially observed with optical microscopy, is essentially a faceted void in the Ge extending from the interface into the substrate. Both hexagonal and cubic phase GaN were observed in the epilayer which may be due to temperature variation during growth. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Luminescence of GaN nanocolumns obtained by photon-assisted anodic etching

    Tiginyanu, I. M.; Ursaki, V. V.; Zalamai, V. V.; Langa, S.; Hubbard, S.; Pavlidis, D.; Föll, H.


    GaN nanocolumns with transverse dimensions of about 50 nm were obtained by illumination-assisted anodic etching of epilayers grown by metalorganic chemical vapor deposition on sapphire substrates. The photoluminescence spectroscopy characterization shows that the as-grown bulk GaN layers suffer from compressive biaxial strain of 0.5 GPa. The majority of nanocolumns are fully relaxed from strain, and the room-temperature luminescence is free excitonic. The high quality of the columnar nanostructures evidenced by the enhanced intensity of the exciton luminescence and by the decrease of the yellow luminescence is explained by the peculiarities of the anodic etching processing.

  10. Determination of satellite valley position in GaN emitter from photoexcited field emission investigations

    Semenenko, M.; Yilmazoglu, O.; Hartnagel, H. L.; Pavlidis, D.


    Argon plasma etched GaN field-emitter rods with nanometer-scale diameter were fabricated on GaN grown on an n+-GaN substrate. Their electron field emission properties were investigated both without and under illumination by using light sources with various wavelengths. The Fowler-Nordheim current-voltage characteristics of the cathodes show a change in slope for illuminated cathodes. The electron affinity difference ΔE between the different valleys in the conduction band has been ascertained and is in the range from 1.18 up to 1.21 eV.

  11. Optical anisotropy and light extraction efficiency of MBE grown GaN nanowires epilayers.

    Henneghien, Anne-Line; Tourbot, Gabriel; Daudin, Bruno; Lartigue, Olivier; Désières, Yohan; Gérard, Jean-Michel


    The use of nanowires as active medium seems very promising for the development of high brightness LEDs. With a lower effective refractive index than bulk, semiconductor nanowire layers may lead to a high light extraction efficiency. We hereafter discuss the anisotropic properties of dense arrays of molecular beam epitaxy (MBE) grown gallium nitride (GaN) nanowires and the consequences on the optical design of nanowire based LEDs. In particular we show numerically that light extraction efficiency as high as 72% can be expected for GaN nanowires layer grown on a low cost Si substrate.

  12. Extraction of absorption coefficients from GaN nanowires grown on opaque substrates

    Jayaprakash, Rahul; Germanis, Savvas; Androulidaki, Maria; Tsagaraki, Katerina; Georgakilas, Alexandros; Pelekanos, Nikos T


    We demonstrate a new method to measure absorption coefficients in any family of nanowires, provided they are grown on a substrate having considerable difference in permittivity with the nanowire-air matrix. In the case of high crystal quality, strain-free GaN nanowires, grown on Si (111) substrates with a density of ~1010 cm-2, the extracted absorption coefficients do not exhibit any enhancement compared to bulk GaN values, unlike relevant claims in the literature. This may be attributed to the relatively small diameters, short heights, and high densities of our nanowire arrays.

  13. A forgotten Ottoman composer: Ali Şîrûganî Dede

    M. Emin Soydaş


    Full Text Available Although being one of the major composers of religious music in the Ottoman era, Ali Şîrûganî Dede, who was famous throughout his life as well as afterwards, is not known nowadays much well as he deserves. In this article Ali Şîrûganî Dede is introduced and information is given on his musicianship and his works, while his situation in the history of Ottoman music is pointed out and especially his importance with regard to religious music is emphasized. Some new information about the subject is also presented within this work.

  14. Characterization of an Mg-implanted GaN p-i-n Diode


    The Mg-implanted p-i-n diode exhibits rectification and low leakage currents. The realization of an Mg-implanted GaN device is a key step for...future power electronic devices. Keywords: GaN, p-i-n diode, ion implantation Introduction III-nitride materials have attracted a continuous interest...implantation to a concentration of 2x1019 cm-3 following a box profile to a depth of 500nm. A photoresist mask was used for the implantation, aligned to

  15. GaN ultraviolet detector based demonstrator board for UV-index monitoring

    Song, Man; Xie, Feng; Wang, Jun; Wang, Tanglin; Guo, Jin


    Currently, various types of III nitride-based materials have been successfully used for short-wavelength optoelectronic devices. The GaN ultraviolet detector has been wildly used for UV-Index(UVI) monitoring, UV curing and water disinfection. The global solar UVI describes the levels of solar UV radiation at the Earth's surface. The higher the UVI value, the greater the potential damage to the skin and eyes. The UVI monitoring demonstrator board with GaN detector is briefly introduced in this paper.

  16. Nucleation and Growth of GaN on GaAs (001) Substrates

    Drummond, Timothy J.; Hafich, Michael J.; Heller, Edwin J.; Lee, Stephen R.; Liliental-Weber, Zuzanna; Ruvimov, Sergei; Sullivan, John P.


    The nucleation of GaN thin films on GaAs is investigated for growth at 620 "C. An rf plasma cell is used to generate chemically active nitrogen from N2. An arsenic flux is used in the first eight monolayer of nitride growth to enhance nucleation of the cubic phase. Subsequent growth does not require an As flux to preserve the cubic phase. The nucleation of smooth interfaces and GaN films with low stacking fault densities is dependent upon relative concentrations of active nitrogen species in the plasma and on the nitrogen to gallium flux ratio.

  17. Investigation of structural and optical properties of GaN on flat and porous silicon

    Abud, Saleh H.; Selman, Abbas M.; Hassan, Z.


    In this work, gallium nitride (GaN) layers were successfully grown on Flat-Si and porous silicon (PSi) using a radio frequency-magnetron sputtering system. Field emission scanning electron microscopy and atomic force microscopy images showed that the grown film on Flat-Si had smoother surface, even though there were some cracks on it. Furthermore, the X-ray diffraction measurements showed that the peak intensity of all the grown layers on PSi was higher than that of the grown layer on Flat-Si. Our detailed observation showed that PSi is a promising substrate to obtain GaN films.

  18. Molecular dynamics study of defect formation in GaN cascades

    Nord, J D; Keinonen, J; Albe, K


    Simulations of irradiation effects in compound semiconductors require interatomic potentials which describe not only the compound phases, but also the pure constituents and defects. We discuss a systematic approach based on the analytic bond-order scheme for constructing such potentials and give an example for GaN. Finally, this potential is employed for simulations of defect formation in GaN by ion irradiation for recoils in the 200 eV to 10 keV energy range. Results on the total damage production are presented and compared with other semiconductors and experiments.

  19. The use of doping spikes in GaN Gunn diodes

    Macpherson, R. F.; Dunn, G. M.


    The possibility of circumventing the difficulties of fine doping control in GaN Gunn diode devices by the substitution of a fully depleted p-type doping spike for the doping notch used to promote domain formation is explored using a Monte Carlo model. The p-type doping spike is a commonly used structure, but its potential use in GaN has not been previously evaluated. The results for a functional doping spike are compared, favorably, to those for a physically reasonable doping notch.

  20. Estimation of Hot Electron Relaxation Time in GaN Using Hot Electron Transistors

    Dasgupta, Sansaptak; Lu, Jing; Nidhi; Raman, Ajay; Hurni, Christophe; Gupta, Geetak; Speck, James S.; Mishra, Umesh K.


    In this paper, we report for the first time an estimation of hot electron relaxation time in GaN using electrical measurements. Hot electron transistors (HETs) with GaN as the base layer and different base-emitter barrier-height configurations and base thicknesses were fabricated. Common-base measurements were performed to extract the differential transfer ratio, and an exponential decay of the transfer ratio with increasing base thickness was observed. A hot electron mean free path was extracted from the corresponding exponential fitting and a relaxation time was computed, which, for low energy injection, matched well with theoretically predicted relaxation times based on longitudinal optical (LO) phonon scattering.

  1. Simulation of optimum parameters for GaN MSM UV photodetector

    Alhelfi, Mohanad A.; Ahmed, Naser M.; Hashim, M. R.; Al-Rawi, Ali Amer; Hassan, Z.


    In this study the optimum parameters of GaN M-S-M photodetector are discussed. The evaluation of the photodetector depends on many parameters, the most of the important parameters the quality of the GaN film and others depend on the geometry of the interdigited electrode. In this simulation work using MATLAB software with consideration of the reflection and absorption on the metal contacts, a detailed study involving various electrode spacings (S) and widths (W) reveals conclusive results in device design. The optimum interelectrode design for interdigitated MSM-PD has been specified and evaluated by effect on quantum efficiency and responsivity.

  2. Structural properties of undoped and doped cubic GaN grown on SiC(001)

    Martínez-Guerrero, Esteban; Bellet-Amalric, E.; Martinet, L.; Feuillet, G.; Daudin, B.


    Transmission electron microscopy and x-ray diffraction measurements reveal the presence of stacking faults ~SFs! in undoped cubic GaN thin layers. We demonstrate the importance of the defects in the interfacial region of the films by showing that the SFs act as nucleation sites for precipitates of residual impurities such as C and Si present in the GaN layers grown on SiC~001! substrates. We used the imaging secondary ion mass spectroscopy technique to locate these impurities. The systemat...

  3. Proximity Effects of Beryllium-Doped GaN Buffer Layers on the Electronic Properties of Epitaxial AlGaN/GaN Heterostructures


    properties of AlGaN/ GaN HEMTs grown on SiC sub- strates [11,15], and that these effects may vary with the proximity of the doped layer to the of Al- GaN / GaN HEMTs grown by rf-MBE on native GaN substrates. 2. Experimental Seven AlGaN/ GaN heterostructures were grown by rf-plasma assisted...buffer needs to include Be-doped GaN isolation layers in MBE-grown AlGaN/ GaN HEMTs and must be separated from the 2DEG by 200 nm to 500 nm. Acknowledgments

  4. Electrical and structural properties of GaN films and GaN/InGaN light-emitting diodes grown on porous GaN templates fabricated by combined electrochemical and photoelectrochemical etching

    Jang, Lee-Woon; Jeon, Dae-Woo [School of Advanced Materials Engineering and Research Center for Advanced Materials Development, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Polyakov, A.Y.; Govorkov, A.V. [Institute of Rare Metals, B. Tolmachevsky, 5, Moscow 119017 (Russian Federation); Sokolov, V.N. [Department of Engineering and Ecological Geology, Moscow State University, Vorobyovygory, Moscow 119991 (Russian Federation); Smirnov, N.B. [Institute of Rare Metals, B. Tolmachevsky, 5, Moscow 119017 (Russian Federation); Cho, Han-Su; Yun, Jin-Hyeon [School of Advanced Materials Engineering and Research Center for Advanced Materials Development, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Shcherbatchev, K.D. [National University of Science and Technology MISiS, Leninsky Ave. 4, Moscow 119049 (Russian Federation); Baek, Jong-Hyeob [LED R and D Division, Korea Photonics Technology Institute, Gwangju 500-779 (Korea, Republic of); Lee, In-Hwan, E-mail: [School of Advanced Materials Engineering and Research Center for Advanced Materials Development, Chonbuk National University, Jeonju 561-756 (Korea, Republic of)


    Highlights: • Porous GaN template was prepared by electrochemical and photoelectrochemical etching scheme. • InGaN/GaN light-emitting diode (LED) structure was overgrown on the etched GaN template. • Overgrown GaN films and LEDs showed lower strain and lower density of surface defects. • The overgrown LED structures showed enhanced electroluminescence efficiency. -- Abstract: Porous GaN templates were prepared by combined electrochemical etching (ECE) and back-side photoelectrochemical etching (PECE), followed by the overgrowth of GaN films and InGaN/GaN multiple quantum well (MQW) light-emitting diode (LED) structures. Structural, luminescent, and electrical properties of the GaN and LED structures were studied and compared with the properties of structures grown under the same conditions on templates not subjected to ECE–PECE treatment. Overgrowth of LED structures on the ECE–PECE templates reduced strain, cracking, and micropits, leading to increased internal quantum efficiency and light extraction efficiency. This luminescence enhancement was observed in overgrown GaN films, but was more pronounced for InGaN/GaN LED structures due to suppression of piezoelectric polarization field in QWs.

  5. Structural analysis of GaN using high-resolution X-ray diffraction at variable temperatures; Analyse struktureller Eigenschaften von GaN mittels hochaufloesender Roentgenbeugung bei variabler Messtemperatur

    Roder, C.


    The main topic of this thesis was the study of stress phenomena in GaN layers by application of high-resolution X-ray diffractometry at variable measurement temperature. For this a broad spectrum of different GaN samples was studied, which extended from bulk GaN crystals as well as thick c-plane oriented HVPE-GaN layers on c-plane sapphire over laterlaly overgrown c-plane GaN Layers on Si(111) substrates toon-polar a-plnae GaN layers on r-plane sapphire. The main topic of the measurements was the determination of the lattice parameters. Supplementarily the curvature of the waver as well as the excitonic resosance energies were studied by means of photoluminescence respectively photoreflection spectroscopy. By the measurement of the temperature-dependent lattice parameters of different GaN bulk crystals for the first time a closed set of thermal-expansion coefficients of GaN was determined from 12 to 1205 K with large accuracy. Analoguously the thermal-expansion coefficents of the substrate material sapphire were determinde over a temperature range from 10 to 1166 K.

  6. Control of residual carbon concentration in GaN high electron mobility transistor and realization of high-resistance GaN grown by metal-organic chemical vapor deposition

    He, X.G. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Zhao, D.G., E-mail: [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Jiang, D.S.; Liu, Z.S.; Chen, P.; Le, L.C.; Yang, J.; Li, X.J. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Zhang, S.M.; Zhu, J.J.; Wang, H.; Yang, H. [Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215125 (China)


    GaN films were grown by metal-organic chemical vapor deposition (MOCVD) under various growth conditions. The influences of MOCVD growth parameters, i.e., growth pressure, ammonia (NH{sub 3}) flux, growth temperature, trimethyl-gallium flux and H{sub 2} flux, on residual carbon concentration ([C]) were systematically investigated. Secondary ion mass spectroscopy measurements show that [C] can be effectively modulated by growth conditions. Especially, it can increase by reducing growth pressure up to two orders of magnitude. High-resistance (HR) GaN epilayer with a resistivity over 1.0 × 10{sup 9} Ω·cm is achieved by reducing growth pressure. The mechanism of the formation of HR GaN epilayer is discussed. An Al{sub x}Ga{sub 1−x}N/GaN high electron mobility transistor structure with a HR GaN buffer layer and an additional low-carbon GaN channel layer is presented, exhibiting a high two dimensional electron gas mobility of 1815 cm{sup 2}/Vs. - Highlights: • Influence of MOCVD parameters on residual carbon concentration in GaN is studied. • GaN layer with a resistivity over 1 × 10{sup 9} Ω·cm is achieved by reducing growth pressure. • High electron mobility transistor (HEMT) structures were prepared. • Control of residual carbon content results in HEMT with high 2-D electron gas mobility.

  7. Valentine’s Day


    <正>February 14 is a day for people who have fallen in love.On this day, these men and women give gifts(presents) and cards to each other for Valentine’s Day(情人节). This day has been popular with people in love for a long time.At first,this holiday was called Lupercalia. Then the name of the day was changed to Saint Valentine’s Day.The man named Saint Valentine was killed on February 14,270 AD,because he was a Christian(基督教徒).

  8. Roles of Ⅴ/Ⅲ ratio and mixture degree in GaN growth: CFD and MD simulation study

    Zhou An; Xiu Xiang-Qian; Zhang Rong; Xie Zi-Li; Hua Xue-Mei; Liu Bin; Han Ping


    To understand the mechanism of Gallium nitride (GaN) film growth is of great importance for their potential applications.In this paper,we investigate the growth behavior of the GaN film by combining computational fluid dynamics (CFD) and molecular dynamics (MD) simulations.Both of the simulations show that Ⅴ/Ⅲ mixture degree can have important impacts on the deposition behavior,and it is found that the more uniform the mixture is,the better the growth is.Besides,by using MD simulations,we illustrate the whole process of the GaN growth.Furthermore,we also find that the Ⅴ/Ⅲ ratio can affect the final roughness of the GaN film.When the Ⅴ/Ⅲ ratio is high,the surface of final GaN film is smooth.The present study provides insights into GaN growth from the macroscopic and microscopic views,which may provide some suggestions on better experimental GaN preparation.

  9. Growth optimization and characterization of GaN epilayers on multifaceted (111) surfaces etched on Si(100) substrates

    Ansah-Antwi, KwaDwo Konadu, E-mail:; Chua, Soo Jin [Institute of Materials Research and Engineering (IMRE), A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis # 08-03, Singapore 138634 (Singapore); Department of Electrical and Computer Engineering, National University of Singapore, E4-5-45, 4 Engineering Drive 3, Singapore 117576 (Singapore); Soh, Chew Beng [Singapore Institute of Technology, 10 Dover Drive, Singapore 138683 (Singapore); Liu, Hongfei [Institute of Materials Research and Engineering (IMRE), A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis # 08-03, Singapore 138634 (Singapore)


    The four nearest Si(111) multifaceted sidewalls were exposed inside an array of 3 μm-wide square holes patterned on an Si(100) substrate, and this patterned Si(100) substrate was used as a substrate for the deposition of a gallium nitride (GaN) epilayer. Subsequently the effect that the growth pressure, the etched-hole profiles, and the etched-hole arrangement had upon the quality of the as-grown GaN was investigated. The coalescence of the as-grown GaN epilayer on the exposed Si(111) facets was observed to be enhanced with reduced growth pressure from 120 to 90 Torr. A larger Si(001) plane area at the bottom of the etched holes resulted in bidirectional GaN domains, which resulted in poor material quality. The bidirectional GaN domains were observed as two sets of six peaks via a high-resolution x-ray diffraction phi scan of the GaN(10-11) reflection. It was also shown that a triangular array of etched holes was more desirable than square arrays of etched holes for the growth high-quality and continuous GaN films.

  10. A study of the red-shift of a neutral donor bound exciton in GaN nanorods by hydrogenation

    Park, Byung-Guon; Lee, Sang-Tae; Reddeppa, Maddaka; Kim, Moon-Deock; Oh, Jae-Eung; Lee, Sang-Kwon


    In this paper we account for the physics behind the exciton peak shift in GaN nanorods (NRs) due to hydrogenation. GaN NRs were selectively grown on a patterned Ti/Si(111) substrate using plasma-assisted molecular beam epitaxy, and the effect of hydrogenation on their optical properties was investigated in detail using low-temperature photoluminescence measurements. Due to hydrogenation, the emissions corresponding to the donor-acceptor pair and yellow luminescence in GaN NRs were strongly suppressed, while the emission corresponding to the neutral to donor bound exciton (D0X) exhibited red-shift. Thermal annealing of hydrogenated GaN NRs demonstrated the recovery of the D0X and deep level emission. To determine the nature of the D0X peak shift due to hydrogenation, comparative studies were carried out on various diameters of GaN NRs, which can be controlled by different growth conditions and wet-etching times. Our experimental results reveal that the D0X shift depends on the diameter of the GaN NRs after hydrogenation. The results clearly demonstrate that the hydrogenation leads to band bending of GaN NRs as compensated by hydrogen ions, which causes a red-shift in the D0X emission.

  11. Growth of GaN on sapphire via low-temperature deposited buffer layer and realization of p-type GaN by Mg doping followed by low-energy electron beam irradiation

    Amano, Hiroshi [Department of Electrical Engineering and Computer Science, Venture Business Laboratory, Akasaki Research Center, Nagoya University (Japan)


    This is a personal history of one of the Japanese researchers engaged in developing a method for growing GaN on a sapphire substrate, paving the way for the realization of smart television and display systems using blue LEDs. The most important work was done in the mid to late 1980s. The background to the author's work and the process by which the technology enabling the growth of GaN and the realization of p-type GaN was established are reviewed. (copyright 2015 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  12. The photocatalytic properties of hollow (GaN)1-x(ZnO)x composite nanofibers synthesized by electrospinning

    Wang, Ding; Zhang, Minglu; Zhuang, Huaijuan; Chen, Xu; Wang, Xianying; Zheng, Xuejun; Yang, Junhe


    (GaN)1-x(ZnO)x composite nanofibers with hollow structure were prepared by initial electrospinning, and the subsequent calcination and nitridation. The structure and morphology characteristics of samples were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The characterization results showed the phase transition from ZnGa2O4 to (GaN)1-x(ZnO)x solid-solution under ammonia atmosphere. The preparation conditions were explored and the optimum nitridation temperature and holding time are 750 °C and 2 h, respectively. The photocatalytic properties of (GaN)1-x(ZnO)x with different Ga:Zn atomic ratios were investigated by degrading Rhodamine B under the visible light irradiation. The photocatalytic activity sequence is (GaN)1-x(ZnO)x (Ga:Zn = 1:2) > (GaN)1-x(ZnO)x (Ga:Zn = 1:3) > ZnO nanofibers > (GaN)1-x(ZnO)x (Ga:Zn = 1:4) > (GaN)1-x(ZnO)x (Ga:Zn = 1:1). The photocatalytic mechanism of the (GaN)1-x(ZnO)x hollow nanofibers was further studied by UV-vis diffuse reflectance spectra. The excellent photocatalytic performance of (GaN)1-x(ZnO)x hollow nanofibers was attributed to the narrow band gap and high surface area of porous nanofibers with hollow structure.

  13. Structural and optical properties of ZnO nanorods grown chemically on sputtered GaN buffer layers

    Nandi, R.; Joshi, Pranav [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Singh, Devendra; Mohanta, Pravanshu [Centre for Research in Nanotechnology and Science, Indian Institute of Technology Bombay, Mumbai 400076 (India); Srinivasa, R.S. [Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400076 (India); Major, S.S., E-mail: [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India)


    ZnO nanorods were grown on 200 nm thick sputtered ZnO and GaN buffer layers on quartz substrates by chemical bath deposition. Field emission scanning electron microscopy and X-ray diffraction studies show that the ZnO nanorods on GaN buffer layer possess larger diameter and smaller lengths and are vertically misaligned, compared to those grown on ZnO buffer layer. These differences are attributed to lack of complete c-axis orientation of crystallites in GaN buffer layer, its lattice mismatch with that of ZnO and a hindered nucleation process of ZnO on GaN surface, owing to a finite nucleation barrier and limited surface diffusion. Photoluminescence spectrum of ZnO nanorods on GaN buffer layer, however, exhibits a much stronger near-band-edge luminescence and drastically suppressed defect luminescence compared to the luminescence spectrum of the nanorods grown on ZnO buffer layer. Deconvolution of the photoluminescence peaks and Raman studies indicate significant reduction of oxygen vacancies and gallium incorporation in the ZnO nanorods grown on GaN buffer layer. These observations suggest the possibility of exchange reaction mediated by the aqueous medium, particularly during the initial stages of growth. - Highlights: • ZnO nanorods were grown on sputtered GaN buffer layer deposited on quartz. • ZnO nanorods on polycrystalline GaN show limited vertical alignment of c-axis. • ZnO nanorods on GaN show high band edge and negligible defect luminescence. • Raman and photoluminescence studies indicate solution mediated interface reaction.

  14. Effect of residual stress on the microstructure of GaN epitaxial films grown by pulsed laser deposition

    Wang, Haiyan; Wang, Wenliang; Yang, Weijia; Zhu, Yunnong; Lin, Zhiting; Li, Guoqiang


    The stress-free GaN epitaxial films have been directly grown by pulsed laser deposition (PLD) at 850 °C, and the effect of different stress on the microstructure of as-grown GaN epitaxial films has been explored in detail. The as-grown stress-free GaN epitaxial films exhibit very smooth surface without any particles and grains, which is confirmed by the smallest surface root-mean-square roughness of 2.3 nm measured by atomic force microscopy. In addition, they also have relatively high crystalline quality, which is proved by the small full-width at half maximum values of GaN(0002) and GaN (10 1 bar 2) X-ray rocking curves as 0.27° and 0.68°, respectively. However, when the growth temperature is lower or higher than 850 °C, internal or thermal stress would be increased in as-grown GaN epitaxial films. To release the larger stress, a great number of dislocations are generated. Many irregular particulates, hexagonal GaN gains and pits are therefore produced on the films surface, and the crystalline quality is greatly reduced consequently. This work has demonstrated the direct growth of stress-free GaN epitaxial films with excellent surface morphology and high crystalline quality by PLD, and presented a comprehensive study on the origins and the effect of stress in GaN layer. It is instructional to achieve high-quality nitride films by PLD, and shows great potential and broad prospect for the further development of high-performance GaN-based devices.

  15. Day Care Centers

    Department of Homeland Security — This database contains locations of day care centers for 50 states and Washington D.C. and Puerto Rico. The dataset only includes center based day care locations...

  16. Analysis of threading dislocations in void shape controlled GaN re-grown on hexagonally patterned mask-less GaN

    Ali, M.; Romanov, A. E.; Suihkonen, S.; Svensk, O.; Sintonen, S.; Sopanen, M.; Lipsanen, H.; Nevedomsky, V. N.; Bert, N. A.; Odnoblyudov, M. A.; Bougrov, V. E.


    In this article, we analyze the behavior of threading dislocations in GaN layers re-grown on hexagonally patterned mask-less GaN. The growth mode of the material with patterned hexagonal morphology changes with the diameter and the periodicity of the hexagonal patterns. The growth mode directly affects the shape of the voids that are formed in this kind of lateral epitaxy. Transmission electron microscopy has been used to study threading dislocations in GaN layers with voids having different sizes and sidewall angles. The results show that a significant number of threading dislocations near the tapered void's surface undergo a 90° reorientation in their propagation trajectory whereas almost no dislocations bend in the case of smaller voids having more vertical sidewalls. Different types of dislocations in the vicinity of the voids have also been identified using the invisibility g·b criteria. The full width at half maximum values for XRD ω-scan recorded in (002) reflection drop from 256″ to 181″ as the void sidewall inclination changes from 85° to 60°. A similar dropping trend in the full width at half maximum values for asymmetric diffraction reflections has also been observed.

  17. Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces; Rastertunnelmikroskopie und -spektroskopie an GaN- und InGaN-Oberflaechen

    Krueger, David


    Optelectronic devices based on gallium nitride (GaN) and indium gallium nitride (InGaN) are in the focus of research since more than 20 years and still have great potential for optical applications. In the first part of this work non-polar surfaces of GaN are investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). In SEM and AFM, the (1 anti 100)- and especially the (anti 2110)-plane are quite corrugated. For the first time, the (anti 2110)-plane of GaN is atomically resolved in STM. In the second part InGaN quantum dot layers are investigated by X-ray photoelectron spectroscopy (XPS), scanning tunneling spectroscopy (STS) and STM. The STMmeasurements show the dependency of surface morphology on growth conditions in the metalorganic vapour phase epitaxy (MOVPE). Nucleation, a new MOVPE-strategy, is based on phase separations on surfaces. It is shown that locally varying density of states and bandgaps can be detected by STS, that means bandgap histograms and 2D-bandgap-mapping. (orig.)

  18. Hydride-vapor-phase epitaxial growth of highly pure GaN layers with smooth as-grown surfaces on freestanding GaN substrates

    Fujikura, Hajime; Konno, Taichiro; Yoshida, Takehiro; Horikiri, Fumimasa


    Thick (20-30 µm) layers of highly pure GaN with device-quality smooth as-grown surfaces were prepared on freestanding GaN substrates by using our advanced hydride-vapor-phase epitaxy (HVPE) system. Removal of quartz parts from the HVPE system markedly reduced concentrations of residual impurities to below the limits of detection by secondary-ion mass spectrometry. Appropriate gas-flow management in the HVPE system realized device-quality, smooth, as-grown surfaces with an excellent uniformity of thickness. The undoped GaN layer showed insulating properties. By Si doping, the electron concentration could be controlled over a wide range, down to 2 × 1014 cm-3, with a maximum mobility of 1150 cm2·V-1·s-1. The concentration of residual deep levels in lightly Si-doped layers was in the 1014 cm-3 range or less throughout the entire 2-in. wafer surface. These achievements clearly demonstrate the potential of HVPE as a tool for epitaxial growth of power-device structures.

  19. Is day surgery safe?

    Majholm, Birgitte; Engbæk, J; Bartholdy, Jens


    Day surgery is expanding in several countries, and it is important to collect information about quality. The aim of this study was to assess morbidity and unanticipated hospital visits 0-30 days post-operatively in a large cohort.......Day surgery is expanding in several countries, and it is important to collect information about quality. The aim of this study was to assess morbidity and unanticipated hospital visits 0-30 days post-operatively in a large cohort....

  20. Tehnical day: solar energy

    Carli, Barbara


    This dissertation presents an example of planning and carrying out a technical activity day in the field of solar energy in primary school grades 7 and 9. Firstly, we briefly present technical activity days, the goals and criteria for the planning of technical days, and the topics and devices connected to the technical day in question and were needed in the execution of the experiments. We have selected four simple experiments in the field of solar energy and prepared the needed worksheets fo...

  1. April Fools’ Day



    April Fools’ Day,the day when mischief-makers(恶作剧的人)are ever so indulged(纵容),falls on April 1 every year.On that day,various pranks(恶作剧)are played on one another,and everybody has to be

  2. A Day to Celebrate


    Participating countries at the 2010 World Expo in Shanghai can choose a day as their National Pavilion Day.The day is usually celebrated with ceremonies and performances,which bring the nation’s culture and its character to life.

  3. Valentine’s Day



    Valentine’s Day, which falls on February 14, is one of the most popular festivals of western society and even the whole world. It is a day for lovers, a day when people present chocolates, cards and candies to their beloved (心爱的人).

  4. Evaluation of freestanding GaN as an alpha and neutron detector

    Mulligan, Padhraic; Wang, Jinghui; Cao, Lei, E-mail:


    The wide bandgap (3.39) eV and large dislocation energy of the III–V semiconductor gallium nitride (GaN) make this a desirable material for charged particle spectroscopy in high temperature, high radiation environments. While other research groups have established that charged particle detectors can be fabricated from high quality, thin films of molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) grown GaN, this work demonstrates the feasibility of ionizing radiation detectors created from significantly thicker freestanding n-type GaN, grown via hydride vapor phase epitaxy (HVPE). Detectors were fabricated by depositing Ni/Au pads on n-type GaN, forming a Schottky barrier diode. Capacitance–voltage measurements on the detectors showed an intrinsic carrier concentration in the range of 10{sup −16} cm{sup −3}–10{sup –15} cm{sup −3}, and indicated an inhomogeneous distribution between diodes on the same wafer. The radiation sensitivity of the fabricated detectors was analyzed using alpha particles from an {sup 241}Am source. Charge collection efficiency (CCE) calculations from these experiments indicate an efficiency of 100 percent. The detectors were also successfully used to detect neutron induced charged particles using a Li{sub 2}O foil in a neutron beam.

  5. 10kW TWT Transition to GaN IRE


    Office. Phase III of this effort would align to a NISE 219 project due to the amount of funding required for thermal modeling and analysis, FEA...done to prepare the 10kW TWT transition to GaN for sponsorship by a Program Office. Phase III of this effort would align to a NISE 219 project due to

  6. Strain effect on optical polarization properties of a -plane GaN on r -plane sapphire

    Wu, Chao; Yu, Tongjun; Tao, Renchun; Jia, Chuanyu; Yang, Zhijian; Zhang, Guoyi [State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, 100871 Beijing (China)


    In this study, the optical polarization properties under varying strains in a-plane GaN were investigated. The valence band (VB) structure for a-plane GaN is derived from the effective-mass Hamiltonian based on k.p perturbation theory. The relative oscillator strength (ROS) calculations of the transitions related to the top three VBs near {gamma} point are applied to analyzing the optical polarized properties. For a-plane GaN, the main components of the first, the second and the third VBs are vertical stroke Y right angle -like (y-axis //[1 anti 100]), vertical stroke Z right angle -like (z-axis //[0001]) and vertical stroke X right angle -like (x-axis //[11 anti 20]) states, respectively. Under small compressive strain along c-axis, the polarization degree increases with compressive strain increasing. According to X-ray diffraction (XRD) scans and Raman backscattering spectra, both the in-plane and out-plane strains were evaluated. Polarized photoluminescence (PL) is employed to obtain the polarization degree. The experimental results of a-plane GaN samples under different strains showed good accordance with our theoretical calculations (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Nanopipes in GaN: photo-etching and TEM study

    Lazar, S.; Weyher, J.L.; Macht, L.; Tichelaar, F.D.; Zandbergen, H.W.


    Photochemical (PEC) etching and transmission electron microscopy (TEM) have been used to study the defects in hetero-epitaxial GaN layers. TEM proved that PEC etching reveals not only dislocations but also nanopipes in the form of protruding, whisker-like etch features. It is shown by diffraction co

  8. Optical excitation and external photoluminescence quantum efficiency of Eu3+ in GaN

    de Boer, W.D.A.M.; McGonigle, C.; Gregorkiewicz, T.; Fujiwara, Y.; Stallinga, P.


    We investigate photoluminescence of Eu-related emission in a GaN host consisting of thin layers grown by organometallic vapor-phase epitaxy. By comparing it with a reference sample of Eu-doped Y2O3, we find that the fraction of Eu3+ ions that can emit light upon optical excitation is of the order of

  9. Electron field emission from nanostructured surfaces of GaN and AlGaN

    Evtukh, A.; Litovchenko, V.; Semenenko, M.; Gorbanyuk, T.; Grygoriev, A. [Institute of Semiconductor Physics, 41 prospekt Nauki, 03028 Kiev (Ukraine); Yilmazoglu, O.; Hartnagel, H.; Pavlidis, D. [Technische Universitaet Darmstadt, Institut fuer Hochfrequenztechnik, Merckstr. 25, 64283 Darmstadt (Germany)


    The possibility of high frequency electromagnetic wave generation by field emission based devices has great interest. The wide bandgap materials GaN and AlGaN are very promising for these applications due to low electron affinity and the existence of satellite valleys in conduction band. The results of investigations of the peculiarities of electron field emission from nanostructured surfaces of GaN and AlGaN are presented. Multilayer GaN and AlGaN structures with various levels of layer doping on sapphire and bulk GaN substrates were used as initial wafers. The surface of the upper layers was nanostructured by photoelectrochemical etching in water solution of KOH. Intensive electron field emission into vacuum was observed and explained by low electron affinity and electric field enhancement on surface nanowires. A decrease of the slope in the Fowler-Nordheim characteristics was revealed. The changing slope suggests a lowering of effective work function. It is caused by electron heating and transfer into an upper satellite valley with lower electron affinity. A theory was developed for the observed phenomena and interpretation of results. It is based on electron intervalley transition upon heating and on energy band reconstruction of the surface of the nanowires due to quantum size-confinement effect. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Cu Ions Irradiation Impact on Structural and Optical Properties of GaN Thin Film

    Shah, A.; Husnain, G.; Ahmad, Ishaq; Mahmood, Arshad


    Epitaxial grown Gallium nitride (GaN) thin film on sapphire was irradiated with Cu ions at various fluences (5×1014, 1 ×1015 and 5×1015cm-2). The level of lattice disorder, as measured by Rutherford backscattering spectrometry and channeling (RBS/C), gradually increases with the increasing of ions fluence. Lattice amorphization is observed for the sample irradiated with fluence of 5×1015cm-2 which is also confirmed by X-ray diffractometer (XRD) analysis. It was found that both Raman modes of GaN layer clearly shifted with Cu+ fluences. Both Raman and X-ray analyses explore that Cu atom substituted into Ga sites. Atomic force microscopy (AFM) images show the irradiated GaN surface roughness increases with the increasing ions fluence. The UV-visible transmittance spectrum and ellipsometric measurements show a decrease in the band gap value after irradiation of Cu ions in the GaN film. Moreover, the optical constants (n and k) of the films vary with the increasing of Cu ion fluences.

  11. MBE Growth and Characterization of Zincblende GaN and GaN/AlN Structures


    This Program includes fundamental studies of Molecular beam epitaxial ( MBE ) growth of GaN and its related alloys and heterostructures. In additions...physics of MBE growth , and the optical and electrical properties for GaN-based device application. 1

  12. Electrical properties of Si-doped GaN prepared using pulsed sputtering

    Arakawa, Yasuaki; Ueno, Kohei; Imabeppu, Hideyuki; Kobayashi, Atsushi; Ohta, Jitsuo; Fujioka, Hiroshi


    In this study, we investigated the basic electrical properties of Si-doped wurtzite GaN films prepared using a low-temperature pulsed sputtering deposition (PSD) process. We found that the electron concentration can be controlled in the range between 1.5 × 1016 and 2.0 × 1020 cm-3. For lightly Si-doped GaN ([Si] = 2.1 × 1016 cm-3), the room temperature (RT) electron mobility was as high as 1008 cm2 V-1 s-1, which was dominantly limited by polar optical phonon scattering. Moreover, we found that heavily Si-doped GaN prepared using PSD exhibited an RT mobility as high as 110 cm2 V-1 s-1 at an electron concentration of 2 × 1020 cm-3, which indicated that the resistivity of this film was almost as small as those of typical transparent conductive oxides such as indium tin oxide. At lower temperatures, the electron mobility increased to 1920 cm2 V-1 s-1 at 136 K, and the temperature dependence was well explained by conventional scattering models. These results indicate that Si-doped GaN prepared using PSD is promising not only for the fabrication of GaN-based power devices but also for use as epitaxial transparent electrode materials for nitride based optical devices.

  13. Modeling and Simulation of a Gallium Nitride (GaN) Betavoltaic Energy Converter


    technologies, nuclear materials detection, accelerator shielding, and dose/energy deposition in materials for medical therapies . An electron beam with...semiconductor devices have the potential to improve the efficiency of direct energy conversion and indirect energy conversion isotope batteries, making...offering higher- energy-conversion efficiency than 2-dimensional geometries. 15. SUBJECT TERMS GaN, betavoltaic, device simulation, isotope power source

  14. Effect of TMBi supply on low-temperature MOVPE growth behavior of GaN

    Saidi, C.; Chaaben, N.; Laifi, J.; Sekrafi, T. [Unité de Recherche sur les Hétéro-Epitaxies et Applications, Faculté des Sciences de Monastir, Avenue de l’Environnement, 5019 Monastir (Tunisia); Tottereau, O. [Centre de Recherche sur l’Hétéro-Epitaxie et Ses Applications, Centre National de la Recherche Scientifique, CRHEA-CNRS, Rue Bernard Grégory, F-06560 Valbonne, Sophia Antipolis (France); Bchetnia, A.; El Jani, B. [Unité de Recherche sur les Hétéro-Epitaxies et Applications, Faculté des Sciences de Monastir, Avenue de l’Environnement, 5019 Monastir (Tunisia)


    Highlights: • We examined the Bi doping effect on GaN layers properties, grown by LT-MOVPE. • No obvious dependence of growth rate with TMBi flow rate. • TMBi flow rate addition resulted in a reduction of reflectivity oscillation mean value. • We note the appearance of islands and columns containing Bi on layers surface. • While there is a decrease in surface roughness suggesting Bi surfactant effect. - Abstract: Undoped GaN and diluted GaNBi alloys were grown on (0 0 0 1) sapphire substrate by metal–organic vapor phase epitaxy (MOVPE) at 480 °C. By using in-situ laser reflectometry, it is found that the increase of TMBi flow rate leads to a reduction of the average value of reflectivity oscillations. Scanning electron microscopy (SEM) images gave a clear observation of the TMBi increasing amount effect on the surface morphology. The appearance of different structure (islands and columns) on GaN surface could be responsible to the reduction of the reflectivity oscillations average value. The energy dispersive X-ray (EDX) analysis showed that the observed structures were only composed of Bi compared to the flat GaN surface. Moreover, the surface morphology between islands and columns is improved when we increase the TMBi flow rate. This improvement is consistent with the decrease of root mean square (RMS) roughness, as measured by atomic force microscopy (AFM)

  15. Plasmon enhanced green GaN light-emitting diodes - Invited paper

    Ou, Haiyan; Fadil, Ahmed; Iida, Daisuke

    in spectral design, more compact etc. TheIII-nitride (GaN, InNetc.) semiconductors are attracting a lot of research effort because the combination of both could emit light with wavelength range from UV to infrared. Basically one material platform could provide all the solutions to light sources.However huge...

  16. Fabrication and Characterization of Mg-Doped GaN Nanowires

    ZHANG Dong-Dong; XUE Cheng-Shan; ZHUANG Hui-Zhao; HUANG Ying-Long; WANG Zou-Ping; WANG Ying; GUO Yong-Fu


    Mg-doped GaN nanowires have been synthesized by ammoniating Ga2O3 films doped with Mg under flowing ammonia atmosphere at 850℃. The Mg-doped GaN nanowires are characterized by x-ray diffraction (XRD),scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM) and photo-luminescence (PL). The results demonstrate that the nanowires are single crystalline with hexagonal wurzite structure. The diameters of the nanowires are 20-30nm and the lengths are 50-100μm. The GaN nanowires show three emission bands with well-defined PL peak at 3.45 eV, 3.26eV, 2.95 eV, respectively. The large distinct blueshift of the bandgap emission can be attributed to the Burstein-Moss effect. The peak at 3.26eV represents the transition from the conduction-band edge to the acceptor level AM (acceptor Mg). The growth mechanism of crystalline GaN nanowires is discussed briefly.

  17. Deep level defect in Si-implanted GaN n +-p junction


    The results of deep level transient spectroscopy (DLTS) experiments on GaN junctions, fabricated by silicon implantation, were discussed. An unusual appearance of a minority peak in the majority carrier DLTS spectra within the interfacial region of the junctions was observed. The presence of this minority peak suggested a high concentration of a deep level defect within the interfacial region.

  18. GaN nano-pyramid arrays as an efficient photoelectrode for solar water splitting

    Hou, Y.; Yu, X.; Syed, Z. Ahmed; Shen, S.; Bai, J.; Wang, T.


    A prototype photoelectrode has been fabricated using a GaN nano-pyramid array structure grown on a cost-effective Si (111) substrate, demonstrating a significant improvement in performance of solar-powered water splitting compared with any planar GaN photoelectrode. Such a nano-pyramid structure leads to enhanced optical absorption as a result of a multi-scattering process which can effectively produce a reduction in reflectance. A simulation based on a finite-difference time-domain approach indicates that the nano-pyramid architecture enables incident light to be concentrated within the nano-pyramids as a result of micro-cavity effects, further enhancing optical absorption. Furthermore, the shape of the nano-pyramid further facilitates the photo-generated carrier transportation by enhancing a hole-transfer efficiency. All these features as a result of the nano-pyramid configuration lead to a large photocurrent of 1 mA cm-2 under an illumination density of 200 mW cm-2, with a peak incident photon-to-current conversion efficiency of 46.5% at ˜365 nm, around the band edge emission wavelength of GaN. The results presented are expected to pave the way for the fabrication of GaN based photoelectrodes with a high energy conversion efficiency of solar powered water splitting.

  19. CFD and reaction computational analysis of the growth of GaN by HVPE method

    Kempisty, P.; Łucznik, B.; Pastuszka, B.; Grzegory, I.; Boćkowski, M.; Krukowski, S.; Porowski, S.


    GaCl synthesis reaction during hydride vapor phase epitaxy (HVPE) growth of GaN in horizontal flow reactor has been analyzed using computerized fluid dynamics (CFD) and molecular estimates of the reaction rates. Finite element code FIDAP (commercially available from Fluent Inc.) [Fidap User Manual, Fluent Inc. [1

  20. Density-dependent electron transport and precise modeling of GaN high electron mobility transistors

    Bajaj, Sanyam, E-mail:; Shoron, Omor F.; Park, Pil Sung; Krishnamoorthy, Sriram; Akyol, Fatih; Hung, Ting-Hsiang [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Reza, Shahed; Chumbes, Eduardo M. [Raytheon Integrated Defense Systems, Andover, Massachusetts 01810 (United States); Khurgin, Jacob [Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Rajan, Siddharth [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Department of Material Science and Engineering, The Ohio State University, Columbus, Ohio 43210 (United States)


    We report on the direct measurement of two-dimensional sheet charge density dependence of electron transport in AlGaN/GaN high electron mobility transistors (HEMTs). Pulsed IV measurements established increasing electron velocities with decreasing sheet charge densities, resulting in saturation velocity of 1.9 × 10{sup 7 }cm/s at a low sheet charge density of 7.8 × 10{sup 11 }cm{sup −2}. An optical phonon emission-based electron velocity model for GaN is also presented. It accommodates stimulated longitudinal optical (LO) phonon emission which clamps the electron velocity with strong electron-phonon interaction and long LO phonon lifetime in GaN. A comparison with the measured density-dependent saturation velocity shows that it captures the dependence rather well. Finally, the experimental result is applied in TCAD-based device simulator to predict DC and small signal characteristics of a reported GaN HEMT. Good agreement between the simulated and reported experimental results validated the measurement presented in this report and established accurate modeling of GaN HEMTs.

  1. GaN Power Stage for Switch-mode Audio Amplification

    Ploug, Rasmus Overgaard; Knott, Arnold; Poulsen, Søren Bang


    Gallium Nitride (GaN) based power transistors are gaining more and more attention since the introduction of the enhancement mode eGaN Field Effect Transistor (FET) which makes an adaptation from Metal-Oxide Semiconductor (MOSFET) to eGaN based technology less complex than by using depletion mode Ga...

  2. Green high-power tunable external-cavity GaN diode laser at 515 nm

    Chi, Mingjun; Jensen, Ole Bjarlin; Petersen, Paul Michael


    A 480 mW green tunable diode laser system is demonstrated for the first time to our knowledge. The laser system is based on a GaN broad-area diode laser and Littrow external-cavity feedback. The green laser system is operated in two modes by switching the polarization direction of the laser beam ...

  3. GaN C-band HPA for phased-array applications

    Wanum, M. van; Hek, A.P. de; Vliet, F.E. van


    In the UMS GH25-10 GaN MMIC technology a Cband high power amplifier (HPA) has been realized. The current design is primarily intended for use in a space-based SAR system with a center frequency of 5.4 GHz and a sweep bandwidth of 100 MHz. To enable reuse of the amplifier in other radar systems such

  4. Design and analysis of vertical-channel gallium nitride (GaN) junctionless nanowire transistors (JNT).

    Seo, Jae Hwa; Yoon, Young Jun; Lee, Hwan Gi; Yoo, Gwan Min; Jo, Young-Woo; Son, Dong-Hyeok; Lee, Jung-Hee; Cho, Eou-Sik; Cho, Seongjae; Kang, In Man


    Vertical-channel gallium nitride (GaN) junctionless nanowire transistor (JNT) has been designed and characterized by technology computer-aided design (TCAD) simulations. Various characteristics such as wide bandgap, strong polariztion field, and high electron velocity make GaN one of the attractive materials in advanced electronics in recent times. Nanowire-structured GaN can be applicable to various transistors for enhanced electrical performances by its geometrical feature. In this paper, we analyze the direct-current (DC) characteristics depending on various channel doping concentrations (N(ch)) and nanowire radii (R(NW)). Furthermore, the radio-frequency (RF) characteristics under optimized conditions are extracted by small-signal equivalent circuit modeling. For the optimally designed vertical GaN JNT demonstrated on-state current (I(on)) of 345 μA/μm and off-state current (I(off)) of 3.7 x 10(-18) A/μm with a threshold voltage (V(t)) of 0.22 V, and subthreshold swing (S) of 68 mV/dec. Besides, f(T) and f(max) under different operating conditions (gate voltage, V(GS)) have been obtained.

  5. GaN CVD Reactions: Hydrogen and Ammonia Decomposition and the Desorption of Gallium

    Bartram, Michael E.; Creighton, J. Randall


    Isotopic labeling experiments have revealed correlations between hydrogen reactions, Ga desorption, and ammonia decomposition in GaN CVD. Low energy electron diffraction (LEED) and temperature programmed desorption (TPD) were used to demonstrate that hydrogen atoms are available on the surface for reaction after exposing GaN(0001) to deuterium at elevated temperatures. Hydrogen reactions also lowered the temperature for Ga desorption significantly. Ammonia did not decompose on the surface before hydrogen exposure. However, after hydrogen reactions altered the surface, N15H3 did undergo both reversible and irreversible decomposition. This also resulted in the desorption of N2 of mixed isotopes below the onset of GaN sublimation, This suggests that the driving force of the high nitrogen-nitrogen bond strength (226 kcal/mol) can lead to the removal of nitrogen from the substrate when the surface is nitrogen rich. Overall, these findings indicate that hydrogen can influence G-aN CVD significantly, being a common factor in the reactivity of the surface, the desorption of Ga, and the decomposition of ammonia.

  6. Lanthanide impurity level location in GaN, AlN, and ZnO

    Dorenbos, P.; Van der Kolk, E.


    A method that has proven succesful in locating the energy levels of divalent and trivalent lanthanide ions (Ce, Pr,..., Eu,...Yb, Lu) in wide band gap inorganic compounds like YPO4 and CaF2 is applied to locate lanthanide levels in the wideband semiconductors GaN, AlN, their solid solutions AlxGa1-x

  7. Location of lanthanide impurity levels in the III-V semiconductor GaN

    Dorenbos, P.; Van der Kolk, E.


    Knowledge from lanthanide spectroscopy on wide band gap (6–10 eV) inorganic compounds is used to understand and predict optical and electronic properties of the lanthanides in the III-V semiconductor GaN. For the first time the location of the 4fn ground state energy of each divalent and trivalent l

  8. Evaluation of the influence mode on the CVC GaN HEMT using numerical modeling

    Parnes, Ya M.; Tikhomirov, V. G.; Petrov, V. A.; Gudkov, A. G.; Marzhanovskiy, I. N.; Kukhareva, E. S.; Vyuginov, V. N.; Volkov, V. V.; Zybin, A. A.


    Done numerically simulated the effects of certain modes of operation on the CVC of field microwave transistors on the basis of heterostructures AlGaN / GaN (HEMT). The results of these studies suggest the possibility of quite efficient use of numerical simulation for the development of HEMT microwave transistors allowing for the real instrument designs.

  9. GaN IMPATT diode: a photo-sensitive high power terahertz source

    Mukherjee, Moumita; Mazumder, Nilraton; Roy, Sitesh Kumar; Goswami, Kushalendu


    The prospects of wurtzite phase single-drift-region (SDR), flat and single-low-high-low (SLHL) type GaN IMPATT devices as terahertz sources are studied through a simulation experiment. The study indicates that GaN IMPATT diodes are capable of generating high RF power (at least 2.5 W) at around 1.45 THz with high efficiency (17-20%). The superior electronic properties of GaN make this a promising candidate for IMPATT operation in the THz regime, unapproachable by conventional Si, GaAs and InP based IMPATT diodes. The effect of parasitic series resistance on the THz performance of the device is further simulated. It is interesting to note that the presence of a charge bump in a flatly doped SDR structure reduces the value of parasitic series resistance by 22%. The effects of photo- illumination on the devices are also investigated using a modified double iterative simulation technique. Under photo-illumination (i) the negative conductance and (ii) the negative resistance of the devices (both flat and SLHL) decrease, while the frequency of operation and the device quality factor shift upwards. However, the upward shift in operating frequency is found to be more (~16 GHz) in the case of the SLHL SDR IMPATT device. The study indicates that GaN IMPATT is a promising opto-sensitive high power THz source.

  10. Tavatu juhtum / Toomas Rein, Helle Gans, Leonhard Lapin ; interv. Reet Varblane

    Rein, Toomas, 1940-


    Arhitektid Toomas Rein ja Leonhard Lapin ning sisearhitekt Helle Gans meenutavad Valgevene näidiskolhoosile Rassvet projekteeritud lasteaeda, mis valmis 1987. aastal. Kompleks pälvis 1987. a. NSVL Arhitektide Liidu preemia ja üleliidulise ametiühingupreemia

  11. Treatment of Chronic Bronchitis with Modified Ma Xing Shi Gan Tang and Er Chen Tang

    朱颖; 刘晓东


    @@ Chronic bronchitis is a disease commonly seen in the clinic. The authors have treated 78 cases of the disease with modified Ma Xing Shi Gan Tang (麻杏石甘汤 Decoction of Ephedra, Armeniacae Amarum, Glycyrrhizae and Gypsum Fibrosum) plus Er Chen Tang (二陈汤 Two Old Drugs Decoction). The results were satisfactory and reported as follows.

  12. GaN growth on silane exposed AlN seed layers

    Ruiz-Zepeda, F. [Posgrado en Fisica de Materiales, Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Km. 107 Carret, Tijuana-Ensenada, C.P. 22860, Ensenada, B.C. (Mexico); Contreras, O. [Centro de Ciencias de la Materia Condesada, Universidad Nacional Autonoma de Mexico, Apdo. Postal 356, C.P. 22800, Ensenada, B.C. (Mexico); Dadgar, A.; Krost, A. [Otto-von-Guericke-Universitaet Magdeburg, FNW-IEP, Universitaetsplatz 2, 39106 Magdeburg (Germany)


    The microstructure and surface morphology of GaN films grown on AlN seed layers exposed to silane flow has been studied by TEM and AFM. The epilayers were grown on silicon(111) substrates by MOCVD. The AlN seed layer surface was treated at different SiH{sub 4} exposure times prior to the growth of the GaN film. A reduction in the density of threading dislocations is observed in the GaN films and their surface roughness is minimized for an optimal SiH{sub 4} exposure time between 75-90 sec. At this optimal condition a step-flow growth mode of GaN film is predominant. The improvement of the surface and structure quality of the epilayers is observed to be related to an annihilation process of threading dislocations done by SiN{sub x} masking. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Fabrications and application of single crystalline GaN for high-performance deep UV photodetectors

    Velazquez, R.; Rivera, M.; Feng, P., E-mail: [Department of Physics, College of Natural Sciences, University of Puerto Rico, San Juan, 00936-8377, PR/USA (Puerto Rico); Aldalbahi, A. [Department of Chemistry, College of Science, King Saud University, Riyadh 11451 (Saudi Arabia)


    High-quality single crystalline Gallium Nitride (GaN) semiconductor has been synthesized using molecule beam epitaxy (MBE) technique for development of high-performance deep ultraviolet (UV) photodetectors. Thickness of the films was estimated by using surface profile meter and scanning electron microscope. Electronic states and elemental composition of the films were obtained using Raman scattering spectroscopy. The orientation, crystal structure and phase purity of the films were examined using a Siemens x-ray diffractometer radiation. The surface microstructure was studied using high resolution scanning electron microscopy (SEM). Two types of metal pairs: Al-Al, Al-Cu or Cu-Cu were used for interdigital electrodes on GaN film in order to examine the Schottky properties of the GaN based photodetector. The characterizations of the fabricated prototype include the stability, responsivity, response and recovery times. Typical time dependent photoresponsivity by switching different UV light source on and off five times for each 240 seconds at a bias of 2V, respectively, have been obtained. The detector appears to be highly sensitive to various UV wavelengths of light with very stable baseline and repeatability. The obtained photoresponsivity was up to 354 mA/W at the bias 2V. Higher photoresponsivity could be obtained if higher bias was applied but it would unavoidably result in a higher dark current. Thermal effect on the fabricated GaN based prototype was discussed.

  14. Fabrications and application of single crystalline GaN for high-performance deep UV photodetectors

    R. Velazquez


    Full Text Available High-quality single crystalline Gallium Nitride (GaN semiconductor has been synthesized using molecule beam epitaxy (MBE technique for development of high-performance deep ultraviolet (UV photodetectors. Thickness of the films was estimated by using surface profile meter and scanning electron microscope. Electronic states and elemental composition of the films were obtained using Raman scattering spectroscopy. The orientation, crystal structure and phase purity of the films were examined using a Siemens x-ray diffractometer radiation. The surface microstructure was studied using high resolution scanning electron microscopy (SEM. Two types of metal pairs: Al-Al, Al-Cu or Cu-Cu were used for interdigital electrodes on GaN film in order to examine the Schottky properties of the GaN based photodetector. The characterizations of the fabricated prototype include the stability, responsivity, response and recovery times. Typical time dependent photoresponsivity by switching different UV light source on and off five times for each 240 seconds at a bias of 2V, respectively, have been obtained. The detector appears to be highly sensitive to various UV wavelengths of light with very stable baseline and repeatability. The obtained photoresponsivity was up to 354 mA/W at the bias 2V. Higher photoresponsivity could be obtained if higher bias was applied but it would unavoidably result in a higher dark current. Thermal effect on the fabricated GaN based prototype was discussed.

  15. GaN nanostructure-based light emitting diodes and semiconductor lasers.

    Viswanath, Annamraju Kasi


    GaN and related materials have received a lot of attention because of their applications in a number of semiconductor devices such as LEDs, laser diodes, field effect transistors, photodetectors etc. An introduction to optical phenomena in semiconductors, light emission in p-n junctions, evolution of LED technology, bandgaps of various semiconductors that are suitable for the development of LEDs are discussed first. The detailed discussion on photoluminescence of GaN nanostructures is made, since this is crucial to develop optical devices. Fabrication technology of many nanostructures of GaN such as nanowires, nanorods, nanodots, nanoparticles, nanofilms and their luminescence properties are given. Then the optical processes including ultrafast phenomena, radiative, non-radiative recombination, quantum efficiency, lifetimes of excitons in InGaN quantum well are described. The LED structures based on InGaN that give various important colors of red, blue, green, and their design considerations to optimize the output were highlighted. The recent efforts in GaN technology are updated. Finally the present challenges and future directions in this field are also pointed out.

  16. Piezo-phototronic effect on electroluminescence properties of p-type GaN thin films.

    Hu, Youfan; Zhang, Yan; Lin, Long; Ding, Yong; Zhu, Guang; Wang, Zhong Lin


    We present that the electroluminescence (EL) properties of Mg-doped p-type GaN thin films can be tuned by the piezo-phototronic effect via adjusting the minority carrier injection efficiency at the metal-semiconductor (M-S) interface by strain induced polarization charges. The device is a metal-semiconductor-metal structure of indium tin oxide (ITO)-GaN-ITO. Under different straining conditions, the changing trend of the transport properties of GaN films can be divided into two types, corresponding to the different c-axis orientations of the films. An extreme value was observed for the integral EL intensity under certain applied strain due to the adjusted minority carrier injection efficiency by piezoelectric charges introduced at the M-S interface. The external quantum efficiency of the blue EL at 430 nm was changed by 5.84% under different straining conditions, which is 1 order of magnitude larger than the change of the green peak at 540 nm. The results indicate that the piezo-phototronic effect has a larger impact on the shallow acceptor states related EL process than on the one related to the deep acceptor states in p-type GaN films. This study has great significance on the practical applications of GaN in optoelectronic devices under a working environment where mechanical deformation is unavoidable such as for flexible/printable light emitting diodes.

  17. Dopant Effects on Defects in GaN Films Grown by Metal-Organic Chemical Vapour Deposition

    陆敏; 杨华; 黎子兰; 杨志坚; 李忠辉; 任谦; 金春来; 陆曙; 章蓓; 张国义


    The effects of dopants on the defects of GaN films were investigated by using different methods, such as wet,etching of pits, x-ray diffraction and photoluminescence (PL). Three kinds of the samples were prepared with different dopants, that is, nominally undoped, Si-doped and Mg-doped GaN films. It was found that the lowest density of the, etched pit was existed in the nominally undoped GaN, while the highest in the Mg-doped sample.The effects of the dopants on the, etching pits were discussed.

  18. Chemistry and electrical properties of surfaces of GaN and GaN/AlGaN heterostructures

    Hashizume, Tamotsu; Ootomo, Shinya; Oyama, Susumu; Konishi, Masanobu; Hasegawa, Hideki


    Chemical and electrical properties of the surfaces of GaN and GaN/AlGaN heterostructures were systematically investigated by x-ray photoelectron spectroscopy (XPS), capacitance–voltage, and current–voltage measurements. From in situ XPS study, relatively smaller band bending of 0.6 eV was seen at the GaN (2×2) surface grown by radio frequency-assisted molecular beam epitaxy on the metalorganic vapor phase epitaxy GaN template. After exposing the sample surface to air, strong band bending took...

  19. Fabrication of GaN Nanorods in a Large Scale on Si(111) Substrate by Ammoniating Technique

    AI Yu-Jie; XUE Cheng-Shan; SUN Li-Li; SUN Chuan-Wei; ZHUANG Hui-Zhao; WANG Fu-Xue; CHEN Jin-Hua; LI Hong


    @@ GaN nanorods in a large scale have been synthesized on Si (111) substrates by ammoniating Ga2Os/Mg films under flowing ammonia atmosphere at the temperature of 1000℃ for 15 min. The as-synthesized GaN nanorods are characterized by scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and highresolution transmission electron microscopy. The results demonstrate that these straight nanorods are hexagonal wurtzite GaN single crystals in diameters ranging from 200 nm to 600 nm.

  20. Utilisation of GaN and InGaN/GaN with nanoporous structures for water splitting

    Benton, J.; Bai, J.; Wang, T., E-mail: [Department of Electronic and Electrical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD (United Kingdom)


    We report a cost-effective approach to the fabrication of GaN based nanoporous structure for applications in renewable hydrogen production. Photoelectrochemical etching in a KOH solution has been employed to fabricate both GaN and InGaN/GaN nanoporous structures with pore sizes ranging from 25 to 60 nm, obtained by controlling both etchant concentration and applied voltage. Compared to as-grown planar devices the nanoporous structures have exhibited a significant increase of photocurrent with a factor of up to four times. An incident photon conversion efficiency of up to 46% around the band edge of GaN has been achieved.

  1. Ultra High p-doping Material Research for GaN Based Light Emitters

    Vladimir Dmitriev


    The main goal of the Project is to investigate doping mechanisms in p-type GaN and AlGaN and controllably fabricate ultra high doped p-GaN materials and epitaxial structures. Highly doped p-type GaN-based materials with low electrical resistivity and abrupt doping profiles are of great importance for efficient light emitters for solid state lighting (SSL) applications. Cost-effective hydride vapor phase epitaxial (HVPE) technology was proposed to investigate and develop p-GaN materials for SSL. High p-type doping is required to improve (i) carrier injection efficiency in light emitting p-n junctions that will result in increasing of light emitting efficiency, (ii) current spreading in light emitting structures that will improve external quantum efficiency, and (iii) parameters of Ohmic contacts to reduce operating voltage and tolerate higher forward currents needed for the high output power operation of light emitters. Highly doped p-type GaN layers and AlGaN/GaN heterostructures with low electrical resistivity will lead to novel device and contact metallization designs for high-power high efficiency GaN-based light emitters. Overall, highly doped p-GaN is a key element to develop light emitting devices for the DOE SSL program. The project was focused on material research for highly doped p-type GaN materials and device structures for applications in high performance light emitters for general illumination P-GaN and p-AlGaN layers and multi-layer structures were grown by HVPE and investigated in terms of surface morphology and structure, doping concentrations and profiles, optical, electrical, and structural properties. Tasks of the project were successfully accomplished. Highly doped GaN materials with p-type conductivity were fabricated. As-grown GaN layers had concentration N{sub a}-N{sub d} as high as 3 x 10{sup 19} cm{sup -3}. Mechanisms of doping were investigated and results of material studies were reported at several International conferences providing

  2. Slimmed May Day Holiday

    Liu Xinwen


    @@ Last November the State Council of China decided to renew its holiday system by reducing the seven-day Mav Dav holiday to three days and introducing three new one-day public holidays,namely the Qingming Festival,Dragon Boat Festival and Moon Festival.BY doing so,the three golden-week holidays that were introduced in 1999,namely the Spring Festival,Mav Dav and National Day,could be better distributed.The New Year's Eve holiday would remain one day.The new holiday plan was supposed to take effect in 2008.

  3. Deflection Reduction of GaN Wafer Bowing by Coating or Cutting Grooves in the Substrates

    SUN Tao; WANG Ming-Qing; SUN Yong-Jian; WANG Bo-Ping; ZHANG Guo-Yi; TONG Yu-Zhen; DUAN Hui-Ling


    @@ GaN films on sapphire substrates are obtained using the metal-organic chemical vapor deposition growth technique.We present two methods to reduce the GaN wafer bowing caused by the mismatch of the thermal expansion coefficients(TECs)between the film and the substrate.The first method is to use coating materials on the back side of the substrate whose TECs are smaller than that of the GaN films.The second is to cut grooves on the back side of the sapphire substrate and filling the grooves with appropriate materials(e.g., tungsten, silicon nitride).For each method, we minimize wafer bowing and even reduce it to zero.Moreover, the two methods can reduce stress concentration and suppress the propagation of cracks in the GaN/sapphire structure.%GaN films on sapphire substrates are obtained using the metal-organic chemical vapor deposition growth technique. We present two methods to reduce the GaN wafer bowing caused by the mismatch of the thermal expansion coefficients (TECs) between the film and the substrate. The first method is to use coating materials on the back side of the substrate whose TECs are smaller than that of the GaN films. The second is to cut grooves on the back side of the sapphire substrate and filling the grooves with appropriate materials (e.g., tungsten, silicon nitride).For each method, we minimize wafer bowing and even reduce it to zero. Moreover, the two methods can reduce stress concentration and suppress the propagation of cracks in the GaN/sapphire structure.

  4. A new system for sodium flux growth of bulk GaN. Part I: System development

    Von Dollen, Paul; Pimputkar, Siddha; Alreesh, Mohammed Abo; Albrithen, Hamad; Suihkonen, Sami; Nakamura, Shuji; Speck, James S.


    Though several methods exist to produce bulk crystals of gallium nitride (GaN), none have been commercialized on a large scale. The sodium flux method, which involves precipitation of GaN from a sodium-gallium melt supersaturated with nitrogen, offers potentially lower cost production due to relatively mild process conditions while maintaining high crystal quality. We successfully developed a novel apparatus for conducting crystal growth of bulk GaN using the sodium flux method which has advantages with respect to prior reports. A key task was to prevent sodium loss or migration from the growth environment while permitting N2 to access the growing crystal. We accomplished this by implementing a reflux condensing stem along with a reusable capsule containing a hermetic seal. The reflux condensing stem also enabled direct monitoring of the melt temperature, which has not been previously reported for the sodium flux method. Furthermore, we identified and utilized molybdenum and the molybdenum alloy TZM as a material capable of directly containing the corrosive sodium-gallium melt. This allowed implementation of a crucible-free system, which may improve process control and potentially lower crystal impurity levels. Nucleation and growth of parasitic GaN ("PolyGaN") on non-seed surfaces occurred in early designs. However, the addition of carbon in later designs suppressed PolyGaN formation and allowed growth of single crystal GaN. Growth rates for the (0001) Ga face (+c-plane) were up to 14 μm/h while X-ray omega rocking (ω-XRC) curve full width half-max values were 731″ for crystals grown using a later system design. Oxygen levels were high, >1019 atoms/cm3, possibly due to reactor cleaning and handling procedures.

  5. Effect of hydrogen on Ca and Mg acceptors in GaN

    Lee, J.W.; Pearton, S.J. [Univ. of Florida, Gainesville, FL (United States); Zolper, J.C. [Sandia National Labs., Albuquerque, NM (United States); Stall, R.A. [EMCORE Corp., Somerset, NJ (United States)


    The influence of minority carrier injection on the reactivation of hydrogen passivated Mg in GaN at 175 C has been investigated in p-n junction diodes. The dissociation of the neutral MgH complexes is greatly enhanced in the presence of minority carrier and the reactivation process follows second order kinetics. Conventional annealing under zero-bias conditions does not produce Mg-H dissociation until temperatures {ge} 450 C. These results provide an explanation for the e-beam induced reactivation of Mg acceptors in hydrogenated GaN. Exposure to a hydrogen plasma at 250 C of p-type GaN (Ca) prepared by either Ca{sup +} or Ca{sup +} plus P{sup +} coimplantation leads to a reduction in sheet carrier density of approximately an order of magnitude (1.6 {times} 10{sup 12} cm{sup {minus}2} to 1.8 {times} 10{sup 11} cm{sup {minus}2}), and an accompanying increase in hole mobility (6 cm{sup 2}/Vs to 18 cm{sup 2}/Vs). The passivation process can be reversed by post-hydrogenation annealing at 400--500 C under a N{sub 2} ambient. This reactivation of the acceptors is characteristic of the formation of neutral (Ca-H) complexes in the GaN. The thermal stability of the passivation is similar to that of Mg-H complexes in material prepared in the same manner (implantation) with similar initial doping levels. Hydrogen passivation of acceptor dopants in GaN appears to be a ubiquitous phenomenon, as it is in other p-type semiconductors.

  6. General Rushes Open Days Day II


    General Footage during the Open Days 2013 (Day 2 -29/09/2013) Images: Antoine Nouel, Clément Sbaffe, Victor Prunier, David Guerazzi, Basile Manent, Réemi Richarme, Noemi Caraban 00:00:00 00:08:56 Interviews 00:08:56 00:20:47 ALICE 00:20:47 00:26:52 ATLAS 00:26:52 00:28:07 Workshops 00:28:07 00:33:13 Crystal Lab 00:33:13 00:44:19 Superconductivity 00:44:19 01:04:42 Cryogenics 01:04:42 01:12:39 Transports 01:12:39 01:16:30 LEIR 01:16:30 01:18:28 LMF 01:18:28 01:19:50 Vacuum 01:19:50 01:36:39 Superconducting magnets (F1) 01:36:39 01:46:06 The idea filled world of vacuum (F2) 01:46:06 01:49:55 CCC 01:49:55 01:52:41 Safety Training Center 01:52:41 01:55:00 COMPASS 01:55:00 02:09:19 Robotics 02:09:19 02:18:36 LHC Point 6 (with DG) 02:18:36 02:25:16 LHC Point 4 02:25:16 02:29:29 LHCb 02:29:29 02:33:12 Control Center 02:33:12 02:39:57 Streets

  7. Open Day at SHMI.

    Jarosova, M.


    During the World Meteorological Day there has been preparing "Open Day" at Slovak Hydrometeorological Institute. This event has more than 10 years traditions. "Open Day" is one of a lot of possibilities to give more information about meteorology, climatology, hydrology too to public. This "Day" is executed in whole Slovakia. People can visit the laboratories, the forecasting room....and meteo and clima measuring points. The most popular is visiting forecasting room. Visitors are interested in e.g. climatologic change in Slovakia territory, preparing weather forecasting, dangerous phenomena.... Every year we have more than 500 visitors.

  8. InGaN light-emitting diodes with embedded nanoporous GaN distributed Bragg reflectors

    Shieh, Bing-Cheng; Jhang, Yuan-Chang; Huang, Kun-Pin; Huang, Wan-Chun; Dai, Jing-Jie; Lai, Chun-Feng; Lin, Chia-Feng


    InGaN-based light-emitting diodes (LEDs) with embedded conductive nanoporous GaN/undoped GaN (NP-GaN/u-GaN) distributed Bragg reflectors (DBRs) were demonstrated. Nanoporous GaN DBR structures were fabricated by pulsed 355 nm laser scribing and electrochemical etching processes. Heavily Si-doped n-type GaN:Si layers (n+-GaN) in an eight-period n+-GaN/u-GaN stack structure were transformed into a low-refractive-index, conductive nanoporous GaN structure. The measured center wavelength, peak reflectivity, and bandwidth of the nanoporous GaN DBR structure were 417 nm, 96.7%, and 34 nm, respectively. Resonance cavity modes of the photoluminescence spectra were observed in the treated LED structure with the nanoporous DBR structure.

  9. First-principles and thermodynamic analysis of trimethylgallium (TMG) decomposition during MOVPE growth of GaN

    Sekiguchi, K.; Shirakawa, H.; Yamamoto, Y.; Araidai, M.; Kangawa, Y.; Kakimoto, K.; Shiraishi, K.


    We analyzed the decomposition mechanisms of trimethylgallium (TMG) used for the gallium source of GaN fabrication based on first-principles calculations and thermodynamic analysis. We considered two conditions. One condition is under the total pressure of 1 atm and the other one is under metal organic vapor phase epitaxy (MOVPE) growth of GaN. Our calculated results show that H2 is indispensable for TMG decomposition under both conditions. In GaN MOVPE, TMG with H2 spontaneously decomposes into Ga(CH3) and Ga(CH3) decomposes into Ga atom gas when temperature is higher than 440 K. From these calculations, we confirmed that TMG surely becomes Ga atom gas near the GaN substrate surfaces.

  10. Etch Pits and Threading Dislocations in GaN Films Grown by Metal-Organic Chemical Vapor Deposition

    陆敏; 常昕; 黎子兰; 杨志坚; 张国义; 章蓓


    High quality epitaxial GaN films on (0001) sapphire substrates were grown by a commercial metal-organic chemical vapour deposition system. The, etch pits and threading dislocations in GaN films is studied by a scanning electron microscope (SEM) and a transmission-electron microscope (TEM). The SEM images of GaN films, etched in mixed acid solution (H3PO4:H2SO4 = 1: 3) and molten KOH exhibit notably different, etching pit densities of 5 × 108/cm2 and 4 × 107/cm2, respectively, which probably indicate that more kinds of, etching pits were revealed when, etched in mixed acid solution (H3PO4:H2SO4 = 1: 3). Cross section TEM of GaN films with different g vectors showed the portions of different threading dislocations. Theoretical calculation indicates that the lattice and thermal expansion coefficient mismatch may be the main origins of pure edge threading dislocations.

  11. Improved control over spontaneously formed GaN nanowires in molecular beam epitaxy using a two-step growth process.

    Zettler, J K; Corfdir, P; Geelhaar, L; Riechert, H; Brandt, O; Fernández-Garrido, S


    We investigate the influence of modified growth conditions during the spontaneous formation of GaN nanowires (NWs) on Si(111) in plasma-assisted molecular beam epitaxy. We find that a two-step growth approach, where the substrate temperature is increased during the nucleation stage, is an efficient method to gain control over the area coverage, average diameter, and coalescence degree of GaN NW ensembles. Furthermore, we also demonstrate that the growth conditions employed during the incubation time that precedes nanowire nucleation do not influence the properties of the final nanowire ensemble. Therefore, when growing GaN NWs at elevated temperatures or with low Ga/N ratios, the total growth time can be reduced significantly by using more favorable growth conditions for nanowire nucleation during the incubation time.

  12. Integrated Production of Ultra-Low Defect GaN Films and Devices for High-Power Amplifiers Project

    National Aeronautics and Space Administration — High quality GaN epitaxial films are key to current efforts for development of both high-power/high-speed electronic devices and optoelectronic devices. In fact,...

  13. Synthèse solvothermale de GaN et contribution à la cristallogenese de ce matériau

    Collado, Cécile


    Le nitrure de gallium, GaN, semi-conducteur à large gap (3.4 eV), est un composé qui présente des propriétés très attractives pour des applications en opto- et micro-électronique. L'amélioration des performances des dispositifs passe par l'amélioration des propriétés des films de GaN. C'est pourquoi l'obtention de monocristaux massifs de GaN, susceptibles de servir de substrats pour l'homoépitaxie de films de GaN, représente un enjeu considérable. L'objectif de ce travail de thèse était de tr...

  14. Effects of thickness on cubic GaN nucleation layers on GaAs(001) substrates

    X.H.Zheng; X.M.Jiang; 等


    The effects of growth time on the structure and morphology of cubic GaN nucleation layers on GaAs(001)substrates by metalorganic chemical vapor deposition (MOCVD) have been investigated using a synchrotron X-ray diffraction(XRD).The XRD results show that the GaN 111 reflections at 54.75° inχ are a measurable component,however the 002 reflections parallel to GaAs(001) surface are not detected.The XRD Φ scans and pole figures give a convincing proof that the GaN nucleation latyers show exactly the cubic symmetrical structure.The coherence lengths along the close-packed direction estuimated from the 111 peak are nanometer order of magnitude,The optimal photoluminescence (PL) spectrum was obtained from the cubic GaN epilayer deposited on the nucleation layer for 60sec.

  15. Comparative Analysis of Temperature-dependent .Raman Spectra of GaN and GaN/Mg Films

    WANG Rui-min; CHEN Guang-de; LIN J.-Y.,; JIANG H.-X.


    The Raman spectra of unintentionally doped gallium nitride (GaN) and Mg-doped GaN films were investigated and compared at room temperature and low temperature.The differences of E2 and AI(LO) mode in two samples are discussed.Stress relaxation is observed in Mg-doped GaN,and it is suggested that Mg-induced misfit dislocation and electron-phonon interaction are the possible origins.A peak at 247 cm-1 is observed in both the Raman spectra of GaN and Mg-doped GaN.Temperature-dependent Raman scattering experiment of Mgdoped GaN shows the frequency and intensity changes of this peak with temperature.This peak is attributed to the defect-induced vibrational mode.

  16. Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

    Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F.


    In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerence of GaAs and that Ti can protected GaAs from erosion by NH3. By depositing Ti on GaAs(111)A surface, a millor-like GaN layer could be grown at 1000 °C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future.

  17. GaN High-Electron-Mobility Transistor with WN x /Cu Gate for High-Power Applications

    Hsieh, Ting-En; Lin, Yueh-Chin; Li, Fang-Ming; Shi, Wang-Cheng; Huang, Yu-Xiang; Lan, Wei-Cheng; Chin, Ping-Chieh; Chang, Edward Yi


    A GaN high-electron-mobility transistor (HEMT) with WN x /Cu gate for high-power applications has been investigated. The direct-current (DC) characteristics of the device are comparable to those of conventional Ni/Au-gated GaN HEMTs. The results of high-voltage stress testing indicate that the device is stable after application of 200 V stress for 42 h. The WN x /Cu-gated GaN HEMT exhibited no obvious changes in the DC characteristics or Schottky barrier height before and after annealing at 250°C for 1 h. These results demonstrate that the WN x /Cu gate structure can be used in a GaN HEMT for high-power applications with good thermal stability.

  18. Integrated Production of Ultra-Low Defect GaN Films and Devices for High-Power Amplifiers Project

    National Aeronautics and Space Administration — High quality GaN epitaxial films are one of the keys to current efforts for development of both high-power/high-speed electronic devices and optoelectronic devices....

  19. Microstructures of GaN and In{sub x}Ga{sub 1-x}N films grown by MOCVD on free-standing GaN templates

    Jasinski, J.; Liliental-Weber, Z.; Huang, D.; Reshchikov, M.A.; Yun, F.; Morkoc, H.; Sone, C.; Park, S.S.; Lee, K.Y.


    We summarize structural properties of thick HVPE GaN templates from the point of view of their application as substrates for growth of nitride layers. This is followed by the results of optical and structural studies, mostly transmission electron microscopy, of nitride layers grown by MOCVD on top of the HVPE substrates. The results indicate high structural quality of these layers with a low density of threading dislocations (in the range of 10{sup 6} cm{sup -2}). Convergent beam electron diffraction studies showed that the MOCVD GaN films have Ga-polarity, the same polarity as the HVPE GaN substrates. Structural studies of an InGaN layer grown on top of the MOCVD GaN film showed the presence of two layers, which differed in lattice parameter and composition. The upper layer, on the top of the structure had a c-lattice parameter about 2% larger than that of GaN and contained 10.3 {+-} 0.8% of In. Values measured for the thinner, intermediate layer adjacent to the GaN layer were about 2 .5 times lower.

  20. XPS investigation of ion beam induced conversion of GaAs(0 0 1) surface into GaN overlayer

    Kumar, Praveen [Surface Physics and Nanostructure Group, National Physical Laboratory, New Delhi 110012 (India); Department of Physics, Indian Institute of Technology, New Delhi 110016 (India); Kumar, Mahesh; Govind [Surface Physics and Nanostructure Group, National Physical Laboratory, New Delhi 110012 (India); Mehta, B.R. [Department of Physics, Indian Institute of Technology, New Delhi 110016 (India); Shivaprasad, S.M., E-mail: [Jawaharlal Nehru Centre for Advanced Scientific Research, International Center for Material Science and Chemistry and Physics Materials Unit, Jakkur, 560064 Bangalore, Karnataka (India)


    For the advance of GaN based optoelectronic devices, one of the major barriers has been the high defect density in GaN thin films, due to lattice parameter and thermal expansion incompatibility with conventional substrates. Of late, efforts are focused in fine tuning epitaxial growth and in search for a low temperature method of forming low defect GaN with zincblende structure, by a method compatible to the molecular beam epitaxy process. In principle, to grow zincblende GaN the substrate should have four-fold symmetry and thus zincblende GaN has been prepared on several substrates including Si, 3C-SiC, GaP, MgO, and on GaAs(0 0 1). The iso-structure and a common shared element make the epitaxial growth of GaN on GaAs(0 0 1) feasible and useful. In this study ion-induced conversion of GaAs(0 0 1) surface into GaN at room temperature is optimized. At the outset a Ga-rich surface is formed by Ar{sup +} ion bombardment. Nitrogen ion bombardment of the Ga-rich GaAs surface is performed by using 2-4 keV energy and fluence ranging from 3 x 10{sup 13} ions/cm{sup 2} to 1 x 10{sup 18} ions/cm{sup 2}. Formation of surface GaN is manifested as chemical shift. In situ core level and true secondary electron emission spectra by X-ray photoelectron spectroscopy are monitored to observe the chemical and electronic property changes. Using XPS line shape analysis by deconvolution into chemical state, we report that 3 keV N{sub 2}{sup +} ions and 7.2 x 10{sup 17} ions/cm{sup 2} are the optimal energy and fluence, respectively, for the nitridation of GaAs(0 0 1) surface at room temperature. The measurement of electron emission of the interface shows the dependence of work function to the chemical composition of the interface. Depth profile study by using Ar{sup +} ion sputtering, shows that a stoichiometric GaN of 1 nm thickness forms on the surface. This, room temperature and molecular beam epitaxy compatible, method of forming GaN temperature can serve as an excellent template for

  1. General Rushes Open Days Day I


    General Footage during Open Days 2013 (Day 1 -28/09/2013) Images: Cameramen: Antoine Nouel, Clément Sbaffe, Victor Prunier, David Guerazzi, Basile Manent, Réemi Richarme, Noemi Caraban 00:00:00 00:03:40 Interviews 00:03:40 00:06:54 Beam Instrumentation 00:06:54 00:07:16 Globe 00:07:16 00:10:28 Microcosme 00:10:28 00:12:59 Lectures 00:12:59 00:27:52 Fun with physics 00:27:52 00:28:19 International Village 00:28:19 00:34:18 Fun Zone 00:34:18 00:47:50 ATLAS Surface 00:47:50 00:56:57 ATLAS underground 00:56:57 00:58:53 Detector technologies 00:58:53 01:04:39 CLIC 01:04:39 01:05:56 CMS surface 01:05:56 01:09:32 LINAC 2-3 01:09:32 01:15:29 LINAC 4 01:15:29 01:20:41 Computer Center 01:20:41 01:25:53 Clubs 01:25:53 01:31:49 Beam Instrumentation 01:31:49 01:35:27 Music Festival 01:35:27 01:37:31 SPS 01:37:31 01:46:13 CCC 01:46:13 01:48:24 Safety Trainig Center 01:48:24 01:52:38 COMPASS 01:52:38 01:56:09 EHN1 01:56:09 02:01:42 AMS 02:01:42 02:10:52 Robotics 02:10:52 02:22:48 LHC Point 4 02:22:48 02:23:48 Control Cent...

  2. The use of SiC/Si(111) hybrid substrate for MBE growth of GaN nanowires

    Reznik, R. R.; Kotlyar, K. P.; Ilkiv, I. V.; Soshnikov, I. P.; Kukushkin, S. A.; Osipov, A. V.; Nikitina, E. V.; Cirlin, G. E.


    This work demonstrates the possibility of using a silicon substrate with nanoscale buffer layer of silicon carbide for growth of GaN nanowires by molecular epitaxy on. Morphological and optical properties of the grown arrays are studied. It is shown that the integral intensity of the photoluminescence of such structures is more than 2 times higher than the best NWs GaN structures without buffer layer of silicon carbide.

  3. Structure and Properties of Semiconductor Microclusters GanPn(n=1-4):A First Principle Study

    ZHANG Cai-rong; CHEN Hong-shan; WANG Guang-hou


    The possible geometrical structures and relative stabilities of semiconductor microclusters GanPn(n= 1-4) were studied by virtue of density functional calculations with generalized gradient approximation (B3LYP).For the most stable isomers of GanPn(n= 1-4) clusters, the electronic structure, vibrational properties,dipole moment, polarizability and ionization potential were analyzed by means of HF, MP2, CISD and B3LYP methods with different basis sets.

  4. Growth and characterizations of GaN micro-rods on graphene films for flexible light emitting diodes

    Kunook Chung


    Full Text Available We report the growth of GaN micro-rods and coaxial quantum-well heterostructures on graphene films, together with structural and optical characterization, for applications in flexible optical devices. Graphene films were grown on Cu foil by means of chemical vapor deposition, and used as the substrates for the growth of the GaN micro-rods, which were subsequently transferred onto SiO2/Si substrates. Highly Si-doped, n-type GaN micro-rods were grown on the graphene films using metal–organic chemical vapor deposition. The growth and vertical alignment of the GaN micro-rods, which is a critical factor for the fabrication of high-performance light-emitting diodes (LEDs, were characterized using electron microscopy and X-ray diffraction. The GaN micro-rods exhibited promising photoluminescence characteristics for optoelectronic device applications, including room-temperature stimulated emission. To fabricate flexible LEDs, InxGa1–xN/GaN multiple quantum wells and a p-type GaN layer were deposited coaxially on the GaN micro-rods, and transferred onto Ag-coated polymer substrates using lift-off. Ti/Au and Ni/Au metal layers were formed to provide electrical contacts to the n-type and p-type GaN regions, respectively. The micro-rod LEDs exhibited intense emission of visible light, even after transfer onto the flexible polymer substrate, and reliable operation was achieved following numerous cycles of mechanical deformation.

  5. Valentine's Day



    Valentine’s Day,which falls on February14,is one of the most popular festivals of western society and even the whole world.It is a day for lovers,a day when people present chocolates,cards and can-dies to their beloved(心爱的人).

  6. Science Challenge Day

    Siegel, Deborah


    Science fairs can be good motivators, but as extracurricular activities, they leave some students behind. However, by staging a Science Challenge Day at school, educators can involve all students in doing everything from choosing activities to judging projects. This article presents a model for running a successful Science Challenge Day. The…


    Medical Service


    The CERN Medical Service is joining in with the world no tobacco day, which takes place on 31 May 2002. We encourage you to take this opportunity to stop smoking for good. Nurses and Doctors will be present on that day to give out information on methods to stop smoking and to assist you in your efforts.

  8. A Perfect Day



    THERE are days where not a thing goes wrong. There's not a glitch. Everything you expect happens, and then more comes along, not because you ask, but because it just does. It's the way life is supposed to be when life is perfect. Memory is what names that day perfect and analyzes it in order to create another, just like it.

  9. Formation of distinctive structures of GaN by inductively-coupled-plasma and reactive ion etching under optimized chemical etching conditions

    N. Okada


    Full Text Available We focused on inductively coupled plasma and reactive ion etching (ICP–RIE for etching GaN and tried to fabricate distinctive GaN structures under optimized chemical etching conditions. To determine the optimum chemical etching conditions, the flow rates of Ar and Cl2, ICP power, and chamber pressure were varied in the etching of c-plane GaN layers with stripe patterns. It was determined that the combination of Ar and Cl2 flow rates of 100 sccm, chamber pressure of 7 Pa, and ICP power of 800 W resulted in the most enhanced reaction, yielding distinctive GaN structures such as pillars with inverted mesa structures for c-plane GaN and a semipolar GaN layer with asymmetric inclined sidewalls. The selectivity and etching rate were also investigated.

  10. Formation of distinctive structures of GaN by inductively-coupled-plasma and reactive ion etching under optimized chemical etching conditions

    Okada, N.; Nojima, K.; Ishibashi, N.; Nagatoshi, K.; Itagaki, N.; Inomoto, R.; Motoyama, S.; Kobayashi, T.; Tadatomo, K.


    We focused on inductively coupled plasma and reactive ion etching (ICP-RIE) for etching GaN and tried to fabricate distinctive GaN structures under optimized chemical etching conditions. To determine the optimum chemical etching conditions, the flow rates of Ar and Cl2, ICP power, and chamber pressure were varied in the etching of c-plane GaN layers with stripe patterns. It was determined that the combination of Ar and Cl2 flow rates of 100 sccm, chamber pressure of 7 Pa, and ICP power of 800 W resulted in the most enhanced reaction, yielding distinctive GaN structures such as pillars with inverted mesa structures for c-plane GaN and a semipolar GaN layer with asymmetric inclined sidewalls. The selectivity and etching rate were also investigated.

  11. The influence of AlN/GaN superlattice intermediate layer on the properties of GaN grown on Si(111) substrates

    Liu Zhe; Wang Xiao-Liang; Wang Jun-Xi; Hu Guo-Xin; Guo Lun-Chun; Li Jin-Min


    AIN/GaN superlattice buffer is inserted between GaN epitaxial layer and Si substrate before epitaxial growth of GaN layer. High-quality and crack-free GaN epitaxial layers can be obtained by inserting AIN/GaN superlattice buffer layer. The influence of AIN/GaN superlattice buffer layer on the properties of GaN films are investigated in this paper. One of the important roles of the superlattice is to release tensile strain between Si substrate and epilayer. Raman spectra show a substantial decrease of in-plane tensile strain in GaN layers by vising AIN/GaN superlattice buffer layer. Moreover, TEM cross-sectional images show that the densities of both screw and edge dislocations are significantly reduced. The GaN films grown on Si with the superlattice buffer also have better surface morphology and optical properties.

  12. Optoelectronic Properties and Structural Characterization of GaN Thick Films on Different Substrates through Pulsed Laser Deposition

    Wei-Kai Wang


    Full Text Available Approximately 4-μm-thick GaN epitaxial films were directly grown onto a GaN/sapphire template, sapphire, Si(111, and Si(100 substrates by high-temperature pulsed laser deposition (PLD. The influence of the substrate type on the crystalline quality, surface morphology, microstructure, and stress states was investigated by X-ray diffraction (XRD, photoluminescence (PL, atomic force microscopy (AFM, transmission electron microscopy (TEM, and Raman spectroscopy. Raman scattering spectral analysis showed a compressive film stress of −0.468 GPa for the GaN/sapphire template, whereas the GaN films on sapphire, Si(111, and Si(100 exhibited a tensile stress of 0.21, 0.177, and 0.081 GPa, respectively. Comparative analysis indicated the growth of very close to stress-free GaN on the Si(100 substrate due to the highly directional energetic precursor migration on the substrate’s surface and the release of stress in the nucleation of GaN films during growth by the high-temperature (1000 °C operation of PLD. Moreover, TEM images revealed that no significant GaN meltback (Ga–Si etching process was found in the GaN/Si sample surface. These results indicate that PLD has great potential for developing stress-free GaN templates on different substrates and using them for further application in optoelectronic devices.

  13. Effect of growth temperature on defects in epitaxial GaN film grown by plasma assisted molecular beam epitaxy

    S. S. Kushvaha


    Full Text Available We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001 substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 108 cm−2 at 750 °C than that of the low temperature grown sample (1.1 × 109 cm−2 at 730 °C. A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.

  14. Effect of growth temperature on defects in epitaxial GaN film grown by plasma assisted molecular beam epitaxy

    Kushvaha, S. S., E-mail:; Pal, P.; Shukla, A. K.; Joshi, Amish G.; Gupta, Govind; Kumar, M.; Singh, S.; Gupta, Bipin K.; Haranath, D. [CSIR- National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi, India 110012 (India)


    We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001) substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 10{sup 8} cm{sup −2} at 750 °C) than that of the low temperature grown sample (1.1 × 10{sup 9} cm{sup −2} at 730 °C). A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.

  15. Nucleation phenomena during molecular beam epitaxy of GaN observed by line-of-sight quadrupole mass spectrometry

    Koblmueller, G.; Averbeck, R.; Riechert, H. [Infineon Technologies AG, Corporate Research Photonics, Otto-Hahn-Ring 6, 81739 Munich (Germany); Pongratz, P. [Vienna University of Technology, Institute of Solid State Physics, Wiedner Hauptstrasse 8-10, 1040 Vienna (Austria)


    We investigate nucleation and growth phenomena during molecular beam epitaxy of GaN on sapphire, 6H-SiC and GaN templates using in situ line-of-sight quadrupole mass spectrometry. Moreover, this method allows the quantitative study of nucleation phenomena by monitoring desorption processes. Heteroepitaxial growth of GaN on sapphire and 6H-SiC faces a high energy barrier to nucleation giving rise to a substantial Ga desorption during the initial phase of nucleation. The amount of initial Ga desorption in heteroepitaxy is independent of the chosen substrate material and is as high as 8 {+-} 1.5 nm equivalent GaN thickness. Once critical-sized islands have nucleated they grow three-dimensional (3D) leading to a quadratic increase of the GaN coverage and finally to a steady growth rate after coalescence, as also determined by Rutherford backscattering and atomic force microscopy. In contrast, homoepitaxy on Ga- and N-face GaN templates is distinguished by immediate nucleation. (Abstract Copyright [2002], Wiley Periodicals, Inc.)

  16. Effect of thickness on the microstructure of GaN films on Al203 (0001) by laser molecular beam epitaxy

    Liu Ying-Ying; Zhu Jun; Luo Wen-Bo; Hao Lan-Zhong; Zhang Ying; Li Yan-Rong


    Heteroepitaxia1l GaN films are grown on sapphire (0001) substrates using laser molecular beam epitaxy.The growth processes are in-situ monitored by reflection high energy electron diffraction.It is revealed that the growth mode of GaN transformed from three-dimensional (3D) island mode to two-dimensional (2D) layer-by-layer mode with the increase of thickness.This paper investigates the interfacial strain relaxation of GaN films by analysing their diffraction patterns.Calculation shows that the strain is completely relaxed when the thickness reaches 15 nm.The surface morphology evolution indicates that island merging and reduction of the island-edge barrier provide an effective way to make GaN films follow a 2D layer-by-layer growth mode.The 110-nm GaN films with a 2D growth mode have smooth regular hexagonal shapes.The X-ray diffraction indicates that thickness has a significant effect on the crystallized quality of GaN thin films.

  17. Investigation of defects and surface polarity in GaN using hot wet etching together with microscopy and diffraction techniques

    Visconti, P.; Huang, D.; Reshchikov, M.A.; Yun, F.; Cingolani, R.; Smith, D.J.; Jasinski, J.; Swider, W.; Liliental-Weber, Z.; Morkoc, H.


    The availability of reliable and quick methods to determine defect density and polarity in GaN films is of great interest. We have used photo-electrochemical (PEC) and hot wet etching using H{sub 3}PO{sub 4} and molten KOH to estimate the defect density in GaN films grown by hydride vapor phase epitaxy (HVPE) and molecular beam epitaxy (MBE). Free-standing whiskers and hexagonal etch pits are formed by PEC and wet etching respectively. Using Atomic Force Microscopy (AFM), we found the whisker density to be similar to etch pit densities for samples etched under precise conditions. Additionally Transmission Electron Microscopy (TEM) observations confirmed dislocation densities obtained by etching which increased our confidence in the consistency of methods used. Hot wet etching was used also to investigate the polarity of GaN films together with Convergent Beam Electron Diffraction (CBED) and AFM imaging. We found that hot H{sub 3}PO{sub 4} etches N-polarity GaN films very quickly resulting in the complete removal or drastic change of surface morphology as revealed by AFM or optical microscopy. On the contrary, the acid attacks only defect sites in Ga-polarity films producing nanometer-scale pits but leaving the defect-free GaN intact and the morphology unchanged. Additionally, the polarity assignments were related to the as-grown morphology and to the growth conditions of the buffer layer and the subsequent GaN layer.

  18. Localized tip enhanced Raman spectroscopic study of impurity incorporated single GaN nanowire in the sub-diffraction limit

    Patsha, Avinash, E-mail:, E-mail:; Dhara, Sandip; Tyagi, A. K. [Surface and Nanoscience Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India)


    The localized effect of impurities in single GaN nanowires in the sub-diffraction limit is reported using the study of lattice vibrational modes in the evanescent field of Au nanoparticle assisted tip enhanced Raman spectroscopy (TERS). GaN nanowires with the O impurity and the Mg dopants were grown by the chemical vapor deposition technique in the catalyst assisted vapor-liquid-solid process. Symmetry allowed Raman modes of wurtzite GaN are observed for undoped and doped nanowires. Unusually very strong intensity of the non-zone center zone boundary mode is observed for the TERS studies of both the undoped and the Mg doped GaN single nanowires. Surface optical mode of A{sub 1} symmetry is also observed for both the undoped and the Mg doped GaN samples. A strong coupling of longitudinal optical (LO) phonons with free electrons, however, is reported only in the O rich single nanowires with the asymmetric A{sub 1}(LO) mode. Study of the local vibration mode shows the presence of Mg as dopant in the single GaN nanowires.

  19. GaN layers with different polarities prepared by radio frequency molecular beam epitaxy and characterized by Raman scattering

    Zhong Fei; Li Xin-Hua; Qiu Kai; Yin Zhi-Jun; Ji Chang-Jian; Cao Xian-Cun; Han Qi-Feng; Chen Jia-Rong; Wang Yu-Qi


    GaN layers with different polarities have been prepared by radio-frequency molecular beam epitaxy (RF-MBE) and characterized by Raman scattering. Polarity control are realized by controlling Al/N flux ratio during high temperature AlN buffer growth. The Raman results illustrate that the N-polarity GaN films have frequency shifts at A1(LO) mode because of their high carrier density; the forbidden A1 (TO) mode occurs for mixed-polarity GaN films due to the destroyed translation symmetry by inversion domain boundaries (IDBS); Raman spectra for Ga-polarity GaN films show that they have neither frequency shifts mode nor forbidden mode. These results indicate that Ga-polarity GaN films have a better quality, and they are in good agreement with the results obtained from the room temperature Hall mobility. The best values of Ga-polarity GaN films are 1042 cm2/Vs with a carrier density of 1.0×1017 cm-3.

  20. Synthesis, optical properties and residual strain effect of GaN nanowires generated via metal-assisted photochemical electroless etching

    Najar, Adel


    Herein, we report on the studies of GaN nanowires (GaN NWs) prepared via a metal-assisted photochemical electroless etching method with Pt as the catalyst. It has been found that etching time greatly influences the growth of GaN NWs. The density and the length of nanowires increased with longer etching time, and excellent substrate coverage was observed. The average nanowire width and length are around 35 nm and 10 μm, respectively. Transmission electron microscopy (TEM) shows a single-crystalline wurtzite structure and is confirmed by X-ray measurements. The synthesis mechanism of GaN NWs using the metal-assisted photochemical electroless etching method was presented. Photoluminescence (PL) measurements of GaN NWs show red-shift PL peaks compared to the as-grown sample associated with the relaxation of compressive stress. Furthermore, a shift of the E2 peak to the lower frequency in the Raman spectra for the samples etched for a longer time confirms such a stress relaxation. Based on Raman measurements, the compressive stress σxx and the residual strain εxx were evaluated to be 0.23 GPa and 2.6 × 10−4, respectively. GaN NW synthesis using a low cost method might be used for the fabrication of power optoelectronic devices and gas sensors.

  1. Clinical efficacy and tolerability of Gosha-jinki-gan, a Japanese traditional herbal medicine, for nocturia.

    Yagi, Hiroshi; Nishio, Kojiro; Sato, Ryo; Arai, Gaku; Soh, Shigehiro; Okada, Hiroshi


    We evaluated the efficacy and tolerability of Gosha-jinki-gan (GJG; jì shēng shèn qì wán) in 30 cases of nocturia ( yè niào) unresponsive to α1-blockers or antimuscarinic drugs. All patients received GJG extract powder (2.5 g) three times a day for 12 weeks as an add-on therapy to α1-blockers or antimuscarinic drugs. Subjective outcomes assessed by the International Prostate Symptom Score-quality of life, and the benign prostatic hyperplasia impact index and objective outcomes assessed by urinary frequency and the urine production rate at night showed significant improvement after treatment. Moreover, other objective outcomes assessed by maximum flow rates, postvoid residual, serum human atrial natriuretic peptide levels, and urinary 8-hydroxy-2'-deoxyguanosine levels did not change. Adverse events were observed in 10% of cases; however, these events were mild. GJG appears to be a safe and effective potential therapeutic alternative for patients with nocturia unresponsive to α1-blockers or antimuscarinic drugs. Further clinical investigations are required to elucidate the precise pathophysiologic mechanisms of GJG in nocturia.

  2. Materials physics and device development for improved efficiency of GaN HEMT high power amplifiers.

    Kurtz, Steven Ross; Follstaedt, David Martin; Wright, Alan Francis; Baca, Albert G.; Briggs, Ronald D.; Provencio, Paula Polyak; Missert, Nancy A.; Allerman, Andrew Alan; Marsh, Phil F.; Koleske, Daniel David; Lee, Stephen Roger; Shul, Randy John; Seager, Carleton Hoover; Tigges, Christopher P.


    GaN-based microwave power amplifiers have been identified as critical components in Sandia's next generation micro-Synthetic-Aperture-Radar (SAR) operating at X-band and Ku-band (10-18 GHz). To miniaturize SAR, GaN-based amplifiers are necessary to replace bulky traveling wave tubes. Specifically, for micro-SAR development, highly reliable GaN high electron mobility transistors (HEMTs), which have delivered a factor of 10 times improvement in power performance compared to GaAs, need to be developed. Despite the great promise of GaN HEMTs, problems associated with nitride materials growth currently limit gain, linearity, power-added-efficiency, reproducibility, and reliability. These material quality issues are primarily due to heteroepitaxial growth of GaN on lattice mismatched substrates. Because SiC provides the best lattice match and thermal conductivity, SiC is currently the substrate of choice for GaN-based microwave amplifiers. Obviously for GaN-based HEMTs to fully realize their tremendous promise, several challenges related to GaN heteroepitaxy on SiC must be solved. For this LDRD, we conducted a concerted effort to resolve materials issues through in-depth research on GaN/AlGaN growth on SiC. Repeatable growth processes were developed which enabled basic studies of these device layers as well as full fabrication of microwave amplifiers. Detailed studies of the GaN and AlGaN growth of SiC were conducted and techniques to measure the structural and electrical properties of the layers were developed. Problems that limit device performance were investigated, including electron traps, dislocations, the quality of semi-insulating GaN, the GaN/AlGaN interface roughness, and surface pinning of the AlGaN gate. Surface charge was reduced by developing silicon nitride passivation. Constant feedback between material properties, physical understanding, and device performance enabled rapid progress which eventually led to the successful fabrication of state of the

  3. A Numerical Technique for Removing Residual Gate-Source Capacitances When Extracting Parasitic Inductance for GaN High Electron Mobility Transistors (HEMTs)


    Residual Gate-source Capacitances When Extracting Parasitic Inductance for GaN High Electron Mobility Transistors ( HEMTs ) Benjamin Huebschman and Pankaj...Extracting Parasitic Inductance for GaN High Electron Mobility Transistors ( HEMTs ) 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6...nitride ( GaN ) high electron mobility transistors ( HEMTs ) begin to realize their performance potential, and to transition from experimental devices to

  4. 0.15-micron Gallium Nitride (GaN) Microwave Integrated Circuit Designs Submitted to TriQuint Semiconductor for Fabrication


    arsenide GaN gallium nitride LNA low-noise amplifier MMIC monolithic microwave integrated circuit PA power amplifier HEMT high electron mobility...0.15-µm Gallium Nitride ( GaN ) Microwave Integrated Circuit Designs Submitted to TriQuint Semiconductor for Fabrication by John Penn ARL...MD 20783-1197 ARL-TN-0496 September 2012 0.15-µm Gallium Nitride ( GaN ) Microwave Integrated Circuit Designs Submitted to TriQuint

  5. That Rainy Day



    Many things have happened since I began to remember things. Pleasant or sad, they've left some impressions on my mind. Some are fading from my memory while others are and will be remembered for ever as if they had happened yesterday, and the scene on that rainy day is just one of such memories. It was on July 7th, 1990, the first day of the 3-day college entrance examination. I got up early that morning, feeling so excited and nervous that I lost all my appetite. What's worse, it began raining, adding vexat...

  6. Probing temperature gradients within the GaN buffer layer of AlGaN/GaN high electron mobility transistors with Raman thermography

    Hodges, C., E-mail:; Pomeroy, J.; Kuball, M. [H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL (United Kingdom)


    We demonstrate the ability of confocal Raman thermography using a spatial filter and azimuthal polarization to probe vertical temperature gradients within the GaN buffer layer of operating AlGaN/GaN high electron mobility transistors. Temperature gradients in the GaN layer are measured by using offset focal planes to minimize the contribution from different regions of the GaN buffer. The measured temperature gradient is in good agreement with a thermal simulation treating the GaN thermal conductivity as homogeneous throughout the layer and including a low thermal conductivity nucleation layer to model the heat flow between the buffer and substrate.

  7. A new approach to epitaxially grow high-quality GaN films on Si substrates: the combination of MBE and PLD.

    Wang, Wenliang; Wang, Haiyan; Yang, Weijia; Zhu, Yunnong; Li, Guoqiang


    High-quality GaN epitaxial films have been grown on Si substrates with Al buffer layer by the combination of molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) technologies. MBE is used to grow Al buffer layer at first, and then PLD is deployed to grow GaN epitaxial films on the Al buffer layer. The surface morphology, crystalline quality, and interfacial property of as-grown GaN epitaxial films on Si substrates are studied systematically. The as-grown ~300 nm-thick GaN epitaxial films grown at 850 °C with ~30 nm-thick Al buffer layer on Si substrates show high crystalline quality with the full-width at half-maximum (FWHM) for GaN(0002) and GaN(102) X-ray rocking curves of 0.45° and 0.61°, respectively; very flat GaN surface with the root-mean-square surface roughness of 2.5 nm; as well as the sharp and abrupt GaN/AlGaN/Al/Si hetero-interfaces. Furthermore, the corresponding growth mechanism of GaN epitaxial films grown on Si substrates with Al buffer layer by the combination of MBE and PLD is hence studied in depth. This work provides a novel and simple approach for the epitaxial growth of high-quality GaN epitaxial films on Si substrates.

  8. Characterization and density control of GaN nanodots on Si (111) by droplet epitaxy using plasma-assisted molecular beam epitaxy.

    Yu, Ing-Song; Chang, Chun-Pu; Yang, Chung-Pei; Lin, Chun-Ting; Ma, Yuan-Ron; Chen, Chun-Chi


    In this report, self-organized GaN nanodots have been grown on Si (111) by droplet epitaxy method, and their density can be controlled from 1.1 × 10(10) to 1.1 × 10(11) cm(-2) by various growth parameters, such as substrate temperatures for Ga droplet formation, the pre-nitridation treatment of Si substrate, the nitridation duration for GaN crystallization, and in situ annealing after GaN formation. Based on the characterization of in situ RHEED, we can observe the surface condition of Si and the formation of GaN nanodots on Si. The surface nitridaiton treatment at 600°C provides a-SiNx layer which makes higher density of GaN nanodots. Crystal GaN nanodots can be observed by the HRTEM. The surface composition of GaN nanodots can be analyzed by SPEM and μ-XPS with a synchrotron x-ray source. We can find GaN nanodots form by droplet epitaxy and then in situ annealing make higher-degree nitridation of GaN nanodots.

  9. Influence of vicinal sapphire substrate on the properties of N-polar GaN films grown by metal-organic chemical vapor deposition

    Lin, Zhiyu; Zhang, Jincheng, E-mail:; Xu, Shengrui; Chen, Zhibin; Yang, Shuangyong; Tian, Kun; Hao, Yue [Key Lab of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi' an, Shaanxi 710071 (China); Su, Xujun [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou, Jiangsu 215123 (China); Shi, Xuefang [School of Advanced Materials and Nanotechnology, Xidian University, Xi' an, Shaanxi 710071 (China)


    The influence of vicinal sapphire substrates on the growth of N-polar GaN films by metal-organic chemical vapor deposition is investigated. Smooth GaN films without hexagonal surface feature are obtained on vicinal substrate. Transmission electron microscope results reveal that basal-plane stacking faults are formed in GaN on vicinal substrate, leading to a reduction in threading dislocation density. Furthermore, it has been found that there is a weaker yellow luminescence in GaN on vicinal substrate than that on (0001) substrate, which might be explained by the different trends of the carbon impurity incorporation.

  10. High kappa Dielectrics on InGaAs and GaN - Growth, Interfacial Structural Studies, and Surface Fermi Level Unpinning


    interface have attributed to the high device performance. In addition, compared to the state-of-the-art GaN HEMT devices, the HfO2/ GaN MOSFET...Final Report for FA2386-10-1-4058 AOARD Grant 104058 Research Title: High  dielectrics on InGaAs and GaN - Growth, interfacial structural studies...on the science and technology of III-V InGaAs and GaN metal-oxide-semiconductor (MOS) systems using high dielectrics. The new technology of high

  11. Characterization and density control of GaN nanodots on Si (111) by droplet epitaxy using plasma-assisted molecular beam epitaxy

    Yu, Ing-Song; Chang, Chun-Pu; Yang, Chung-Pei; Lin, Chun-Ting; Ma, Yuan-Ron; Chen, Chun-Chi


    In this report, self-organized GaN nanodots have been grown on Si (111) by droplet epitaxy method, and their density can be controlled from 1.1 × 1010 to 1.1 × 1011 cm-2 by various growth parameters, such as substrate temperatures for Ga droplet formation, the pre-nitridation treatment of Si substrate, the nitridation duration for GaN crystallization, and in situ annealing after GaN formation. Based on the characterization of in situ RHEED, we can observe the surface condition of Si and the formation of GaN nanodots on Si. The surface nitridaiton treatment at 600°C provides a-SiNx layer which makes higher density of GaN nanodots. Crystal GaN nanodots can be observed by the HRTEM. The surface composition of GaN nanodots can be analyzed by SPEM and μ-XPS with a synchrotron x-ray source. We can find GaN nanodots form by droplet epitaxy and then in situ annealing make higher-degree nitridation of GaN nanodots.

  12. Days of Rock



    FROM last October 1 st to 3rd, at the foot of Fragrant Hill, a suburban Beijing resort famous for its flaming maple leaves in autumn, more than 20,000 rock fans indulged themselves in music for three days.

  13. My Happiest Day

    姚晶晶; 万正芬


    Yesterday I was fourteen years old. Of course, it was my birlhday. My parents were both at home, I wanted to have o birthday party, so they helped me get everything ready for the biilhday the day before yesterday.

  14. Adult Day Services

    ... the National Adult Day Services Association. 2. U.S. Health Care Costs: Background Brief , The Henry J. Kaiser Family Foundation (2008) (; excerpt from Nursing Homes and Assisted Living Industry Profile , First Research ( ...

  15. Open Day: General Information

    2004-01-01 With 50 visit points, including theatre performances, debates and visits to installations that have never before been opened to the public, CERN's 50th anniversary Open Day is set to be a day to remember. Seven hundred volunteers have signed up to help for the day. The Open Day team truly appreciates this wonderful show of support! The Open Day would not be possible without their help. Car parking and Access Cars with a CERN sticker can access all CERN sites as normal. However, to avoid congestion on Meyrin site, we ask you to park in areas that will not be open to the public (see below) and to use the shuttle services wherever possible for your transport during the day. Private cars on the French side of the border without a CERN sticker will be diverted to a car park area in the Prévessin site. There is a shuttle service connecting the Meyrin and Prévessin sites via SM18 every 20 minutes. Private cars on the Swiss side of the border without a CERN sticker will be diverte...

  16. Sun-Earth Days

    Thieman, J.; Ng, C.; Lewis, E.; Cline, T.


    Sun-Earth Day is a well-coordinated series of programs, resources and events under a unique yearly theme highlighting the fundamentals of heliophysics research and missions. A menu of activities, conducted throughout the year, inspire and educate participants. Sun-Earth Day itself can vary in date, but usually is identified by a celebration on or near the spring equinox. Through the Sun-Earth Day framework we have been able to offer a series of coordinated events that promote and highlight the Sun, its connection to Earth and the other planets. Sun-Earth Day events are hosted by educators, museums, amateur astronomers and scientists and occur at schools, community groups, parks, planetaria and science centers around the globe. Sun-Earth Day raises the awareness and knowledge of formal and informal education audiences concerning space weather and heliophysics. By building on the success of Sun-Earth Day yearly celebrations, we seek to affect people of all backgrounds and ages with the wonders of heliophysics science, discovery, and exploration in ways that are both tangible and meaningful to their lives.

  17. An extended day program

    Ševkušić-Mandić Slavica G.


    Full Text Available The paper presents the results of a pilot project evaluation, carried out as an action investigation whose aim was to provide a better quality extended day for primary school students. The project included the training of teachers involved in extended day program, designing of special activities performed by teachers with children once a week as well as changes and equipping of premises where children stay. The aims of the program were conception and performance of activities in a less formal way than during regular instructional days, linking of learning at school and acquired knowledge to everyday experiences, and work on contents contributing to the development of child's interests and creativity. The program was accomplished in a Belgrade primary school during the 2001/2002 academic year, comprising students of 1st and 2nd grades (N=77. The effects of the program were monitored throughout the academic year (observation and teachers' reports on accomplished workshops and at the end of the academic year (teachers and students' opinions of the program, academic achievement and creativity of students attending the extended day program compared with students not attending it. Findings about positive effects of the program on students' broadening of interests and willingness to express themselves creatively, indicate unequivocally that there is a need for developing special extended day programs. The extended day program is an opportunity for school to exert greater educational influence that has yet to be tapped.

  18. Multilayer porous structures of HVPE and MOCVD grown GaN for photonic applications

    Braniste, T.; Ciers, Joachim; Monaico, Ed.; Martin, D.; Carlin, J.-F.; Ursaki, V. V.; Sergentu, V. V.; Tiginyanu, I. M.; Grandjean, N.


    In this paper we report on a comparative study of electrochemical processes for the preparation of multilayer porous structures in hydride vapor phase epitaxy (HVPE) and metal organic chemical vapor phase deposition (MOCVD) grown GaN. It was found that in HVPE-grown GaN, multilayer porous structures are obtained due to self-organization processes leading to a fine modulation of doping during the crystal growth. However, these processes are not totally under control. Multilayer porous structures with a controlled design have been produced by optimizing the technological process of electrochemical etching in MOCVD-grown samples, consisting of five pairs of thin layers with alternating-doping profiles. The samples have been characterized by SEM imaging, photoluminescence spectroscopy, and micro-reflectivity measurements, accompanied by transfer matrix analysis and simulations by a method developed for the calculation of optical reflection spectra. We demonstrate the applicability of the produced structures for the design of Bragg reflectors.

  19. Ferromagnetism in GaN and SiC doped with transition metals

    Pearton, S.J.; Park, Y.D.; Abernathy, C.R.; Overberg, M.E.; Thaler, G.T.; Kim, J.; Ren, F.; Zavada, J.M.; Wilson, R.G


    Recent results on achieving ferromagnetism in transition metal-doped GaN, SiC and related materials are discussed. While current generations of semiconductor electronic and photonic devices utilize the charge on electrons and holes in order to perform their specific functionality such as signal processing or light emission, the field of semiconductor spintronics seeks to exploit the spin of charge carriers in new generations of transistors, lasers and integrated magnetic sensors. There is strong potential for new classes of ultra-low power, high-speed memory, logic and photonic devices. The utility of such devices depends on the availability of materials with practical magnetic ordering temperatures and most theories predict that the Curie temperature will be a strong function of bandgap. Here we review the field of wide bandgap dilute magnetic semiconductors, such as GaN, SiC and related materials, exhibiting room temperature ferromagnetism, the origins of the magnetism and its potential applications.

  20. Direct experimental determination of the spontaneous polarization of GaN

    Lähnemann, Jonas; Brandt, Oliver; Jahn, Uwe; Pfüller, Carsten; Roder, Claudia; Dogan, Pinar; Grosse, Frank; Belabbes, Abderrezak; Bechstedt, Friedhelm; Trampert, Achim; Geelhaar, Lutz


    We present a universal approach for determining the spontaneous polarization Psp of a wurtzite semiconductor from the emission energies of excitons bound to the different types of stacking faults in these crystals. Employing microphotoluminescence and cathodoluminescence spectroscopy, we observe emission lines from the intrinsic and extrinsic stacking faults in strain-free GaN microcrystals. By treating the polarization sheet charges associated with these stacking faults as a plate capacitor, Psp can be obtained from the observed transition energies with no additional assumptions. Self-consistent Poisson-Schrödinger calculations, aided by the microscopic electrostatic potential computed using density-functional theory, lead to nearly identical values for Psp. Our recommended value for Psp of GaN is -0.022±0.007 C/m2.

  1. Phonon deformation potentials of hexagonal GaN studied by biaxial stress modulation

    Jun-Yong Lu


    Full Text Available In this work, a biaxial stress modulation method, combining the microfabrication technique, finite element analysis and a weighted averaging process, was developed to study piezospectroscopic behavior of hexagonal GaN films, epitaxially grown by metalorganic chemical vapor deposition on c-sapphire and Si (111 substrates. Adjusting the size of patterned islands, various biaxial stress states could be obtained at the island centers, leading to abundant stress-Raman shift data. With the proposed stress modulation method, the Raman biaxial stress coefficients of E2H and A1 (LO phonons of GaN were determined to be 3.43 cm-1/GPa and 2.34 cm-1/GPa, respectively.

  2. Polarization of stacking fault related luminescence in GaN nanorods

    G. Pozina


    Full Text Available Linear polarization properties of light emission are presented for GaN nanorods (NRs grown along [0001] direction on Si(111 substrates by direct-current magnetron sputter epitaxy. The near band gap photoluminescence (PL measured at low temperature for a single NR demonstrated an excitonic line at ∼3.48 eV and the stacking faults (SFs related transition at ∼3.43 eV. The SF related emission is linear polarized in direction perpendicular to the NR growth axis in contrast to a non-polarized excitonic PL. The results are explained in the frame of the model describing basal plane SFs as polymorphic heterostructure of type II, where anisotropy of chemical bonds at the interfaces between zinc blende and wurtzite GaN subjected to in-built electric field is responsible for linear polarization parallel to the interface planes.

  3. An improved temperature-dependent large signal model of microwave GaN HEMTs

    Changsi, Wang; Yuehang, Xu; Zhang, Wen; Zhikai, Chen; Ruimin, Xu


    Accurate modeling of the electrothermal effects of GaN electronic devices is critical for reliability design and assessment. In this paper, an improved temperature-dependent model for large signal equivalent circuit modeling of GaN HEMTs is proposed. To accurately describe the thermal effects, a modified nonlinear thermal sub-circuit which is related not only to power dissipation, but also ambient temperature is used to calculate the variations of channel temperature of the device; the temperature-dependent parasitic and intrinsic elements are also taken into account in this model. The parameters of the thermal sub-circuit are extracted by using the numerical finite element method. The results show that better performance can be achieved by using the proposed large signal model in the range of -55 to 125 °C compared with the conventional model with a linear thermal sub-circuit. Project supported by the National Natural Science Foundation of China (No. 61106115).

  4. Evidence of satellite valley position in GaN by photoexcited field emission spectroscopy

    Yilmazoglu, O.; Pavlidis, D.; Hartnagel, H. L.; Evtukh, A.; Litovchenko, V.; Semenenko, N.


    GaN field emitter rods with nanometer diameter were fabricated by photoelectrochemical etching on a n+-GaN substrate. Their electron field emission properties were investigated under ultraviolet (UV) illumination. The Fowler-Nordheim plots of the emission current show different slopes for nonilluminated and UV illuminated devices. A model based on the electron emission from valleys having different specific electron affinities is proposed to explain the experimental results. In the absence of illumination, the GaN rods are almost fully depleted and emission takes place only from the lower valley. Upon UV illumination and presence of a high electric field at the emitter tip, the upper valley of the conduction band appears to be occupied by electrons generated at the valence band. The energy difference between the lower and upper valleys was determined to be 1.15eV and is in good agreement with formerly published theoretical and measured values.

  5. Unidirectional expansion of lattice parameters in GaN induced by ion implantation

    Fa Tao; Li Lin; Yao Shu-De; Wu Ming-Fang; Zhou Sheng-Qiang


    This paper reports that the 150-keV Mn ions are implanted into GaN thin film grown on Al2O3 by metalorganic chemical vapour deposition. The X-ray diffraction reciprocal spacing mapping is applied to study the lattice parameter variation upon implantation and post-annealing. After implantation, a significant expansion is observed in the perpendicular direction. The lattice strain in perpendicular direction strongly depends on ion fluence and implantation geometry and can be partially relaxed by post-annealing. While in the parallel direction, the lattice parameter approximately keeps the same as the unimplanted GaN, which is independent of ion fluence, implantation geometry and post-annealing temperature.

  6. (-201) β-Gallium oxide substrate for high quality GaN materials

    Roqan, Iman S.


    (-201) oriented β-Ga2O3 has the potential to be used as a transparent and conductive substrate for GaN-growth. The key advantages of Ga2O3 are its small lattice mismatches (4.7%), appropriate structural, thermal and electrical properties and a competitive price compared to other substrates. Optical characterization show that GaN layers grown on (-201) oriented β-Ga2O3 are dominated by intense bandedge emission with a high luminescence efficiency. Atomic force microscopy studies show a modest threading dislocation density of ~108 cm-2, while complementary Raman spectroscopy indicates that the GaN epilayer is of high quality with slight compressive strain. Room temperature time-findings suggest that the limitation of the photoluminescence lifetime (~500 ps) is due to nonradiative recombination arising from threading dislocation. Therefore, by optimizing the growth conditions, high quality material with significant optical efficiency can be obtained.

  7. Photoelectrochemical liftoff of LEDs grown on freestanding c-plane GaN substrates.

    Hwang, David; Yonkee, Benjamin P; Addin, Burhan Saif; Farrell, Robert M; Nakamura, Shuji; Speck, James S; DenBaars, Steven


    We demonstrate a thin-film flip-chip (TFFC) process for LEDs grown on freestanding c-plane GaN substrates. LEDs are transferred from a bulk GaN substrate to a sapphire submount via a photoelectrochemical (PEC) undercut etch. This PEC liftoff method allows for substrate reuse and exposes the N-face of the LEDs for additional roughening. The LEDs emitted at a wavelength of 432 nm with a turn on voltage of ~3 V. Etching the LEDs in heated KOH after transferring them to a sapphire submount increased the peak external quantum efficiency (EQE) by 42.5% from 9.9% (unintentionally roughened) to 14.1% (intentionally roughened).

  8. Surface States Effect on the Large Photoluminescence Redshift in GaN Nanostructures

    Ben Slimane, Ahmed


    We report on the large photoluminescence redshift observed in nanostructures fabricated using n-type GaN by ultraviolet (UV) metal-assisted electroless chemical-etching method. The scanning electron microscopy (SEM) characterization showed nanostructures with size dispersion ranging from 10 to 100 nm. We observed the crystalline structure using high resolution transmission electron microscopy (HRTEM) and electron energy loss (EELS) techniques. In contrast to 362 nm UV emission from the GaN epitaxy, the nanostructures emitted violet visible-light in photoluminescence (PL) characterization with increasing optical excitation. An energy band model was presented to shed light on the large PL redshift under the influence of surface states, which resulted in two competing photoluminescence mechanisms depending on excitation conditions.

  9. Photoelectrochemical liftoff of LEDs grown on freestanding c-plane GaN substrates

    Hwang, David


    We demonstrate a thin-film flip-chip (TFFC) process for LEDs grown on freestanding c-plane GaN substrates. LEDs are transferred from a bulk GaN substrate to a sapphire submount via a photoelectrochemical (PEC) undercut etch. This PEC liftoff method allows for substrate reuse and exposes the N-face of the LEDs for additional roughening. The LEDs emitted at a wavelength of 432 nm with a turn on voltage of ~3 V. Etching the LEDs in heated KOH after transferring them to a sapphire submount increased the peak external quantum efficiency (EQE) by 42.5% from 9.9% (unintentionally roughened) to 14.1% (intentionally roughened).

  10. Growth and magnetization study of transition metal doped GaN nanostructures

    Gupta, Shalini; Kang, Hun; Park, Eun-Hyun [Georgia Institute of Technology, School of Electrical and Computer Engineering, Atlanta, GA (United States); Kane, Matthew H.; Ferguson, Ian T. [Georgia Institute of Technology, School of Electrical and Computer Engineering, Atlanta, GA (United States); Georgia Institute of Technology, School of Materials Science and Engineering, Atlanta, GA (United States)


    This work presents the MOCVD growth and characterization of optically active GaN nanostructures which have been doped with the transition metals manganese and iron for potential spintronic applications. Introduction of both these transition metals in GaN nanostructures enhanced the nucleation of the nanostructures resulting in reduced lateral dimensions and increased nanostructure density. Both Ga{sub 1-x}Mn{sub x}N and Ga{sub 1-x}Fe{sub x}N nanostructures showed hysteresis behaviour at 5 K. Further VSM measurements on Ga{sub 1-x}Fe{sub x}N nanostructures at 300 K showed a hysteresis curve with a reduced coercive filed and displayed superparamagnetic behaviour. These magnetically active nanostructures are promising and provide an incentive to further study them with the aim of eventually utilizing them in spintronic applications and improving device efficiency. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Influence of oxygen in architecting large scale nonpolar GaN nanowires

    Patsha, Avinash; Pandian, Ramanathaswamy; Dhara, S


    Manipulation of surface architecture of semiconducting nanowires with a control in surface polarity is one of the important objectives for nanowire based electronic and optoelectronic devices for commercialization. We report the growth of exceptionally high structural and optical quality nonpolar GaN nanowires with controlled and uniform surface morphology and size distribution, for large scale production. The role of O contamination (~1-10^5 ppm) in the surface architecture of these nanowires is investigated with the possible mechanism involved. Nonpolar GaN nanowires grown in O rich condition show the inhomogeneous surface morphologies and sizes (50 - 150 nm) while nanowires are having precise sizes of 40(5) nm and uniform surface morphology, for the samples grown in O reduced condition. Relative O contents are estimated using electron energy loss spectroscopy studies. Size-selective growth of uniform nanowires is also demonstrated, in the O reduced condition, using different catalyst sizes. Photoluminescen...

  12. Photoluminescence quantum efficiency of Er optical centers in GaN epilayers.

    Ho, V X; Dao, T V; Jiang, H X; Lin, J Y; Zavada, J M; McGill, S A; Vinh, N Q


    We report the quantum efficiency of photoluminescence processes of Er optical centers as well as the thermal quenching mechanism in GaN epilayers prepared by metal-organic chemical vapor deposition. High resolution infrared spectroscopy and temperature dependence measurements of photoluminescence intensity from Er ions in GaN under resonant excitation excitations were performed. Data provide a picture of the thermal quenching processes and activation energy levels. By comparing the photoluminescence from Er ions in the epilayer with a reference sample of Er-doped SiO2, we find that the fraction of Er ions that emits photon at 1.54 μm upon a resonant optical excitation is approximately 68%. This result presents a significant step in the realization of GaN:Er epilayers as an optical gain medium at 1.54 μm.

  13. Threading dislocation annihilation in the GaN layer on cone patterned sapphire substrate

    Xu, S.R., E-mail: [Key Lab of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi’an 710071 (China); Li, P.X. [School of Technical Physics, Xidian University, Xi’an 710071 (China); Zhang, J.C.; Jiang, T. [Key Lab of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi’an 710071 (China); Ma, J.J. [Key Lab of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi’an 710071 (China); School of Technical Physics, Xidian University, Xi’an 710071 (China); Lin, Z.Y.; Hao, Y. [Key Lab of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi’an 710071 (China)


    Highlights: • The LED structure on PSS was grown by MOCVD. • The distribution of defects in GaN film grown on PSS was investigated by TEM. • The main mechanism of TDs reducing on PSS was revealed. - Abstract: The microstructure of an epilayer structure for the blue light-emitting diode grown on a cone patterned sapphire substrate was characterized by high-resolution X-ray diffraction, atomic force microscopy and transmission electron microscopy (TEM). Cross-sectional TEM revealed that most of the dislocations, which originated from planar region, propagated laterally toward the cone region during the lateral growth process. This change of the propagation direction prevented the dislocations from penetrate the epitaxy film and thus principally led to a drastic reduction in the threading dislocation density in GaN films. Particularly, we proposed that the six {11"‾01} semipolar facets play a very important role during the bending process.

  14. Effect of collision cascade density on swelling and surface topography of GaN

    Titov, A.I. [State Polytechnic University, Polytechnicheskaya 29, 195251 St. Petersburg (Russian Federation); Karaseov, P.A., E-mail: [State Polytechnic University, Polytechnicheskaya 29, 195251 St. Petersburg (Russian Federation); Karabeshkin, K.V.; Belyakov, V.S.; Arkhipov, A.V. [State Polytechnic University, Polytechnicheskaya 29, 195251 St. Petersburg (Russian Federation); Kucheyev, S.O. [Lawrence Livermore National Laboratory, Livermore, CA 94551 (United States)


    We study the surface topography and swelling of GaN irradiated at room temperature with 1.3 keV/amu F, P, PF{sub 2}, and PF{sub 4} ions. These irradiation conditions reveal the effect of the collision cascade density on ion-induced swelling and roughening of the GaN surface. Results show that, for F and P ions that create dilute collision cascades, swelling dominates erosion. In the case of molecular ion irradiation, characterized by larger cascade densities, surface erosion dominates swelling. For the conditions studied, surface roughness scales with the thickness of surface amorphous layers when these layers are thinner than about 20 nm.

  15. Radar Waveform Pulse Analysis Measurement System for High-Power GaN Amplifiers

    Thrivikraman, Tushar; Perkovic-Martin, Dragana; Jenabi, Masud; Hoffman, James


    This work presents a measurement system to characterize the pulsed response of high-power GaN amplifiers for use in space-based SAR platforms that require very strict amplitude and phase stability. The measurement system is able to record and analyze data on three different time scales: fast, slow, and long, which allows for greater detail of the mechanisms that impact amplitude and phase stability. The system is fully automated through MATLAB, which offers both instrument control capability and in-situ data processing. To validate this system, a high-power GaN HEMT amplifier operated in saturation was characterized. The fast time results show that variations to the amplitude and phase are correlated to DC supply transients, while long time characteristics are correlated to temperature changes.

  16. Low-threshold GaN thin-film random laser through the weak scattering feedback

    Zhu, Hai; Chen, Anqi; Wu, Yanyan; Ji, Xu; He, Yiting; Qiu, Zhiren; Tang, Zikang; Yu, Siufung


    Room temperature random lasing is demonstrated from a GaN epitaxy film with defect pits that result from growth imperfection. The optical coherence feedback is attributed to the formation of closed-loop paths of light through the scattering effect of the defect pits, which can avoid the difficulty of fabricating an artificial cavity. The random lasing action was also investigated through near and far-field patterns that imaged onto the CCD camera. In addition, the angle distribution of the laser beam was illustrated by use of an angle-resolved spectrometer. The lasing threshold, based on the weak scattering diffusive mode of GaN, is about one order of magnitude lower than that strong scattering random laser (RL). Hence, the results in this paper represent a low-cost technique to realize GaN-based laser diodes without the fabrication difficulty of cavity facets that result from the hardness of the sapphire substrate.

  17. Use of AlGaN in the notch region of GaN Gunn diodes

    Yang, Linan; Hao, Yue; Zhang, Jincheng


    The wurtzite gallium nitride (GaN) Gunn diodes with aluminum gallium nitride (AlGaN) as launcher in the notch region are investigated by negative-differential-mobility model based simulation. Under the operation of self-excitation oscillation with dipole domain mode, the simulations show that the diode with two-step-graded AlGaN launcher structure can yield the maximal rf power of 1.95 W and dc/rf conversion efficiency of 1.72% at the fundamental oscillation frequency of around 215 GHz. This kind of Gunn diode structure without the low doping process is convenient for accurately controlling the dopant concentration of GaN epitaxial growth.

  18. Investigation of yellow luminescence intensity of N-polar unintentionally doped GaN

    Du Da-Chao; Zhang Jin-Cheng; Ou Xin-Xiu; Wang Hao; Chen Ke; Xue Jun-Shuai; Xu Sheng-Rui; Hao Yue


    This paper reports that the yellow luminescence intensity of N-polar GaN Epi-layers is much lower than that of Ga-polar ones due to the inverse polarity, and reduces drastically in the N-polar unintentionally-doped GaN after etching in KOH solution. The ratio of yellow luminescence intensity to band-edge emission intensity decreases sharply with the etching time. The full width at half maximum of x-ray diffraction of (10-12) plane falls sharply after etching, and the surface morphology characterized by scanning electron microscope shows a rough surface that changes with the etching time. The mechanism for the generation of the yellow luminescence are explained in details.

  19. Lattice location and optical activation of rare earth implanted GaN

    Wahl, U; Lorenz, K; Correia, J G; Monteiro, T; De Vries, B; Vantomme, A; Vianden, R


    This paper reviews the current knowledge on rare earths (REs) implanted into GaN with a special focus on their lattice location and on the optical activation by means of thermal annealing. While emission channeling experiments have given information on the lattice location of rare earths following low-dose (around 10$^{13}$ cm$^{-2}$) implantation, both in the as-implanted state and after annealing up to 900°C, the lattice location of higher-dose implants (10$^{14}-10^{15}$ cm$^{-2}$) and their defect annealing behaviour were studied using the Rutherford backscattering/channeling method. The available channeling and luminescence results suggest that the optical activation of implanted REs in GaN is related to their incorporation in substitutional Ga sites combined with the effective removal of the implantation damage.

  20. Demonstration of a High Open-Circuit Voltage GaN Betavoltaic Microbattery

    CHENG Zai-Jun; SAN Hai-Sheng; CHEN Xu-Yuan; LIU Bo; FENG Zhi-Hong


    A high open-circuit voltage betavoltaic microbattery based on a GaN p-i-n diode is demonstrated.Under the irradiation of a 4× 4mm2 planar solid 63Ni source with an activity of 2mCi,the open-circuit voltage Voc of the fabricated single 2x2mm2 cell reaches as high as 1.62 V,the short-circuit current density Jsc is measured to be 16nA/cm2.The microbattery has a fill factor of 55%,and the energy conversion effciency of beta radiation into electricity reaches to 1.13%.The results suggest that GaN is a highly promising potential candidate for long-life betavoltaic microbatteries used as power supplies for microelectromechanical system devices.

  1. Inductively Coupled Plasma-Induced Etch Damage of GaN p-n Junctions



    Plasma-induced etch damage can degrade the electrical and optical performance of III-V nitride electronic and photonic devices. We have investigated the etch-induced damage of an Inductively Coupled Plasma (ICP) etch system on the electrical performance of mesa-isolated GaN pn-junction diodes. GaN p-i-n mesa diodes were formed by Cl{sub 2}/BCl{sub 3}/Ar ICP etching under different plasma conditions. The reverse leakage current in the mesa diodes showed a strong relationship to chamber pressure, ion energy, and plasma flux. Plasma induced damage was minimized at moderate flux conditions ({le} 500 W), pressures {ge}2 mTorr, and at ion energies below approximately -275 V.

  2. Analysis on the semantic evolution of Chinese Gan dialect from the perspective of cognition

    Xiao Jiugen


    Full Text Available The meaning of a word is the reflection of social life, and it is the result of the cognition of the object, phenomenon and relationship through the mental activity. The development and changes of lexical mean-ings essentially reflect the development and change of people’s cognitive activities, so people’s cognitive aware-ness is reflected in words, which is also reflected in the word meaning evolution of Chinese Gan dialect. Whether in the extended way or pattern, the linkage, radiation, complex comprehensive changes of the lexical meaning of Gan dialect in Chinese, all follow a rule: The expression of the meaning in cognitive process will corresponding-ly change with the continuous deepening of human cognition.

  3. Threading dislocation reduction in transit region of GaN terahertz Gunn diodes

    Li, Liang; Yang, Lin-An; Zhang, Jin-Cheng; Xue, Jun-Shuai; Xu, Sheng-Rui; Lv, Ling; Hao, Yue; Niu, Mu-Tong


    An effect of the position of notch-doping layer in 1-μm GaN Gunn diode on threading dislocations (TDs) distribution is investigated by transmission electron microscopy. Compared with the top-notching-layer (TNL) structure, the bottom-notching-layer (BNL) structure can efficiently reduce the TDs density and improve the crystal quality in the transit region of GaN Gunn diode because it exhibits twice-transition of growth mode from atomic step flow to layer-by-layer nucleation and leads to a significant annihilation of TDs before penetrating into the transit region. X-ray diffraction and Raman spectroscopy reveal that the BNL structure has less compressive stress than the TNL structure.

  4. Origin of orange color in nominally undoped HVPE GaN crystals

    Zimmermann, F.; Beyer, F. C.; Gärtner, G.; Röder, C.; Son, N. T.; Janzén, E.; Veselá, D.; Lorinčík, J.; Hofmann, P.; Krupinski, M.; Mikolajick, T.; Habel, F.; Leibiger, G.; Heitmann, J.


    In this article we investigated unintentionally doped (UID) GaN grown by hydride vapor phase epitaxy (HVPE) with respect to point defects and impurity concentration. The samples were orange tinted to different extent. Optical analysis was performed by micro-photoluminescence and absorption spectroscopy. Absorption measurements revealed an absorption peak at 1.5 eV related to an internal transition in Mn3+ impurities and a second band with low energy onset at 1.9 eV, both increasing with the extent of orange color. Electron paramagnetic resonance investigations showed the presence of Mn2+ and Fe3+ in the colored crystals. The overall impurity concentration was verified by secondary ion mass spectrometry. Orange tint is associated with an increase of transition metal contamination, especially Mn. Based on these observations we suggest that the orange coloring in the investigated UID HVPE GaN samples is caused by the presence of Mn impurities.

  5. Arsenic in ZnO and GaN: substitutional cation or anion sites?

    Wahl, Ulrich; Rita, Elisabete; Marques, Ana Claudia; Alves, Eduardo; Carvalho Soares, José


    We have determined the lattice location of ion implanted As in ZnO and GaN by means of conversion electron emission channeling from radioactive $^{73}$As. In contrast to what one might expect from its nature as a group V element, we find that As does not occupy substitutional O sites in ZnO but in its large majority substitutional Zn sites. Arsenic in ZnO is thus an interesting example for an impurity in a semiconductor where the major impurity lattice site is determined by atomic size and electronegativity rather than its position in the periodic system. In contrast, in GaN the preference of As for substitutional cation sites is less pronounced and about half of the implanted As atoms occupy Ga and the other half N sites. Apparently, the smaller size-mismatch between As and N and the chemical similarity of both elements make it feasible that As partly substitutes for N atoms.

  6. Germanium doping of GaN by metalorganic chemical vapor deposition for polarization screening applications

    Young, N.G.


    We demonstrate n-type doping of GaN with Ge by MOCVD at high concentrations that are necessary to fully screen the polarization fields in c-plane InGaN/GaN quantum wells. Hall measurements show linear Ge incorporation with dopant flow rate and carrier concentrations exceeding 1×10 cm. GaN:Ge layers exhibit excellent electron mobility, high conductivity, and contact resistivity comparable to the best unannealed contacts to Si-doped GaN. However, the surface morphology begins to degrade with Ge concentrations above 1×10 cm, resulting in severe step bunching and a network of plateaus and trenches, even in layers as thin as 10 nm.

  7. Vacancy complexes induce long-range ferromagnetism in GaN

    Zhang, Zhenkui


    By means of density functional theory, we argue that ferromagnetism in GaN can be induced by vacancy complexes. Spin polarization originates from the charge compensation between neutral N and Ga vacancies. Defect formation energy calculations predict that a vacancy complex of two positively charged N vacancies and one doubly negative Ga vacancy is likely to form. This defect complex induces a net moment of 1 μB, which is localized around the negative Ga center and exhibits pronounced in-plane ferromagnetic coupling. In contrast to simple Ga vacancy induced ferromagnetism, the proposed picture is in line with the fact that N vacancies have a low formation energy. Formation energies indicate mutual stabilization of the intrinsic defects in GaN.

  8. Spin diffusion in bulk GaN measured with MnAs spin injector

    Jahangir, Shafat


    Spin injection and precession in bulk wurtzite n-GaN with different doping densities are demonstrated with a ferromagnetic MnAs contact using the three-terminal Hanle measurement technique. Theoretical analysis using minimum fitting parameters indicates that the spin accumulation is primarily in the n-GaN channel rather than at the ferromagnet (FM)/semiconductor (SC) interface states. Spin relaxation in GaN is interpreted in terms of the D’yakonov-Perel mechanism, yielding a maximum spin lifetime of 44 ps and a spin diffusion length of 175 nm at room temperature. Our results indicate that epitaxial ferromagnetic MnAs is a suitable high-temperature spin injector for GaN.

  9. Defect-impurity complex induced long-range ferromagnetism in GaN nanowires

    Assa Aravindh, S


    Present work investigates the structural, electronic and magnetic properties of Gd doped wurtzite GaN nanowires (NWs) oriented along the [0001] direction in presence of intrinsic defects by employing the GGA + U approximation. We find that Ga vacancy (VGa) exhibits lower formation energy compared to N vacancy. Further stabilization of point defects occurs due to the presence of Gd. The strength of ferromagnetism (FM) increases by additional positive charge induced by the VGa. Electronic structure analysis shows that VGa introduces defect levels in the band gap leading to ferromagnetic coupling due to the hybridization of the p states of the Ga and N atoms with the Gd d and f states. Ferromagnetic exchange coupling energy of 76.4 meV is obtained in presence of Gd-VGa complex; hence, the FM is largely determined by the cation vacancy-rare earth complex defects in GaN NWs.

  10. High quality factor two dimensional GaN photonic crystal cavity membranes grown on silicon substrate

    Vico Triviño, N.; Rossbach, G.; Dharanipathy, U.; Levrat, J.; Castiglia, A.; Carlin, J.-F.; Atlasov, K. A.; Butté, R.; Houdré, R.; Grandjean, N.


    We report on the achievement of freestanding GaN photonic crystal L7 nanocavities with embedded InGaN/GaN quantum wells grown by metal organic vapor phase epitaxy on Si (111). GaN was patterned by e-beam lithography, using a SiO2 layer as a hard mask, and usual dry etching techniques. The membrane was released by underetching the Si (111) substrate. Micro-photoluminescence measurements performed at low temperature exhibit a quality factor as high as 5200 at ˜420 nm, a value suitable to expand cavity quantum electrodynamics to the near UV and the visible range and to develop nanophotonic platforms for biofluorescence spectroscopy.

  11. Rare earths in GaN and ZnO studied with the PAC method; Seltene Erden in GaN und ZnO untersucht mit der PAC-Methode

    Nedelec, R.


    The present thesis deals with the implantation and annealing behaviour of two examples of large-band-gap semiconductors GaN and ZnO. The studies begin with the annealing behaviour of GaN after the implantation of {sup 172}Lu. For GaN the annealing process begins at low temperatures with the decreasing of the damping of the lattice frequency. At essentially higher temperatures finally the substitunial contribution increases. This behaviour is also observed for other probe nuclei in GaN. For ZnO the behaviour at low temperature is different. Both for {sup 172}Lu and for {sup 181}Hf the damping is already after the implantation very low. The increasement of the substitutional contribution occurs like in GaN at higher temperatures. Thereafter for GaN and ZnO PAC spectra were token up at different measurement temperatures between 25 and 873 K. For {sup 172}Lu in GaN and in ZnO a strong temperature dependence of the lattice field gradient was observed. Also for {sup 181}Hf in ZnO a strong temperature dependence is observed. For {sup 172}Lu by means of a model for the interaction of quadrupole moments of electronic shells with the nucleus a lattice field gradient of {+-}5.9.10{sup 15} Vcm{sup -2} could be determined. For {sup 172}Lu in ZnO the model yields at 293 K a lattice field gradient of +14.10{sup 15} Vcm{sup -2} respectively -13.10{sup 15} Vcm{sup -2}. The corrsponding measurement with {sup 181}Hf yields a lattice field gradient of {+-}5.7.10{sup 15} Vcm{sup -2}.

  12. Structures and optical properties of \\text{H}_{2}^{+} -implanted GaN epi-layers

    Li, B. S.; Wang, Z. G.


    The implantation damage build-up and optical properties of GaN epitaxial films under \\text{H}2+ ion implantation have been investigated by a combination of Rutherford backscattering in channeling geometry, Raman spectroscopy, UV-visible spectroscopy and transmission electron microscopy. GaN epitaxial films were implanted with 134 keV \\text{H}2+ ions to doses ranging from 3.75   ×   1016 to 1.75   ×   1017 \\text{H}2+  cm-2 at room temperature or the same dose of 1.5   ×   1017 \\text{H}2+  cm-2 at room temperature, 573 and 723 K. The dependence of lattice disorder induced by \\text{H}2+ -implantation on the ion dose can be divided into a three-step damage process. A strong influence of the H concentration on the defect accumulation is discussed. The decrease in relative Ga disorder induced by \\text{H}2+ -implantation is linear with increasing implantation temperature. The absorption coefficient of GaN epitaxial films increases with increasing ion dose, leading to the decrease in Raman scattering spectra of Ga-N vibration. With increasing implantation doses up to 5   ×   1016 \\text{H}2+  cm-2, nanoscale hydrogen bubbles are observed in the H deposition peak region. Interstitial-type dislocation loops are observed in the damaged layer located near the damage peak region, and the geometry of the dislocation loops produced by H implantation is analyzed. The surface layer is almost free of lattice disorder induced by \\text{H}2+ -implantation.

  13. Cubic GaN quantum dots : growth, characterization and integration in microcavities


    In den kubischen Gruppe III-Nitriden existieren, verglichen mit der hexagonalen Phase, keine internen Polarisationsfelder. Daraus ergeben sich in niedrig dimensionalen Systemen wie Quantenpunkten (QP) entscheidende Vorteile. In dieser Arbeit wurden kubische GaN QP in kubischen AlN (k-AlN) Barrieren, mittels plasmaunterstützter Molekularstrahlepitaxie auf 3C-SiC/Si (001) Substraten hergestellt. Eine Analyse der Größen- und Dichteverteilungen der QP identifizierte den verspannungsinduzierten St...

  14. Growth of Single Crystals and Fabrication of GaN and AlN Wafers


    in nature and thus must be synthesized. Crystal growth of this group using standard methods ( Czochralski , Bridgman) is extremely difficult because of...reaction zone in which deposition occurs. High growth rates of up to 0.5 mm/h were obtained with this method ; however, the crystals grew only for short...Chapter Five presents the growth of GaN on sapphire with a modified sandwich growth method which is a variation of vapor phase transport process. Optimum

  15. Hafnium nitride buffer layers for growth of GaN on silicon

    Armitage, Robert D.; Weber, Eicke R.


    Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 {character pullout}m. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

  16. First-principle investigations on the structural dynamics of Ti{sub 2}GaN

    Yang, Z.J., E-mail: [School of Science, Zhejiang University of Technology, Hangzhou 310023 (China); Li, J. [School of Material and Chemical Engineering, Hainan University, Key Laboratory of Ministry of Education for Application Technology of Chemical Materials in Hainan Superior Resources, Haikou 570228 (China); Linghu, R.F. [School of Physics, Guizhou Normal College, Guiyang 550018 (China); Cheng, X.L.; Yang, X.D. [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China)


    Highlights: •Our calculated lattice parameter of Ti{sub 2}GaN shows that c axis is always stiffer than a axis. •The elastic constants investigations demonstrated that the Ti{sub 2}GaN is meta-stable between 350 and 600 GPa. •We observed an abnormal c-axis expansion behavior within 350–600 GPa resulting from the expansion of the Ti–Ti bond length and the increase of the Ti–Ti bond populations. •Study on the density of states we found that the Ti s and p electrons shift towards higher energies with pressure. -- Abstract: We report a first-principle study on the elastic and electronic properties of the nanolaminate Ti{sub 2}GaN. Our calculated lattice parameter shows that c axis is always stiffer than a axis. The elastic constants investigations demonstrated that Ti{sub 2}GaN is stable over a wide pressure range of 0–1000 GPa with the only exception of 350–600 GPa owing to the elastic softening. The softening behaviors of the Young’s and shear moduli are also found in the same pressure range of 350–600 GPa, indicating a structural metastability. Investigation on the axial compressibility we observed an abnormal c-axis expansion behavior within a pressure range of 350–600 GPa, resulting from the expansion of the Ti–Ti bond length and the increase of the Ti–Ti bond population. Study on the density of states (DOSs) we found that the Ti s and Ti p electrons shift towards higher energies with pressure.

  17. Controlled growth of hexagonal GaN pyramids and InGaN QDs

    Lundskog, Anders


    Gallium-nitride (GaN) and its related alloys are direct band gap semiconductors, with a wide variety of applications. The white light emitting diode (LED) is of particular importance as it is expected to replace energy inefficient light bulb and hazardous incandescent lamps used today. However, today’s planar hetero epitaxial grown LEDs  structures contain an unavoidable number of dislocations, which serves as non-radiative recombination centers. The dislocations harm the luminous efficiency ...

  18. Taevo Gans : "Alati on võimalusi rohkem kui üks" / Gitte Hint

    Hint, Gitte


    Taevo Gans (sünd. 1941) kodumaiste materjalide ja tootjate eelistamisest, sisearhitekti valikust, proportsiooni- ja värvitaju vajalikkusest sisekujunduse loomisel, oma eelistustest ruumikujunduses jm. T. Gansist, osalemisest mööbli- ja sisustusmessidel, 1991. a. loodud perefirmast Stuudio Gadis AS, omistatud preemiad, teostatud interjööri ja mööbli projektid aastatel 1968-2002. Ill.: foto T. Gansist

  19. GaN nanowire tip for high aspect ratio nano-scale AFM metrology (Conference Presentation)

    Behzadirad, Mahmoud; Dawson, Noel; Nami, Mohsen; Rishinaramangalam, Ashwin K.; Feezell, Daniel F.; Busani, Tito L.


    In this study we introduce Gallium Nitride (GaN) nanowire (NW) as high aspect ratio tip with excellent durability for nano-scale metrology. GaN NWs have superior mechanical property and young modulus compare to commercial Si and Carbon tips which results in having less bending issue during measurement. The GaN NWs are prepared via two different methods: i) Catalyst-free selected area growth, using Metal Organic Chemical Vapor Deposition (MOCVD), ii) top-down approach by employing Au nanoparticles as the mask material in dry-etch process. To achieve small diameter tips, the semipolar planes of the NWs grown by MOCVD are etched using AZ400k. The diameter of the NWs fabricated using the top down process is controlled by using different size of nanoparticles and by Inductively Coupled Plasma etching. NWs with various diameters were manipulated on Si cantilevers using Focus Ion Beam (FIB) to make tips for AFM measurement. A Si (110) substrate containing nano-scale grooves with vertical 900 walls were used as a sample for inspection. AFM measurements were carried out in tapping modes for both types of nanowires (top-down and bottom-up grown nanowires) and results are compared with conventional Si and carbon nanotube tips. It is shown our fabricated tips are robust and have improved edge resolution over conventional Si tips. GaN tips made with NW's fabricated using our top down method are also shown to retain the gold nanoparticle at tip, which showed enhanced field effects in Raman spectroscopy.

  20. Space-and-time-resolved spectroscopy of single GaN nanowires

    Upadhya, Prashanth C. [Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Laboratory for Electro-Optics Systems, Indian Space Research Organization, Bangalore 560058 (India); Martinez, Julio A. [Sandia National Laboratories, P.O. Box 5800, MS-1086, Albuquerque, New Mexico 87185 (United States); Department of Chemical and Materials Engineering, New Mexico State University, Las Cruces, New Mexico 88003 (United States); Li, Qiming; Wang, George T.; Swartzentruber, Brian S. [Sandia National Laboratories, P.O. Box 5800, MS-1086, Albuquerque, New Mexico 87185 (United States); Taylor, Antoinette J.; Prasankumar, Rohit P., E-mail: [Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)


    Gallium nitride nanowires have garnered much attention in recent years due to their attractive optical and electrical properties. An understanding of carrier transport, relaxation, and recombination in these quasi-one-dimensional nanosystems is therefore important in optimizing them for various applications. Here, we present ultrafast optical microscopic measurements on single GaN nanowires. Our experiments, performed while varying the light polarization, excitation fluence, and position, give insight into the mechanisms governing carrier dynamics in these nanosystems.

  1. Proton irradiation induced defects in GaN: Rutherford backscattering and thermally stimulated current studies

    Nakamura, T.; Nishikata, N.; Kamioka, K.; Kuriyama, K.; Kushida, K.


    The proton irradiation induced defects in GaN are studied by combining elastic recoil detection analysis (ERDA), thermally stimulated current (TSC), and Rutherford backscattering spectroscopy (RBS) measurements. The proton irradiation (peak concentration: 1.0 × 1015 cm-2) into GaN films with a thickness of 3 μm is performed using a 500 keV implanter. The proton concentration by a TRIM simulation is maximum at 3600 nm in depth, which means that the proton beam almost passes through the GaN film. The carrier concentration decreases three orders of magnitude to 1015 cm-3 by the proton irradiation, suggesting the existence of the proton irradiation-induced defects. The ERDA measurements using the 1.5 MeV helium beam can evaluate hydrogen from the surface to ∼300 nm. The hydrogen concentration at ∼220 nm is ∼8.3 × 1013 cm-2 and ∼1.0 × 1014 cm-2 for un-irradiated and as-irradiated samples, respectively, suggesting that electrical properties are almost not affected by hydrogen. TSC measurements show a broad spectrum at around 110 K which can be divided into three traps, P1 (ionization energy 173 meV), P2 (251 meV), and P3 (330 meV). The peak intensity of P1 is much larger than that of P2 and P3. These traps are related to the N vacancy and/or complex involving N vacancy (P1), neutral Ga vacancy (VGa) (P2), and complex involving VGa (P3). The Ga displacement concentration evaluated by RBS measurements is 1.75 × 1019 cm-3 corresponding to 1/1000 of the Ga concentration in GaN. The observed Ga displacement may be origins of P2 and P3 traps.


    Frolov, D. [Fermilab; Pfeffer, H. [Fermilab; Saewert, G. [Fermilab


    Using recently available GaN FETs, a 600 Volt three- stage, multi-FET switch has been developed having 2 nanosecond rise time driving a 200 Ohm load with the potential of approaching 30 MHz average switching rates. Possible applications include driving particle beam choppers kicking bunch-by-bunch and beam deflectors where the rise time needs to be custom tailored. This paper reports on the engineering issues addressed, the design approach taken and some performance results of this switch.

  3. 4th Optimization Day

    Eberhard, Andrew; Ralph, Daniel; Glover, Barney M


    Although the monograph Progress in Optimization I: Contributions from Aus­ tralasia grew from the idea of publishing a proceedings of the Fourth Optimiza­ tion Day, held in July 1997 at the Royal Melbourne Institute of Technology, the focus soon changed to a refereed volume in optimization. The intention is to publish a similar book annually, following each Optimization Day. The idea of having an annual Optimization Day was conceived by Barney Glover; the first of these Optimization Days was held in 1994 at the University of Ballarat. Barney hoped that such a yearly event would bring together the many, but widely dispersed, researchers in Australia who were publishing in optimization and related areas such as control. The first Optimization Day event was followed by similar conferences at The University of New South Wales (1995), The University of Melbourne (1996), the Royal Melbourne Institute of Technology (1997), and The University of Western Australia (1998). The 1999 conference will return to Ballarat ...

  4. Structural and optical properties of vanadium ion-implanted GaN

    Macková, A.; Malinský, P.; Jagerová, A.; Sofer, Z.; Klímová, K.; Sedmidubský, D.; Mikulics, M.; Lorinčík, J.; Veselá, D.; Böttger, R.; Akhmadaliev, S.


    The field of advanced electronic and optical devices searches for a new generation of transistors and lasers. The practical development of these novel devices depends on the availability of materials with the appropriate magnetic and optical properties, which is strongly connected to the internal morphology and the structural properties of the prepared doped structures. In this contribution, we present the characterisation of V ion-doped GaN epitaxial layers. GaN layers, oriented along the (0 0 0 1) crystallographic direction, grown by low-pressure metal-organic vapour-phase epitaxy (MOVPE) on c-plane sapphire substrates were implanted with 400 keV V+ ions at fluences of 5 × 1015 and 5 × 1016 cm-2. Elemental depth profiling was accomplished by Rutherford Backscattering Spectrometry (RBS) and Secondary Ion Mass Spectrometry (SIMS) to obtain precise information about the dopant distribution. Structural investigations are needed to understand the influence of defect distribution on the crystal-matrix recovery and the desired structural and optical properties. The structural properties of the ion-implanted layers were characterised by RBS-channelling and Raman spectroscopy to get a comprehensive insight into the structural modification of implanted GaN and to study the influence of subsequent annealing on the crystalline matrix reconstruction. Photoluminescence measurement was carried out to check the optical properties of the prepared structures.

  5. Ultraviolet Laser SQUID Microscope for GaN Blue Light Emitting Diode Testing

    Daibo, M [Department of Electrical and Electronic Engineering, Faculty of Engineering, Iwate University, Morioka 020-8551 (Japan); Kamiwano, D [Graduate School of Engineering, Iwate University, Morioka 020-8551 (Japan); Kurosawa, T [Graduate School of Engineering, Iwate University, Morioka 020-8551 (Japan); Yoshizawa, M [Graduate School of Engineering, Iwate University, Morioka 020-8551 (Japan); Tayama, N [Department of Electrical and Electronic Engineering, Faculty of Engineering, Iwate University, Morioka 020-8551 (Japan)


    We carried out non-contacting measurements of photocurrent distributions in GaN blue light emitting diode (LED) chips using our newly developed ultraviolet (UV) laser SQUID microscope. The UV light generates the photocurrent, and then the photocurrent induces small magnetic fields around the chip. An off-axis arranged HTS-SQUID magnetometer is employed to detect a vector magnetic field whose typical amplitude is several hundred femto-tesla. Generally, it is difficult to obtain Ohmic contacts for p-type GaN because of the low hole concentration in the p-type epitaxial layer and the lack of any available metal with a higher work function compared with the p-type GaN. Therefore, a traditional probecontacted electrical test is difficult to conduct for wide band gap semiconductors without an adequately annealed electrode. Using the UV-laser SQUID microscope, the photocurrent can be measured without any electrical contact. We show the photocurrent vector map which was reconstructed from measured magnetic fields data. We also demonstrate how we found the position of a defect of the electrical short circuits in the LED chip.

  6. Magnetic Characteristics of Mn-Implanted GaN Nanorods Followed by Thermal Annealing

    Im Taek Yoon


    Full Text Available We have investigated the magnetic and optical properties of dislocation-free vertical GaN nanorods with diameters of 150 nm grown on (111 Si substrates by radio-frequency plasma-assisted molecular-beam epitaxy followed by Mn ion implantation and annealing. The GaN nanorods are fully relaxed and have a very good crystal quality characterized by extremely strong and narrow photoluminescence excitonic lines near 3.47 eV. For GaMnN nanorods, it can be concluded that the ferromagnetic property of GaMnN nanorod with a Curie temperature over 300 K is associated with the formation of Mn4Si7 magnetic phase which results from the effects of magnetic and structural disorder introduced by a random incorporation and inhomogeneous distribution of Mn atoms in the porous layer between the nanorods that form precipitates in the Si substrate before or during the annealing step amongst the GaN nanorods.

  7. The influence of growth temperatures on the characteristics of GaN nanowires: The Raman study

    Tan, L.K., E-mail:; Yam, F.K.; Low, L.L.; Beh, K.P.; Hassan, Z.


    The study of Raman scattering of GaN nanowires under different growth temperatures (750 °C to 1000 °C) is presented. GaN nanowires grown at 950 °C possessed the highest crystallinity. The Raman measurement illustrated E{sub 2}(high) mode experienced a blueshift at lower temperature and redshift with the rising growth temperatures. This was related to the presence of stress/strain and the considerable oxygen content in the nanowires. By using Raman line shape analysis, the carrier concentration and mobility at different growth temperatures were determined which varied in the range of 4.0×10{sup 16} cm{sup −3} to 5.27×10{sup 17} cm{sup −3} and 158.2 cm{sup 2}/V s to 376.2 cm{sup 2}/V s, respectively. A comparative analysis of GaN thin film and nanowires revealed that the decreasing dimension of nanowires caused the broadening and lower frequency shift of Raman spectrum.

  8. The structural and optical properties of metal ion-implanted GaN

    Macková, A.; Malinský, P.; Sofer, Z.; Šimek, P.; Sedmidubský, D.; Veselý, M.; Böttger, R.


    The practical development of novel optoelectronic materials with appropriate optical properties is strongly connected to the structural properties of the prepared doped structures. We present GaN layers oriented along the (0 0 0 1) crystallographic direction that have been grown by low-pressure metal-organic vapour-phase epitaxy (MOVPE) on sapphire substrates implanted with 200 keV Co+, Fe+ and Ni+ ions. The structural properties of the ion-implanted layers have been characterised by RBS-channelling and Raman spectroscopy to obtain a comprehensive insight into the structural modification of implanted GaN layers and to study the subsequent influence of annealing on crystalline-matrix recovery. Photoluminescence was measured to control the desired optical properties. The post-implantation annealing induced the structural recovery of the modified GaN layer depending on the introduced disorder level, e.g. depending on the ion implantation fluence, which was followed by structural characterisation and by the study of the surface morphology by AFM.

  9. Reduction of crack density in ammonothermal bulk GaN growth

    Letts, Edward; Key, Daryl; Hashimoto, Tadao


    The growth of high quality GaN by the ammonothermal method is appealing due to the potential to scale and achieve very high crystal quality. Several applications could benefit from the supply of very high quality GaN such as high power light emitting diodes, laser diodes, and high power electronics. Despite steady advancement by the few groups developing ammonothermal growth technology, high quality ammonothermal GaN wafers have yet be manufactured in great quantities. This paper reviews the current progress of ammonothermal growth at SixPoint Materials. Growths were performed at TX-ray diffraction was carried out on an ammonothermally grown boule at 90 points along a 44 mm line providing a mean (002) and (201) full width half max (FWHM) reflection of 29 and 35″ respectively using a beam spot of 0.3 mm x 0.3 mm and an open detector. The radius of curvature is typically between 3 and 20 m across the sample. Dislocation densities are routinely low 105 cm-2 .

  10. Raman scattering studies on manganese ion-implanted GaN

    Xu Da-Qing; Zhang Yi-Men; Zhang Yu-Ming; Li Pei-Xian; Wang Chao


    This paper reports that the Raman spectra have been recorded on the metal-organic chemical vapour deposition epitaxially grown GaN before and after the Mn ions implanted.Several Raman defect modes have emerged from the implanted samples.The structures around 182 cm-1 modes are attributed to the disorder-activated Raman scattering,whereas the 361 cm-1 and 660 cm-1 peaks are assigned to nitrogen vacancy-related defect scattering.One additional peak at 280 cm-1 is attributed to the vibrational mode of gallium vacancy-related defects and/or to disorder activated Raman scattering.A Raman-scattering study of lattice recovery is also presented by rapid thermal annealing at different temperatures between 700℃ and 1050℃ on Mn implanted GaN epilayers.The behaviour of peak-shape change and full width at half maximum(FWHM)of the A1(LO)(733 cm-1)and EH2(566 cm-1)Raman modes are explained on the basis of implantation-induced lattice damage in GaN epilayers.

  11. Polarized infrared reflectance study of free standing cubic GaN grown by molecular beam epitaxy

    Lee, S.C., E-mail: [Nano-Optoelectronics Research Laboratory, School of Physics, Universiti Sains Malaysia, 11800 Penang (Malaysia); Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur (Malaysia); Ng, S.S.; Hassan, H. Abu; Hassan, Z.; Zainal, N. [Nano-Optoelectronics Research Laboratory, School of Physics, Universiti Sains Malaysia, 11800 Penang (Malaysia); Novikov, S.V.; Foxon, C.T.; Kent, A.J. [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom)


    Optical properties of free standing cubic gallium nitride grown by molecular beam epitaxy system are investigated by a polarized infrared (IR) reflectance technique. A strong reststrahlen band, which reveals the bulk-like optical phonon frequencies, is observed. Meanwhile, continuous oscillation fringes, which indicate the sample consists of two homogeneous layers with different dielectric constants, are observed in the non-reststrahlen region. By obtaining the first derivative of polarized IR reflectance spectra measured at higher angles of incidence, extra phonon resonances are identified at the edges of the reststrahlen band. The observations are verified with the theoretical results simulated based on a multi-oscillator model. - Highlights: • First time experimental studies of IR optical phonons in bulk like, cubic GaN layer. • Detection of extra phonon modes of cubic GaN by polarized IR reflectance technique. • Revelation of IR multiphonon modes of cubic GaN by first derivative numerical method. • Observation of multiphonon modes requires very high angle of incidence. • Resonance splitting effect induced by third phonon mode is a qualitative indicator.

  12. Chlorine-free plasma-based vapour growth of GaN

    Siche, D.; Kachel, K.; Zwierz, R.; Golka, S.; Sudhoff, P.; Gogova, D. [Leibniz-Institut fuer Kristallzuechtung, Berlin (Germany); Vodopyanov, A.; Izotov, I.; Sennikov, P.; Golubev, S. [Institute of Applied Physics, Nizhny Novgorod (Russian Federation); Franke, K.P. [Institute fuer Umwelttechnologien GmbH, Berlin (Germany)


    In pure physical vapour transport process for GaN growth, the liquid Ga source has to be kept at temperatures about 1300-1400 C to provide sufficient Ga vapour pressure for reasonably large growth rates. The growth temperature needs to be slightly lower to prevent droplet formation in the Ga vapour. At such high temperatures, however, the early ammonia decomposition prevents the favorable growth with reactive nitrogen in excess. The vapour processes under development in this study aim at overcoming the drawbacks of the reaction of physically or chemically transported Ga and ammonia. For this purpose, the reactive nitrogen will be supplied by plasma excitation of N{sub 2}. First, the results on ammonia-based GaN growth and their disadvantages are discussed. Then, the challenges in designing of a new type of plasma sources (a microwave and a dielectric barrier discharge) and the first experimental results on the ammonia-free process development are presented. The microwave approach seems to be very promising in terms of GaN growth. It has higher growth rates than the dielectric barrier discharge method and therefore it is more cost-effective. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Theoretical and experimental study of dynamics of photoexcited carriers in GaN

    Shishehchi, Sara; Bellotti, Enrico, E-mail: [ECE Department, Boston University, 8 Saint Mary' s Street, Boston, Massachusetts 02215 (United States); Rudin, Sergey; Garrett, Gregory A.; Wraback, Michael [Sensors and Electron Devices Directorate, US Army Research Laboratory, 2800 Powder Mill Rd, Adelphi, Maryland 20783 (United States)


    We present a theoretical and experimental study of the sub-picosecond dynamics of photo-excited carriers in GaN. In the theoretical model, interaction with an external ultrafast laser pulse is treated coherently and to account for the scattering mechanisms and dephasing processes, a generalized Monte-Carlo simulation is used. The scattering mechanisms included are carrier interactions with polar optical phonons and acoustic phonons, and carrier-carrier Coulomb interactions. We study the effect of different scattering mechanisms on the carrier densities. In the case that the excitation energy satisfies the threshold for polar optical scattering, phonon contribution is the dominant process in relaxing the system, otherwise, carrier-carrier mechanism is dominant. Furthermore, we present the temperature and pulse power dependent normalized luminescence intensity. The results are presented over a range of temperatures, electric field, and excitation energy of the laser pulse. For comparison, we also report the experimental time-resolved photoluminescence studies on GaN samples. There is a good agreement between the simulation and experiment in normalized luminescence intensity results. Therefore, we show that we can explain the dynamics of the photo-excited carriers in GaN by including only carrier-carrier and carrier-phonon interactions and a relatively simple two-band electronic structure model.

  14. Study of the defects in GaN epitaxial films grown on sapphire by HVPE

    Liu, Zhanhui; Xiu, Xiangqian; Chen, Lin; Zhang, Rong; Xie, Zili; Han, Ping; Shi, Yi; Gu, Shulin; Zheng, Youdou


    In this paper, the defects in hexagonal GaN epitaxial layers grown on (0001) sapphire (Al IIO 3) substrates by HVPE with a horizontal tube reactor had been studied. The GaN epitaxial layers were etched by means of defect-selective etching (Orthodox etching in molten KOH). The samples were characterized by Scanning Electron Microscopy (SEM) and Cathodoluminescence spectra (CL). From surface morphology and cross-sectional images, the defects could be divided into various types: cracks, low angle grain boundary (LAGB), nano-pipes and dislocations. These different defects were discussed. The cracks were proposed as related to the strain. And the strain could not only come from the lattice mismatch and thermal mismatch between sapphire and GaN layer in their interface, but also from the HVPE growth process. It was found that these screw, mixed and edge type dislocations formed small hexagonal pits after etching. Some pits would be observed in the area near LAGB. Additionally, by CL mapping technique, some non-radiative recombination centers without surface terminations could be probed optically.

  15. Ruthenium adsorption and diffusion on the GaN(0 0 0 1) surface

    Ortega Lopez, Cesar [Departamento de Fisica, Universidad de Cordoba, Monteria (Colombia); GEMA, Departamento de Fisica, Universidad Nacional de Colombia, A.A. 5997 Bogota (Colombia); Lopez Perez, William [GFMC, Departamento de Fisica, Universidad del Norte, A.A. 1569 Barranquilla (Colombia)], E-mail:; Rodriguez M, Jairo Arbey [GEMA, Departamento de Fisica, Universidad Nacional de Colombia, A.A. 5997 Bogota (Colombia)


    We report first principles calculations to analyze the ruthenium adsorption and diffusion on GaN(0 0 0 1) surface in a 2x2geometry. The calculations were performed using the generalized gradient approximation (GGA) with ultrasoft pseudopotential within the density functional theory (DFT). The surface is modeled using the repeated slabs approach. To study the most favorable ruthenium adsorption model we considered T{sub 1}, T{sub 4} and H{sub 3} special sites. We find that the most energetically favorable structure corresponds to the Ru- T{sub 4} model or the ruthenium adatom located at the T{sub 4} site, while the ruthenium adsorption on top of a gallium atom (T{sub 1} position) is totally unfavorable. The ruthenium diffusion on surface shows an energy barrier of 0.612 eV. The resultant reconstruction of the ruthenium adsorption on GaN(0 0 0 1)- 2x2 surface presents a lateral relaxation of some hundredth of A in the most stable site. The comparison of the density of states and band structure of the GaN(0 0 0 1) surface without ruthenium adatom and with ruthenium adatom is analyzed in detail.

  16. Optical characteristics of wet-thermally oxidized bulk and nanoporous GaN

    Kim, Sinjae; Kadam, Mahadev; Kang, Jin-Ho; Ryu, Sang-Wan


    Gallium nitride (GaN) films deposited on sapphire substrates by metal organic chemical vapor deposition were successfully transformed into bulk and nanoporous gallium oxide (Ga2O3) using a wet thermal oxidation technique. Oxidation depth measurements confirmed that the oxide growth appeared to be faster in the case of nanoporous GaN than that of bulk GaN. Spectroscopic ellipsometry was used to evaluate and compare the optical properties of nanoporous and bulk Ga2O3 films, such as refractive index and extinction coefficient, which revealed improved optical properties for nanoporous Ga2O3 compared to the bulk. The simulations conducted on the ellipsometric spectra for bulk and nanoporous Ga2O3 using the Forouhi-Bloomer model and the Bruggeman effective medium approximation revealed the best fit with a low mean square error value. In the case of nanoporous Ga2O3, zero absorption was observed in the wavelength range of 300 nm to 840 nm, supporting the use of this material as a transparent coating in optoelectronic devices.

  17. Valence band hybridization in N-rich GaN1-xAsx alloys

    Wu, J.; Walukiewicz, W.; Yu, K.M.; Denlinger, J.D.; Shan, W.; Ager III, J.W.; Kimura, A.; Tang, H.F.; Kuech, T.F.


    We have used photo-modulated transmission and optical absorption spectroscopies to measure the composition dependence of interband optical transitions in N-rich GaN{sub 1-x}As{sub x} alloys with x up to 0.06. The direct bandgap gradually decreases as x increases. In the dilute x limit, the observed band gap approaches 2.8 eV; this limiting value is attributed to a transition between the As localized level, which has been previously observed in As-doped GaN at 0.6 eV above the valence band maximum in As-doped GaN, and the conduction band minimum. The structure of the valence band of GaN{sub 1-x}As{sub x} is explained by the hybridization of the localized As states with the extended valence band states of GaN matrix. The hybridization is directly confirmed by soft x-ray emission experiments. To describe the electronic structure of the GaN{sub 1-x}As{sub x} alloys in the entire composition range a linear interpolation is used to combine the effects of valence band hybridization in N-rich alloys with conduction band anticrossing in As-rich alloys.

  18. A Ka-band 22 dBm GaN amplifier MMIC

    Wang Dongfang; Chen Xiaojuan; Yuan Tingting; Wei Ke; Liu Xinyu


    A Ka-band GaN amplifier MMIC has been designed in CPW technology,and fabricated with a domestic GaN epitaxial wafer and process.This is,to the best of our knowledge,the first demonstration of domestic Kaband GaN amplifier MMICs.The single stage CPW MMIC utilizes an AIGaN/GaN HEMT with a gate-length of 0.25 μm and a gate-width of 2 × 75 μm.Under Vds =10 V,continuous-wave operating conditions,the amplifier has a 1.5 GHz operating bandwidth.It exhibits a linear gain of 6.3 dB,a maximum output power of 22 dBm and a peak PAE of 9.5% at 26.5 GHz.The output power density of the AIGaN/GaN HEMT in the MMIC reaches 1 W/mm at Ka-band under the condition of Vds =10 V.

  19. Mechanical Deformation Induced in Si and GaN Under Berkovich Nanoindentation

    Jian Sheng-Rui


    Full Text Available AbstractDetails of Berkovich nanoindentation-induced mechanical deformation mechanisms of single-crystal Si(100 and the metal-organic chemical-vapor deposition (MOCVD derived GaN thin films have been systematic investigated by means of micro-Raman spectroscopy and cross-sectional transmission electron microscopy (XTEM techniques. The XTEM samples were prepared by using focused ion beam (FIB milling to accurately position the cross-section of the nanoindented area. The behaviors of the discontinuities displayed in the loading and unloading segments of the load-displacement curves of Si and GaN thin films performed with a Berkovich diamond indenter tip were explained by the observed microstructure features obtained from XTEM analyses. According to the observations of micro-Raman and XTEM, the nanoindentation-induced mechanical deformation is due primarily to the generation and propagation of dislocations gliding along the pyramidal and basal planes specific to the hexagonal structure of GaN thin films rather than by indentation-induced phase transformations displayed in Si.

  20. Olefin metathesis reaction on GaN (0 0 0 1) surfaces

    Makowski, Matthew S.; Zemlyanov, Dmitry Y.; Ivanisevic, Albena


    Proof-of-concept reactions were performed on GaN (0 0 0 1) surfaces to demonstrate surface termination with desired chemical groups using an olefin cross-metathesis reaction. To prepare the GaN surfaces for olefin metathesis, the surfaces were hydrogen terminated with hydrogen plasma, chlorine terminated with phosphorous pentachloride, and then terminated with an alkene group via a Grignard reaction. The olefin metathesis reaction then bound 7-bromo-1-heptene. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy, and water contact angle measurements following each step in the reaction scheme. The XPS data was used to qualitatively identify surface chemical species and to quantitatively determine molecular surface coverage. The bromine atom in 7-bromo-1-heptene served as a heteroatom for identification with XPS. The reaction scheme resulted in GaN substrates with a surface coverage of 0.10 monolayers and excellent stability towards oxidation when exposed to oxygen plasma.

  1. Theoretical and experimental study of dynamics of photoexcited carriers in GaN

    Shishehchi, Sara; Rudin, Sergey; Garrett, Gregory A.; Wraback, Michael; Bellotti, Enrico


    We present a theoretical and experimental study of the sub-picosecond dynamics of photo-excited carriers in GaN. In the theoretical model, interaction with an external ultrafast laser pulse is treated coherently and to account for the scattering mechanisms and dephasing processes, a generalized Monte-Carlo simulation is used. The scattering mechanisms included are carrier interactions with polar optical phonons and acoustic phonons, and carrier-carrier Coulomb interactions. We study the effect of different scattering mechanisms on the carrier densities. In the case that the excitation energy satisfies the threshold for polar optical scattering, phonon contribution is the dominant process in relaxing the system, otherwise, carrier-carrier mechanism is dominant. Furthermore, we present the temperature and pulse power dependent normalized luminescence intensity. The results are presented over a range of temperatures, electric field, and excitation energy of the laser pulse. For comparison, we also report the experimental time-resolved photoluminescence studies on GaN samples. There is a good agreement between the simulation and experiment in normalized luminescence intensity results. Therefore, we show that we can explain the dynamics of the photo-excited carriers in GaN by including only carrier-carrier and carrier-phonon interactions and a relatively simple two-band electronic structure model.

  2. Structural Characterization of Cubic GaN Grown on GaAs(001) Substrates

    ZHENG Xinhe; QU Bo; WANG Yutian; YANG Hui; LIANGJunwu; HAN Jingyi


    Structural characteristics of cubic GaN epilayers grown on GaAs(001) were studied using X-ray double-crystal diffraction technique. The structure factors of cubic GaN(002) and (004) components are approximately identical. However, the integrated intensities of the rocking curve for cubic (002) components are over five times as those of (004)components. The discrepancy has been interpreted in detail considering other factors. In the conventional double crystal rocking curve, the peak broadening includes such information caused by the orientation distribution (mosaicity) and the distribution of lattice spacing. These two kinds of distributions can be distinguished by the triple-axis diffraction in which an analyzer crystal is placed in front of the detector.Moreover, the peak broadening was analyzed by reciprocal lattice construction and Eward sphere. By using triple-axis diffraction of cubic (002) and (113)components, domain size and dislocation density were estimated. The fully relaxed lattice parameter of cubic GaN was determined to be about 0.451 ± 0.001nm.

  3. Basic Equations for the Modeling of Gallium Nitride (gan) High Electron Mobility Transistors (hemts)

    Freeman, Jon C.


    Gallium nitride (GaN) is a most promising wide band-gap semiconductor for use in high-power microwave devices. It has functioned at 320 C, and higher values are well within theoretical limits. By combining four devices, 20 W has been developed at X-band. GaN High Electron Mobility Transistors (HEMTs) are unique in that the two-dimensional electron gas (2DEG) is supported not by intentional doping, but instead by polarization charge developed at the interface between the bulk GaN region and the AlGaN epitaxial layer. The polarization charge is composed of two parts: spontaneous and piezoelectric. This behavior is unlike other semiconductors, and for that reason, no commercially available modeling software exists. The theme of this document is to develop a self-consistent approach to developing the pertinent equations to be solved. A Space Act Agreement, "Effects in AlGaN/GaN HEMT Semiconductors" with Silvaco Data Systems to implement this approach into their existing software for III-V semiconductors, is in place (summer of 2002).

  4. High-pressure crystallization of GaN for electronic applications

    Grzegory, I


    The results obtained with the use of pressure-grown GaN single-crystalline substrates allow us to draw the following conclusions important for the construction of In-free UV light emitting diodes and lasers and InGaN-based high-power blue lasers. (1) The application of pressure-grown GaN single-crystalline substrates allows us to grow near-dislocation-free layer structures by both metal- organic chemical vapour deposition and molecular beam epitaxy. (2) The elimination of dislocations leads to highly efficient UV emission from GaN and GaN/AlGaN quantum wells, which is impossible for strongly dislocated structures grown on sapphire. (3) At high excitations (e.g. in lasers), dislocations are also effective non-radiative recombination centres in InGaN-containing structures, so the elimination of these defects is crucial for better performance of blue lasers. In this paper, the optical and structural properties of the near-dislocation-free GaN-based structures leading to the above conclusions are discussed.

  5. Variable Energy Positron Annihilation Spectroscopy of GaN Grown on Sapphire Substrates with MOCVD

    HU Yi-Fan; C.D. Beling; S. Fung


    @@ Depth profiled Doppler broadening of positron annihilation spectroscopy (DBPAS), which is also called the variable energy positron annihilation spectroscopy (VEPAS), is used in characterization of GaN grown on sapphire substrates with metal-organic chemical vapour deposition (MOCVD). The GaN film and the film/substrate interface are investigated. The VEPFIT (variable energy positron fit) software was used for analysing the data,and the positron diffusion length of the sapphire is obtained. The results suggest that there is a highly defected region near the GaN/sapphire interface. This thin dislocated region is generated at the film/substrate interface to relieve the strain. Effects of implantation dose on defect formation, for the GaN/Sapphire samples, which implanted by Al+ ions, are also investigated. Studies on Al+ implanted GaN films (not including the interface and sapphire) have revealed that there are two different regions of implantation damage. For the low Al+ implantation dose samples, in the region close to the surface, defects are mainly composed of vacancy pairs with small amount of vacancy clusters, and in the interior region of the film the positron traps are vacancy clusters without micro-voids. For the highest dose sample, however, some positron trap centres are in the form of micro-voids in the second region.

  6. A new approach to grow C-doped GaN thick epitaxial layers

    Gogova, D.; Siche, D.; Albrecht, M.; Irmscher, K.; Rost, H.J.; Fornari, R. [Leibniz Institute for Crystal Growth, Max-Born-Strasse 2, 12489 Berlin (Germany); Rudko, G.Yu. [V. Lashkarev Institute of Semiconductors Physics, 03028 Kiev (Ukraine)


    In this study we employ a new method for growth of carbon-doped wurtzite crystalline GaN (GaN:C) based on vapour phase transport of Ga by the pseudohalide hydrogen cyanide HCN. GaN:C layers with a thicknesses from 10 to 100 {mu}m and up to 19 mm in size were grown from gallium melt and ammonia as feeding materials in a carbon-containing equipment. The properties of the GaN:C layers were characterized by low-temperature photoluminescence (LTPL), High-Resolution X-ray Diffraction (HRXRD), Secondary Ion Mass Spectrometry (SIMS) and room-temperature Hall effect and Raman spectroscopy measurements. HRXRD studies demonstrated good crystalline quality of the thick GaN layers (the Rocking curve FWHMs are 570 arcsec for the (0004) reflection and 561 arcsec for the (10-14) reflection for 10 {mu}m thick samples). The LTPL and Raman spectroscopy confirmed the good optical and structural quality of the material. The carbon concentration measured by SIMS was 6x10{sup 18} cm{sup -3}, however, the room-temperature Hall effect experiments showed n-type conductivity. Carbon acceptor incorporation into GaN (from the transport agent) as well as the reason of its electrical overcompensation by unintentional impurities like oxygen and silicon is discussed. Ways of technological process improvement are proposed. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Rare-earth defect pairs in GaN: LDA+U calculations

    Sanna, Simone; Schmidt, W. G.; Frauenheim, Th.; Gerstmann, U.


    The structural and electronic properties of rare-earth (RE) (Eu, Er, and Tm) related defect pairs in GaN have been investigated theoretically. Based on LDA+U total-energy calculations, their possible role in the luminescence process is discussed. In all charge states, the lanthanides show a strong preference for the Ga-lattice site, either as isolated substitutional or complexed with intrinsic defects. With respect to the electronic valence, a proper description of correlation effects of the strongly localized 4f electrons is shown to be crucial, especially if the REGa is paired with donors like the Ga interstitial or the N vacancy. The pairs formed by REGa substitutionals and vacancies or interstitials lower the symmetry and are found to locally distort the environment. By this, they are quite effective in relaxing the selection rules for the luminescent intra- 4f -shell transitions. While for n -type GaN, the next-nearest-neighbor pair REGaVGa pair is energetically favored, for p -type GaN, the REGaVN pair provides the most stable configuration and introduces shallow levels close to the conduction band, which can act as assistant levels in the luminescence process.

  8. Transmission electron microscopy of defects and internal fields in GaN structures

    Mokhtari, H


    segregation in the defects. In MBE grown GaN/In sub 0 sub . sub 1 Ga sub 0 sub . sub 9 N/GaN SQWs and MQWs, V shaped defects were found to be present in the InGaN regions, which locally reduced the width of the InGaN layers. The main aim of this study was to understand the microstructure of GaN and InGaN/GaN and to examine electric fields around the defects, and across the quantum wells by electron holography. For this reason different types of GaN and InGaN/GaN samples have been prepared and studied. Conventional transmission electron microscopy has been used for structural study of two MBE grown GaN/GaAs samples, grown at room temperature and at 340 deg C. The structure of the samples were found to be hexagonal polycrystalline in an amorphous GaN matrix, and textured hexagonal polycrystalline material respectively. The experimental results indicate that the higher growth temperature results in a more crystalline material with a higher density of bigger grain sizes. Different types of undoped and Si doped Ga...

  9. Polarity in GaN and ZnO: Theory, measurement, growth, and devices

    Zúñiga-Pérez, Jesús; Consonni, Vincent; Lymperakis, Liverios; Kong, Xiang; Trampert, Achim; Fernández-Garrido, Sergio; Brandt, Oliver; Renevier, Hubert; Keller, Stacia; Hestroffer, Karine; Wagner, Markus R.; Reparaz, Juan Sebastián; Akyol, Fatih; Rajan, Siddharth; Rennesson, Stéphanie; Palacios, Tomás; Feuillet, Guy


    The polar nature of the wurtzite crystalline structure of GaN and ZnO results in the existence of a spontaneous electric polarization within these materials and their associated alloys (Ga,Al,In)N and (Zn,Mg,Cd)O. The polarity has also important consequences on the stability of the different crystallographic surfaces, and this becomes especially important when considering epitaxial growth. Furthermore, the internal polarization fields may adversely affect the properties of optoelectronic devices but is also used as a potential advantage for advanced electronic devices. In this article, polarity-related issues in GaN and ZnO are reviewed, going from theoretical considerations to electronic and optoelectronic devices, through thin film, and nanostructure growth. The necessary theoretical background is first introduced and the stability of the cation and anion polarity surfaces is discussed. For assessing the polarity, one has to make use of specific characterization methods, which are described in detail. Subsequently, the nucleation and growth mechanisms of thin films and nanostructures, including nanowires, are presented, reviewing the specific growth conditions that allow controlling the polarity of such objects. Eventually, the demonstrated and/or expected effects of polarity on the properties and performances of optoelectronic and electronic devices are reported. The present review is intended to yield an in-depth view of some of the hot topics related to polarity in GaN and ZnO, a fast growing subject over the last decade.

  10. GaN nanowire arrays with nonpolar sidewalls for vertically integrated field-effect transistors

    Yu, Feng; Yao, Shengbo; Römer, Friedhard; Witzigmann, Bernd; Schimpke, Tilman; Strassburg, Martin; Bakin, Andrey; Schumacher, Hans Werner; Peiner, Erwin; Suryo Wasisto, Hutomo; Waag, Andreas


    Vertically aligned gallium nitride (GaN) nanowire (NW) arrays have attracted a lot of attention because of their potential for novel devices in the fields of optoelectronics and nanoelectronics. In this work, GaN NW arrays have been designed and fabricated by combining suitable nanomachining processes including dry and wet etching. After inductively coupled plasma dry reactive ion etching, the GaN NWs are subsequently treated in wet chemical etching using AZ400K developer (i.e., with an activation energy of 0.69 ± 0.02 eV and a Cr mask) to form hexagonal and smooth a-plane sidewalls. Etching experiments using potassium hydroxide (KOH) water solution reveal that the sidewall orientation preference depends on etchant concentration. A model concerning surface bonding configuration on crystallography facets has been proposed to understand the anisotropic wet etching mechanism. Finally, NW array-based vertical field-effect transistors with wrap-gated structure have been fabricated. A device composed of 99 NWs exhibits enhancement mode operation with a threshold voltage of 1.5 V, a superior electrostatic control, and a high current output of >10 mA, which prevail potential applications in next-generation power switches and high-temperature digital circuits.

  11. Transport, Growth Mechanisms, and Material Quality in GaN Epitaxial Lateral Overgrowth

    Baca, Albert G.; Bartram, M.E.; Coltrin, M.E.; Crawford, M.H.; Han, J.; Missert, N.; Willan, C.C.


    Growth kinetics, mechanisms, and material quality in GaN epitaxial lateral over-growth (ELO) were examined using a single mask of systematically varied patterns. A 2-D gas phase reaction/diffusion model describes how transport of the Ga precursor to the growth surface enhances the lateral rate in the early stages of growth. In agreement with SEM studies of truncated growth runs, the model also predicts the dramatic decrease in the lateral rate that occurs as GaN over-growth reduces the exposed area of the mask. At the point of convergence, a step-flow coalescence mechanism is observed to fill in the area between lateral growth-fronts. This alternative growth mode in which a secondary growth of GaN is nucleated along a single convergence line, may be responsible for producing smooth films observed to have uniform cathodoluminescence (CL) when using 1{micro}m nucleation zones. Although emission is comprised of both UV ({approximately}365nm) and yellow ({approximately}550nm) components, the spectra suggest these films have reduced concentrations of threading dislocations normally associated with non-radiative recombination centers and defects known to accompany growth-front convergence lines.

  12. Steps towards a GaN nanowire based light emitting diode and its integration with Si-MOS technology

    Limbach, Friederich


    This work is concerned with the realization and investigation of a light emitting diode (LED) structure within single GaN nanowires (NWs) and its integration with Si technology. To this end first a general understanding of the GaN NW growth is given. This is followed by investigations of the influence which doping species, such as Mg and Si, have on the growth of the NWs. The experience gathered in these studies set the basis for the synthesis of nominal p-i-n and n-i-p junctions in GaN NWs. Investigations of these structures resulted in the technologically important insight, that p-type doping with Mg is achieved best if it is done in the later NW growth stage. This implies that it is beneficial for a NW LED to place the p-type segment on the NW top. Another important component of an LED is the active zone where electron-hole recombination takes place. In the case of planar GaN LEDs, this is usually achieved by alloying Ga and In to form InGaN. In order to be able to control the growth under a variety of conditions, we investigate the growth of InGaN in the form of extended segments on top of GaN NWs, as well as multi quantum wells (MQWs) in GaN NWs. All the knowledge gained during these preliminary studies is harnessed to reach the overall goal: The realization of a GaN NW LED. Such structures are fabricated, investigated and processed into working LEDs. Finally, a report on the efforts of integrating III-nitride NW LEDs and Si based metaloxide-semiconductor field effect transistor (MOSFET) technology is given. This demonstrates the feasibility of the monolithic integration of both devices on the same wafer at the same time.

  13. My Favorite Day



    It’s Friday, November 14th. I’m happy today. In1 8 o’clock I have Chinese. I like it because it’s fun. Then I have math and art. In2 this day I can have P.E. in the afternoon. That’s my favorite subject. I play football and basketball. Then I have a two-days3 holiday. At 6 o’clock p.m. I can swimming4 for an hour. In5 Friday evening I have a party with my friends.

  14. Ferromagnetism in with Fe implanted GaN and TiO{sub 2}; Ferromagnetismus in mit Fe implantierten GaN und TiO{sub 2}

    Talut, Georg


    In the present study it was tried to create a diluted magnetic semiconductor on the basis of GaN and TiO{sub 2} by means of ion beam implantation. In most cases, by characterization of structural and magnetic properties, it was possible to prove that the ferromagnetic state is related to either spinodal decomposition or secondary phase formation. In case of Fe implanted GaN spinodal decomposition, epitaxially oriented {alpha}-Fe or {epsilon}-Fe{sub 3}N nanocrystals were found to be responsible for the ferromagnetic behavior. In addition, the formation of {gamma}-Fe clusters was observed. Similarly, in TiO{sub 2} the ferromagnetism is related to the formation of epitaxially oriented {alpha}-Fe clusters. Dependent on the process parameters during annealing experiments several various secondary phases were formed. A critical examination of the references in literature points out the significance of usage of sensitive and complementary probe techniques (like CEMS, SQUID, XRD, EXAFS), in order to be able to discuss the origin of ferromagnetism in the field of diluted magnetic semiconductors in a proper way. (orig.)

  15. Evaluation of deep levels in GaN grown by RF-MBE on GaN template by capacitance DLTS

    Mitsunaga, T.; Yagishita, Y.; Osaka, J.; Mizutani, T. [Department of Quantum Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya (Japan); Kurouchi, M. [Venture Business Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya (Japan); Kishimoto, S. [Department of Quantum Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya (Japan); Venture Business Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya (Japan)


    The dependence of deep levels in GaN epitaxial layer grown by molecular beam epitaxy on the V/III ratio was studied by capacitance deep level transient spectroscopy (DLTS). Four peaks corresponding to the electron traps were observed in the unintentionally n-doped GaN films grown at various growth conditions. The deep level concentrations of T1 (0.31 eV) and T4 (0.21 eV) traps increased with decrease of the V/III ratio. This suggests that T1 and T4 traps are related to the N-vacancies. Those of T2 (0.84 eV) and T3 (1.13 eV) traps did not show obvious dependence on the V/III ratio, but the concentration of the T2 and T3 traps increased with increase of the residual carrier concentration. T2 and T3 traps might have some correlation with the residual donor species. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Electric field dependence of optical phonon frequencies in wurtzite GaN observed in GaN high electron mobility transistors

    Bagnall, Kevin R.; Dreyer, Cyrus E.; Vanderbilt, David; Wang, Evelyn N.


    Due to the high dissipated power densities in gallium nitride (GaN) high electron mobility transistors (HEMTs), temperature measurement techniques with high spatial resolution, such as micro-Raman thermography, are critical for ensuring device reliability. However, accurately determining the temperature rise in the ON state of a transistor from shifts in the Raman peak positions requires careful decoupling of the simultaneous effects of temperature, stress, strain, and electric field on the optical phonon frequencies. Although it is well-known that the vertical electric field in the GaN epilayers can shift the Raman peak positions through the strain and/or stress induced by the inverse piezoelectric (IPE) effect, previous studies have not shown quantitative agreement between the strain and/or stress components derived from micro-Raman measurements and those predicted by electro-mechanical models. We attribute this discrepancy to the fact that previous studies have not considered the impact of the electric field on the optical phonon frequencies of wurtzite GaN apart from the IPE effect, which results from changes in the atomic coordinates within the crystal basis and in the electronic configuration. Using density functional theory, we calculated the zone center E2 (high), A1 (LO), and E2 (low) modes to shift by -1.39 cm-1/(MV/cm), 2.16 cm-1/(MV/cm), and -0.36 cm-1/(MV/cm), respectively, due to an electric field component along the c -axis, which are an order of magnitude larger than the shifts associated with the IPE effect. Then, we measured changes in the E2 (high) and A1 (LO) Raman peak positions with ≈1 μm spatial resolution in GaN HEMTs biased in the pinched OFF state and showed good agreement between the strain, stress, and electric field components derived from the measurements and our 3D electro-mechanical model. This study helps to explain the reason the pinched OFF state is a suitable reference for removing the contributions of the electric field and

  17. Electrical transport in GaN and InN nanowires; Elektrischer Transport in GaN- und InN-Nanodraehten

    Richter, Thomas Fabian


    This thesis discusses the analysis of the electrical transport in GaN and InN nanowires at room temperature and deep temperatures. From those measurements two different transport models for those two in matter of the band banding completely different materials have been found. In the investigation of the GaN nanowires the main focus was the electrical transport in dependence of the diameter and the n-doping. With the use of IV-measurements on those MBE grown nanowires with different diameters at dark and under UV illumination as well as the decay of the persistent photocurrent, it was possible to find an for GaN untypical behaviour. The electrical transport in those wires is extremely diameter dependent. The dark current shows space charged limited current. With the help of those cognitions a diameter dependent transport model could be found. The transport phenomena in those wires is based on the diameter depending band bending at the edge of the wires caused by the Fermi level pinning inside the forbidden band. This model can be fit to the data with the three parameter doping, fermi level pinning and wire diameter. On the base of those effects a method to determine the doping concentration inside those wires without field effect measurements and contact resistance has been developed. The defect structure inside those wires has been analysed with the help of spectral photoluminescence measurements. Here several defect bands have been found and it was possible with help of several contacts on one single wire to determine different defect regions along the wire and to explain them by the lattice mismatch between nanowire and substrate. Further temperature depending measurements and investigations on Schottky contacted wires as well as on GaN wires with AlN tunnel structures complete the work on GaN. The electrical characterisation on a large scale of undoped and doped InN nanowires shows linear growth of the dark current with the diameter up to wires of around 100 nm

  18. CERN openlab Open Day

    Purcell, Andrew Robert


    The CERN openlab Open Day took place on 10 June, 2015. This was the first in a series of annual events at which research and industrial teams from CERN openlab can present their projects, share achievements, and collect feedback from their user communities.

  19. Governing To‐day

    Turner, Kevin


    Governing To-day denotes a domain of research, and what the thesis undertakes is a theoretical discussion of some questions of method vis-à-vis researching this domain. There are two aspects to the title that enfold one another. Firstly, “governing to-day” signposts that it is to!day that is to b...... of departure in the research and writing of the French philosopher and historian, Michel Foucault. It is primarily within the writings of Foucault that the thesis seeks to find a workaround to the problem thrown forth by the aforementioned questions of method.......Governing To-day denotes a domain of research, and what the thesis undertakes is a theoretical discussion of some questions of method vis-à-vis researching this domain. There are two aspects to the title that enfold one another. Firstly, “governing to-day” signposts that it is to...... in time, in the present!day, in this time that is our own, and so forth, that forms the object of enquiry. Accordingly, “governing to!day” denotes both a government of the present and government in the present. In working through said questions of method, the thesis sketches out an approach that takes...

  20. 90-Day Cycle Handbook

    Park, Sandra; Takahashi, Sola


    90-Day Cycles are a disciplined and structured form of inquiry designed to produce and test knowledge syntheses, prototyped processes, or products in support of improvement work. With any type of activity, organizations inevitably encounter roadblocks to improving performance and outcomes. These barriers might include intractable problems at…