bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ni/Si-Based Ohmic Contacts to p- and n-Type GaN
Authors: Kamińska E. , Piotrowska A. , Barcz A. , Guziewicz M. , Kasjaniuk S. , Bremser M. D. , Davis R. F. , Dynowska E. , Kwiatkowski S. 
Published: April 2011

AbstractNi/Si-based ohmic contact scheme for GaN, based on the solid-phase regrowth (SPR) mechanism have been developed. Using Mg and Si as dopant species, ohmic contacts with a resistivity of ∼1*10-3Ωcm2 to p-GaN (p≈3*1017 cm-3) and n-GaN (n≈2*1017cm-3), respectively, have been obtained. SIMS, XRD, and RBS analysis show in as-deposited contacts, an initial reaction at GaN/Ni interface, leading to the formation of an Ni-Ga-N layer. The ohmic behavior of contacts, observed after annealing at 400°C, is accompanied by structural transformations in the contact region: i) the decomposition of Ni-Ga-N layer and ii) the growth of NiSi compound.
Metal Contacts to n- AlXGa1-xN
Authors: Sampath A. , Ng H. M. , Korakakis D. , Moustakas T. D. 
Published: April 2011

AbstractIn this paper we report on the formation of ohmic contacts to n- AlxGa1-xN alloys. The films were produced by plasma-assisted MBE and doped n- type with silicon at doping levels between 1018 to 1019 cm-3. Contacts were formed by sequential deposition of 200 Å of Ti and 2000 Å of Al and the contact resistivities were determined from TLM measurements. For low Al- content (x<. 10) the I-V characteristics are linear with contact resistivities of between 10-4 to 10-5 cm2. The contacts become progressively non-ohmic at Al concentrations greater than 10%. There results are consistent with the Schottky limit being applicable to these alloys and thus the Ti/Al contact forms Schottky barriers with higher barrier height as the conduction band of the alloy moves towards the vacuum level.
Status of Nitride Based Light Emitting and Laser Diodes on SiC
Authors: Doverspike K. , Bulman G. E. , Sheppard S. T. , Kong H. S. , Leonard M. , Dieringer H. , Weeks T. W. , Edmond J. , Brown J. D. , Swindle J. T. , Schetzina J. F. , Song Y- K , Kuball M. , Nurmikko A. 
Published: April 2011

AbstractSingle crystal thin films with compositions from the A1N-InN-GaN system were grown via metal-organic chemical vapor deposition (MOCVD) on single crystal 6H-SiC substrates. Blue light emitting (LED) and laser diode (LD) structures were fabricated. The conducting buffer layer LEDs employed an AlGaN buffer layer which provides a conduction path between SiC and the active device region. The external quantum efficiency of the LEDs was 3% at 20 mA- 3.6V and peak emission wavelength of 430 nm. Violet and blue LDs were fabricated and consisted of an 8-well InGaN/GaN multiple quantum well (MQW) active region in a separate confinement heterostructure (SCH) design. Lasing was obtained both on structures using an insulating buffer layer, and also on structures using a conducting buffer layer. The resulting lasers operated at room temperature using pulsed and continuous wave operation with an emission wavelength of 404-435 rim. The lowest threshold current density obtained for lasing was 11 kA/cm2.
The First Nitride Laser Diode on Silicon Carbide
Authors: Brown J. D. , Swindell J. T. , Johnson M. A. L. , Yu Zhonghai , Schetzina J. F. , Bulman G. E. , Doverspike K. , Sheppard S. T. , Weeks T. W. , Leonard M. , Kong H. S. , Dieringer H. , Carter C. , Edmond J. A. 
Published: April 2011

AbstractThis paper reports the events at NCSU leading up to and including those of June 5, 1997 which produced the first demonstration of a nitride laser diode on silicon carbide – and the very first nitride laser demonstration outside of Japan. All of the laser diode samples tested at NCSU were designed, grown, and fabricated into cleaved cavity test structures at Cree Research. Laser testing at NCSU consisted of spectral emission versus current measurements, light output power versus current (L-I) measurement, and light output polarization measurements versus current. The first successful laser on silicon carbide emitted at 402.6 nm. Subsequently, lasers displaying outputs ranging from 402.6 to 430.2 have been successfully tested at NCSU.
InGaN Laser Diodes Grown on SiC Substrate Using Low-Pressure Metal-Organic Vapor Phase Epitaxy
Authors: Kuramata A. , Domen K. , Soejima R. , Horino K. , Kubota S. , Tanahashi T. 
Published: April 2011

AbstractWe report the crystal growth and the characteristics of InGaN multiple quantum well (MQW) laser diodes grown on a 6H-SiC substrate using a low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). We discuss the buffer layer, the control of InGaN and AlGaN alloy composition, the magnesium doping of GaN and AlGaN, and the characteristics of the MQW structure. We also demonstrate the room-temperature pulsed operation of the laser diode. The threshold voltage was reduced to 15 V by improving the p-contact resistance. The threshold current was reduced to 500 mA by changing the MQW structure and employing high reflection coating.
A Kinetic Model for GaN Growth
Authors: Koleske D. D. , Wickenden A. E. , Henry R. L. , Desisto W. J. , Gorman R. J. 
Published: April 2011

AbstractA kinetic model is presented to explain GaN growth. The model is based on established values for the N and Ga desorption kinetics and well founded assumptions on the adsorption and decomposition of the N and Ga containing precursors. When grown on similar nucleation layers, it is shown that high quality GaN films are achieved when the V/III ratio is chosen to be slightly larger than the Ga and N desorption rates. The model is verified by comparing the structural, optical, and electrical properties of the GaN to the growth temperature and V/III ratio. The model explains several features of GaN growth including, growth conditions for smooth surface morphology, growth conditions for highly resistive GaN, and a possible explanation for the origin of Ga and N vacancies in GaN. Based on the growth model, ordering of the GaN during growth is achieved via an adsorption/desorption cycle where Ga and N containing species are exchanged between the gas phase boundary layer and the solid surface. Consequences of the model on establishing growth conditions and run-to-run reproducability are also discussed.
The Effect of Growth Temperature On The Microstructure of Movpe AlN/Si (111)
Authors: Zhou Mei , Perkins N. R. , Rehder E. , Kuech T. F. , Babcock S. E. 
Published: April 2011

AbstractThe epitaxy, defect structure, and heterointerface microstructure of MOVPE-grown AlN on <111> oriented Si were studied by transmission electron microscopy (TEM) in an investigation of the affects of the growth temperature (925°C–1 175°C) on the microstructure of low thickness (∼0.2 μm) films. A film grown at 1175°C was single crystalline with the following orientation relationship: (0001)AlN||(111)Si, <1120> and <1010>AlN||<211>Si. All AlN films grown at temperatures below 1100°C were wire-textured polycrystals with (0001)AlNlargely parallel to (111)siand some in-plane preferred orientation similar to that of 1175°C AlN epifilms. Columnar grains/domains with faceted top surfaces were observed for the entire growth temperature range. The mean column diameters decreased from 50 nm to 35 nm as the growth temperature decreased. The columnar grain/domain structure and the faceted tops resulted in peakto-valley surface roughness on the order of 20 nm. Sharp interfaces of AlN/Si were generally observed in all AIN films studied by HREM except for the 1075°C film where a transitional layer of approximately 15Å thick was observed at some interface regions. Defects typically encountered in large lattice mismatched heteroepitaxial systems were observed.
Bulk Gan Crystal With Low Defect Density Grown By Hydride Vapor Phase Epitaxy
Authors: Usui A. 
Published: April 2011

AbstractA new approach to grow thick GaN layers by hydride vapor phase epitaxy (HVPE) is described. Selective growth is carried out at the beginning of growth. The coalescence of selectively grown facet structures makes it possible to achieve a flat surface over the entire substrate. As a result, crack-free GaN films with mirror-like surfaces are successfully grown even to a thickness of about 100 μm on a 2-inch-diameter sapphire substrate. The extended defect density is as low as 6×107 cm−2. The reduction mechanism for dislocation is discussed based on TEM observation. The high optical properties of FIELO GaN are confirmed by 5 K photoluminescence and reflectance measurements.
MOCVD Growth of GaN on bulk AlN Substrates
Authors: Lu Hong-Qiang , Bhat Ishwara B. , Lee Byung-Chan , Slack Glen A. , Schowalter Leo J. 
Published: April 2011

AbstractIn this paper, the growth of epitaxial GaN layers on c-plane and a-plane bulk AIN substrates by metalorganic vapor phase epitaxy is reported. The AlN boules were grown by the sublimationrecondensation technique. Single crystal GaN films grown on the c-plane orientation replicate the substrate orientation. However the surface of the epilayer had a high density of cross-hatch defect lines, presumably caused by mechanical polishing damage. The low temperature PL spectra of these films were dominated by exciton emission at 3.470 eV with a FWHM of 14 meV at 7 K. On the other hand, GaN grown on the a-plane orientation AlN was polycrystalline and the surface was rough with ridge-like facets. The PL from this film showed a dominate peak at 3.406 eV which may originate from defect-bound excitons. The quality of the GaN layers grown on these AIN bulk substrates appeared to be limited by the surface preparation method, which has not been optimized.
Atomic Scale Aluminum and Strain Distribution in a Gan/AlxGa1−XN Heterostructure
Authors: Kisielowski Christian , Schmidt Olaf , Yang Jinwei 
Published: April 2011

AbstractA GaN/AlxGalxN multi-quantum well test structure with Al concentrations 0 ≤ xAl ≤ 1 was utilized to investigate the growth of AlxGal–xN barrier layers deposited by metal organic chemical vapor deposition (MOCVD). A transition from a two dimensional (2D) to a three dimensional (3D) growth mode was observed in AlxGa1–xN barriers with XAl ≥ 0.75. It is argued that the transition occurs because of growth at temperatures that are low compared with the materials melting points Tmelt. The resulting rough AlxGa1–xN surfaces can be planarized by overgrowth with GaN. Quantitative high resolution electron microscopy (HREM) was applied to measure composition and strain profiles across the GaN/AlxGa1−xN stacks at an atomic level. The measurements reveal a substantial variation of lattice constants at the AlxGa1−xN/GaN interfaces that is attributed to an Al accumulation.
A Combined Tem/Rheed, Sem/Cl Study Of Epitaxial Gan
Authors: Brown P. D. , Tricker D. M. , Xin Y. , Chengt T. S. , Foxont C. T. , Evanst D. , Galloway S. A. , Brock J. , Humphreys C. J. 
Published: April 2011

AbstractEpitaxial GaN grown by MBE has been characterised using the combined techniques of scanning electron microscopy / cathodoluminescence, reflection high energy electron diffraction (RHEED), and conventional transmission electron microscopy. Variations in spatial and spectral distributions of luminescence can arise due to embedded cubic inclusions within the hexagonal GaN matrix. The strong effect of doping on the crystallinity of the GaN deposit is illustrated, as determined by RHEED in a TEM.
Comparative Study of Typical Defects in III-Nitride Thin Films and Their Alloys
Authors: Dovidenko K. , Oktyabrsky S. , Narayan J. , Joshkin V. , Razeghi M. 
Published: April 2011

AbstractThe microstructure and typical defects in GaN and GaN/GaAlN thin film heterostructures grown on (0001)α-A12O3 were investigated using different transmission electron microscopy (TEM) techniques including diffraction contrast analysis, multiple dark field imaging, and highresolution TEM. The films were grown by metal-organic chemical vapor deposition (MOCVD) technique. All of the films exhibited good electrical/optical properties. Yet, films were found to be of two distinctive types in terms of the microstructure. Films of the first type (A) were found to contain high, up to the 109 cm2, density of inversion domains (IDs) as well as pure edge (b=l/3[11 20]), screw and mixed type dislocations with the average density of 109 - 1010 cm−2. Smoother surface of the film, absence of IDs, and low (down to 107 cm−2 in the device quality layers) density of screw and mixed type dislocations were found to be characteristic for the second type (B) microstructure. The majority of defects present in these B-type GaN and GaN/GaA1N thin films were found to be threading pure edge dislocations associated with low angle tilt sub-grain boundaries. Despite the 1010 cm−2 density of the edge dislocations, the films displayed the devicequality electrical characteristics. Type A and type B microstructure can be obtained by the variation of growth conditions. The correlation between the optical and structural properties are discussed.
Dislocation Distribution and Subgrain Structure of GaN Films Deposited on Sapphire by HVPE and MOVPE
Authors: Dunn K. A. , Babcock S. E. , Vaudo R. , Phanse V. , Redwing J. 
Published: April 2011

AbstractTransmission electron microscopy (TEM) was used to characterize the microstructure in GaN films deposited by two different methods. An 11 μm thick film was deposited directly on a sapphire substrate by HVPE; an 8 μm thick film was deposited on a 15 nm buffer layer of AIN on sapphire by MOVPE. The dislocation densities in the top layer of the HVPE and MOVPE ilms were ∼109 cm-2 and ∼5 x 109 cm-2 respectively. In the HVPE film this was almost exclusively threading dislocations (TDs), ∼70% of which had edge character. In addition to the TDs, the MOVPE sample also contained an appreciable number of dislocations lying in the basal plane. The microstructure of each film was dominated by a subgrain structure of slightly misoriented cells. In the MOVPE specimen, approximately 90% of the TDs were associated with subgrain walls, whereas only approximately 75% of the dislocations in the HVPE specimen were associated with walls. Both the HVPE and MOVPE samples experienced 40% coarsening of the cells through the thickness of the film. The subgrains of the MOVPE sample were 75% smaller than those in the HVPE sample (350 and 1300 nm, respectively). The average dislocation spacing in the walls was 50% smaller in the MOVPE sample than in the HVPE sample (82 and 180 nm, respectively).
Comparative Analysis of Strain and Stress in MBE and MOCVD grown GaN thin films on sapphire
Authors: Krüger Joachim , G.S. Sudhir , Corlatan Dorina , Cho Yonah , Kim Viihwan , Klockenbrink Ralf , Rouvimov Sergei , Liliental-Weber Zuzanna , Kisielowski Christian , Rubin Michael , Weber Eicke R. , McDermott Brian , Pittman R. , Gertner Edward R. 
Published: April 2011

AbstractIn this study, the causes of biaxial and hydrostatic stress components in epitaxially grown thin GaN films on sapphire are analyzed. It is observed that growth by Molecular Beam Epitaxy (MBE) and by Metal Organic Chemical Vapor Deposition (MOCVD) are governed by very similar physical principles. Differences in the absolute stress values are mainly due to the difference in growth temperature. It is argued that in the case of MOCVD growth the onset of plasticity for higher growth temperatures is responsible for a larger stress relaxation in the buffer layer. It is further found that either process can result in highly off-stoichiometric GaN layers, as manifested by the large variations in the a and c lattice parameters caused by intrinsic point defects.
The core Structure Of Pure Edge Threading Dislocations In Gan Layers Grown On [0001] SiC Or Sapphire By Mbe
Authors: Ruterana P. , Potin V. , Nouet G. 
Published: April 2011

AbstractThe best layers of GaN grown on SiC or sapphire contain high densities of threading dislocations, which do not seem to exhibit a critically important electrical activity. It is possible that the electrical activity of these dislocations may change with time. The large majority of the threading dislocations are a type, with 1/3 <1120> Burgers vector and their line parallel to the [0001] growth direction. The atomic structure of the a threading dislocations was found to correspond to 5/7 or 8 atoms rings core with rather equal frequency. The 8 atoms ring cores contain dangling bonds and will present favourable sites for atomic impurities which eventuallly can modify the good performances of the devices.
Structural Properties of Nitrides Grown by Omvpe on Sapphire Substrate
Authors: Amano H. , Takeuchi T. , Yamaguchi S. , Nitta S. , Kariya M. , Iwaya M. , Wetzel C. , Akasaki I. 
Published: April 2011

AbstractCrystalline quality of nitrides on sapphire by OMVPE has been investigated. First, in-situ observations of the crystallization process of the low temperature deposited AIN buffer layer or GaN buffer layer on sapphire substrate have been performed. Small hexagonal mesas were formed from the sapphire to the surface and finally they formed a stacked structure. Secondly, a low temperature deposited buffer layer located between the high temperature grown GaN was found to reduce the etch pit density of GaN films. Thirdly, structural properties of Ga1−xInxN (0 ≤x≤0.21, and x= l) on GaN and GaInN/GaN MQWs on GaN have been characterized by Xray diffraction. Coherently grown GaInN showed almost the same twisting as the underlying GaN layer, while free standing InN showed large twisting. Thickness of the well layers in MQWs has been controlled within one monolayer preciseness, and the fluctuation of alloy composition has been controlled to within 2%
Raman Analysis Of AlxGa1-xN Films
Authors: Bergman Leah , Dutta Mitra , Bremser Michael D. , Nam Ok-Hyun , Perry William G. , Alexon Dimitri , Davis Robert F. , Balkas Cengiz M. , Nemanich Robert J. 
Published: April 2011

AbstractRaman analysis of the E2 mode of AlxGal-xN in the composition range 0 ≤ x ≤ 1 is presented. The lineshape was observed to exhibit a significant asymmetry and broadening toward the high energy range. The spatial correlation model is discussed, and is shown to account for the lineshape. The model calculations also indicate the lack of a long-range order in the CVD (chemical vapor deposition) alloys. These results were confirmed by X-ray scattering: the relative intensity of the superlattice line was found to be negligible. The line broadening of the E2 mode was found to exhibit a maximum at a composition x∼0.5 indicative of a random disordered alloy system. The stress state of the alloys was found to be tensile and was attributed to the difference in the thermal expansion coefficients of the SiC substrate and the film.
Nondestructive, Room Temperature Determination Of The Nature Of The Band-Bending (Carrier Type) In Group III Nitrides Using Contactless Electroreflectance And Surface Photovoltage Spectroscopy
Authors: Krystek Wojciech , Pollak Fred H. , Feng Z. C. , Schurman M. , Stall R. A. 
Published: April 2011

AbstractUsing contactless electroreflectance and surface photovoltage spectroscopy at room temperature we have nondestructively evaluated the band bending (carrier type) at the surface of epitaxial n- and p-type GaN/sapphire samples as well as at both the InGaN surface and the GaN at the InGaN/GaN interface of samples of epitaxial InGaN grown on top of thick GaN epilayers/sapphire, having average n- and p-type character.
Localized Excitons in InGaN
Authors: ChichiBu S. , Deguchi T. , Sota T. , Wada K. , Nakamura S. 
Published: April 2011

AbstractEmission mechanisms of the device-quality quantum well (QW) structure and bulk three dimensional (3D) InGaN materials grown on sapphire substrates without any epitaxial lateral overgrown GaN (ELOG) base layers were investigated. The InxGx1−xN layers showed various degree of spatial potential (bandgap) fluctuation, which is probably due to a compositional inhomogeneity or monolayer thickness fluctuation produced by some kinetic driving forces initiated by the threading dislocations (TDs) or growth steps during the growth. The degree of fluctuation changed remarkably around nominal InN molar fraction x=0.2, which changes to nearly 8–10 % for the strained InxGa1−xN. This potential fluctuation induces energy tail states both in QW and 3D InGaN, showing a large Stokes-like shift combined with the red shift due to quantum confined Stark effect (QCSE) induced by the piezoelectric field. The spontaneous emission from undoped InGaN single quantum well (SQW) light-emitting diodes (LED's), undoped 3D double heterostructure (DH) LED's, and multiple quantum well (MQW) laser diode (LD) wafers was assigned as being due to the recombination of excitons localized at the potential minima, whose area was determined by cathodoluminescence (CL) mapping to vary from less than 60 nm to 300 nm in lateral size in the case of QW's. The lasing mechanisms of the cw In0.15Gao.85N MQW LD's having small potential fluctuation, whose bandgap broadenings are less than about 50 meV, can be described by the well-known electron-hole-plasma (EIHP) picture with Coulomb enhancement. The inhomogenous MQW LD's are considered to lase by EHP in segmented QW's or Q-disks. It is desirable to use entire QW planes with small potential inhomogeneity as gain media for higher performance LD operation.
Cathodoluminescence Studies of InGaN Quantum Wells
Authors: Ponce F. A. , Galloway S. A. , Goetz W. , Kern R. S. 
Published: April 2011

AbstractLow temperature cathodoluminescence has been used to investigate the spatial characteristics of light emission in InxGa1−xN single quantum wells. High spatial resolution, narrow band pass imaging shows the luminescence to be strongly inhomogeneous in wavelength as well as in intensity on a sub-micron scale. Cathodoluminescence spectra correlate favorably with photoluminescence spectra. However, when spectra are recorded from different areas in spot mode, the quantum emission varies significantly in wavelength. The observed variations are consistent with composition inhomogeneities in the quantum well.
Surface Characterization of GaN Formation on GaAs(100) Using Ammonia
Authors: Huh Chul , Ahn Sook , Han Jeong Yeul , Cho Keum Jae , Seo Jae Myung , Park Seong-Ju 
Published: April 2011

AbstractThe GaN formation on GaAs(100) using NH3 has been investigated using synchrotron radiation photoemission spectroscopy and an atomic force microscope (AFM). This study showed the effect of nitridation temperature on the compositional change, the chemical states, and the surface morphological changes in the nitridated surface layer. It was observed that ammonia is decomposed to an activated nitrogen atom above 700°C forming GaN on the surface. A thermally nitridated layer was composed of metallic Ga and GaN islands elongated along the [011] direction to relax the tensile strain in the [011] direction. As the nitridation temperature increased, the composition of GaN increased in the nitridated layer due to the efficient thermal decomposition of NH3 and the subsequent incorporation of the N atom to the metallic Ga. The surface morphology of the nitridated layer was also sensitive to the nitridation temperature and a smooth surface morphology could be obtained on the surface nitridated at 700°C.