bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-Resolution X-Ray Diffraction Analysis of “Devicequality” Cubic GaN Grown on (001)GaAs Substrate Prepared by Atomic-Hydrogen Treatment At “High Temperatures”
Authors: Yoshikawa A. , Qin Z. X. , Nagano H. , Sugure Y. , Jia A. W. , Kobayashi M. , Shimotomai M. , Kato Y. , Takahashi K. 
Published: April 2011

AbstractCubic GaN (c-GaN) layers were grown by if-plasma source MBE on (001) GaAs prepared by atomic-hydrogen treatment at “high temperatures”, and the structural properties of the epilayers were investigated by the high-resolution X-ray rocking curve and the reciprocal space mapping measurements. The growth temperature was varied from 620 to 740°C. It was found that single domain “device-quality” c-GaN layers could be grown for the first time; the FWHM of the X-ray rocking curves for the (002) c-GaN could be as small as 70 - 90 arcsec and the inclusion of h-GaN phase in the c-GaN epilayers grown at temperatures above 680°C could be less than 4×10-3.
Interactions of LO Phonons with Bound Excitons in Homoepitaxial GaN
Authors: Koron K. P. , Wysmolek A. , Baranowskil J. M. , Pakul K. , Bergman J. P. , Monemar B. , Grzegory I. , Porowski S. 
Published: April 2011

AbstractPhotoluminescence connected with excitons and their phonon replicas in undoped homoepitaxial MOCVD grown GaN layers have been studied in the temperature range 2 - 100 K. It is shown that the coupling between LO phonons and neutral acceptor bound excitons (ABE) is much stronger than the coupling between LO phonons and neutral donor bound excitons (DBE). In spite that emission due the DBE no-phonon is one order of magnitude stronger than the ABE one, the predominant feature of the first LO phonon replica of the excitonic structures is related to the ABE. It is argued that this fact is connected with delocalization of the acceptor wavefunction in the k-space which leads to a higher number of interacting LO phonons in the first replica. On the other hand, the second LO phonon replica of the excitonic structures is predominantly connected with the DBE. In the case of two LO phonons interacting with bound excitons the k - conservation has not so direct influence. In addition, the temperature dependence of LO phonon replicas and their kinetics in ps regime are also reported.
Effects of Piezoelectric Fields in GaInN/GaN and GaN/AlGaN Heterostructures and Quantum Wells
Authors: Im Jin Seo , Kollmer H. , Off J. , Sohmer A. , Scholz F. , Hangleiter A. 
Published: April 2011

AbstractThe effects of piezoelectric fields on the static and dynamic optical properties of GaInN/GaN and GaN/AIGaN double heterostructures and single quantum wells are studied by time-resolved photoluminescence. We find a strong increase of the luminescence decay time of the dominating transition with well thickness by several orders of magnitude. For well thicknesses larger than about 5 nm, two emission lines with strongly differing decay times are observed, which are attributed to spatially direct and indirect transitions. Our experimental findings are consistently explained by a quantitative model based on the piezoelectric fields in strained wurtzite quantum wells.
Photocurrent Response In Mg-Doped GaN
Authors: Qiu C. H. , Pankove J. I , Akasaki I. , Amano H. 
Published: April 2011

AbstractThe photoconductivity response of Mg-doped GaN thin films was studied in the time domain of 50 nanoseconds to a few milliseconds in the temperature range of 100K to 390K. The response time, defined as the time when the photocurrent decreased to half its maximum value, is in the sub-microseconds at room temperature, but increased to a few microseconds at low temperatures. The contact capacitance is suspected for this behavior. Slower decay components due to trapping at defect states were also observed.
Characterization Of Si-Doped GaN on (00.1) Sapphire Grown by MOCVD
Authors: Kim Chang Soo , Lee Dong-Kun , Lee Cheul-Ro , Now Sam Kyu , Lee In-Hwan , Bae In-Ho 
Published: April 2011

AbstractWe investigated structural, electrical and optical properties and their relationships for MOCVD grown Si-doped GaN with different doping levels. The changes in structural properties such as strain, crystallinity and strain relaxation as a function of carrier concentrations were measured by high-resolution triple-axis X-ray diffraction and reciprocal space mapping technique. As the carrier concentration of the samples increases from 1.6×1018 to 9.5×1018/cm3 Hall mobility decreases from 222 to 170cm2/Vsec, and peak intensity ratio of band edge to yellow luminescence in photoluminescence spectra decreases too. The variation of mosaic spread along [00.1] direction determined from full width at half maximum(FWHM) of GaN (00.2) peaks shows good agreement with the variation in Hall mobility. In addition, dislocation density determined from FWHM of (10.2) peaks is shown to be related to the variation in the intensity of yellow luminescence in PL spectra.
Substrate Surface Treatments and “Controlled Contamination” in GaN / Sapphire MOCVD
Authors: Golan Yuval , Fini Paul , Denbaars Steven P. , Speck James S. 
Published: April 2011

AbstractWe have used atomic force microscopy (AFM) to study the effect of common substrate surface treatments for the metal-organic chemical vapor deposition (MOCVD) of GaN on sapphire. It appears that contaminants play a major role in the surface chemistry and strongly influence the morphology of the treated surfaces. In order to investigate the role of these contaminants, we have introduced the concept of “controlled contamination” (CC), namely, exposure of the sapphire surfaces to controlled amounts of potential contaminants in-situ and investigation of the resulting sapphire morphology. The results showed that sapphire, considered to be a very stable oxide surface, is clearly reactive in the GaN MOCVD chemical environment at the high temperatures (HT) employed, allowing us to use CC for obtaining sapphire substrates with controlled roughness. Nevertheless, epitaxial growth using the two-step GaN MOCVD process appears to be very robust and practically insensitive to the (submicronscale) substrate morphology.
The Doping and Characterization of Erbium-Implanted Gan
Authors: Torvik J. T. , Feuerstein R. J. , Qiu C. H. , Pankove J. I. , Namavar F. 
Published: April 2011

AbstractStrong room temperature Er-related photoluminescence (PL) and electroluminescence (EL) at 1539 nm was observed from Er and 0 implanted n-type GaN. Good device performance requires that the Er-related excitation and emission processes be efficient. Single exponential PL and EL time decays with l/e lifetimes of 2.33 ms and 1.74 ms indicates highly efficient radiative process. The Er excitation process in GaN was studied by comparing the efficiency of direct Erabsorption, electron-hole pair recombination, and hot electron (impact) excitation. The strongest Er luminescence and the lowest pump power was found using impact excitation.
Evidence of Potential Fluctuations in Modulation Doped GaN/AlGaN Heterostructures
Authors: Buyanov A. V. , Sandberg J. , Bergman J. P. , Sernelius B. E. , Holtz P-O , Monemar B. , Amano H. , Akasaki I. 
Published: April 2011

AbstractWe report on novel transport and optical data for GaN/AlGaN modulation doped heterostructures grown by Metal Organic Chemical Vapor Deposition (MOCVD). Variable temperature galvanomagnetic, resistivity, photoluminescence and photoconductivity measurements have been performed. Evidence for potential fluctuations is provided by the observation of weakly localized transport at low temperatures, together with a negative magnetoresistance due to disorder in the interface region. Additional evidence for a built-in electric field caused by the fluctuations near the heterointerface region is given by the observation of photoconductivity dips resonant with free excitons, indicating free exciton ionization. It is concluded that interface roughness, dislocations, and similar structural defects, have a strong influence on the transport properties of the two-dimensional electron gas in these structures.
Local Electronic Structure Of Defects In Gan From Spatially Resolved Electron Energy-Loss Spectroscopy
Authors: Natusch M. K. H. , Botton G. A. , Broom R. F. , Brown P. D. , Tricker D. M. , Humphreys C. J. 
Published: April 2011

AbstractThe optical properties and their modification by crystal defects of wurtzite GaN are investigated using spatially resolved electron energy-loss spectroscopy (EELS) in a dedicated ultra-high vacuum field emission gun scanning transmission electron microscope. The calculated density of states of the bulk crystal reproduces well the features of the measured spectra. The profound effect of a prismatic stacking fault on the local electronic structure is shown by the spatial variation of the optical properties derived from low-loss spectra. It is found that a defect state at the fault appears to bind 1.5 electrons per atom.
Theoretical Investigation Of Extended Defects In Group-III Nitrides
Authors: Wright A. F. 
Published: April 2011

AbstractWe have investigated two types of extended defects commonly found in AIN, GaN and InN films using density-functional techniques. First, basal-plane stacking faults have been studied for all three compounds. Stacking-fault energies were found to be largest in AIN and smallest in GaN consistent with density-functional results for their wurtzite/zinc-blende energy differences. In addition, the 4H and 6H structures were found to have lower energies than zinc blende for all three compounds. Second, we have investigated the electronic structure and formation energy for an edge dislocation in AIN. The full-core dislocation structure was found to have a filled electronic level approximately 0.55 eV above the valence-band edge and an empty level 1.4 eV below the conduction-band edge. An open-core structure was found to have filled and empty electronic levels closer to the middle of the energy gap. Formation energies for these two geometries suggest that the full-core structure would be expected to form in p-type material whereas both are expected in n-type material.
Velocity Overshoot And Ballistic Electron Transport In Wurtzite Indium Nitride
Authors: Foutz B. E. , O'leary S. K. , Shur M. S. , Eastman L. F. , Bhapkar U. V. 
Published: April 2011

AbstractUsing an ensemble Monte Carlo approach, ballistic transport and velocity overshoot effects are examined in InN and compared with those in GaN and GaAs. It is found that the peak overshoot velocity is in general greater than both GaN and GaAs. Furthermore, the velocity overshoot in InN occurs over distances in excess of 0.4 μm, which is comparable to GaAs but is significantly longer than the overshoot in GaN. These strong overshoot effects, combined with a high peak drift velocity, large low-field mobility, and large saturation drift velocity, should allow InN based field effect transistors to outperform their GaN and GaAs based counterparts.
Theory of Interfaces and Surfaces of Wide-Gap Nitrides
Authors: Rapcewicz Krzysztof , Nardelli Marco Buongiorno , Bungaro Claudia , Briggs E. L. , Bernholc J 
Published: April 2011

AbstractThe results of extensive theoretical studies of the properties of interfaces and surfaces of the wide-gap III-V nitride semiconductors are reviewed. The phenomena that we have investigated include band offsets and transport properties in nitride-based devices, surface reconstruction energetics and adsorbate-substrate interactions. In the modelling of realistic blue-laser multiquantum well structures such as In0.2Ga0.8N/In1−xGaxN (x > 0.8) superlattices, pyro- and piezo-electric effects are found to be strong enough to reduce the interband recombination rate and limit the efficiency of an actual device. We have also studied the influence of growth conditions and surface polarity upon the morphology of (0001) GaN surfaces, which are the primary growth faces. The charge transfer between the Ga and N atoms in GaN and the very large electronegativity of nitrogen are found to play decisive roles in determining the stable reconstructions. The behavior of Mg at the Ga-terminated (0001) surface has also been investigated. We find that Mg in the Gasubstitutional site is preferred to adatom sites on the surface. Further, our results suggest that Mg prefers to segregate to the surface.
Band Offsets In GaN/AlN and AlN/SiC Heterojunctions
Authors: Binggeli Nadia , Ferrara Philippe , Baldereschi Alfonso 
Published: April 2011

AbstractWe have investigated the structural trends of the band offsets in GaN/AlN and AlN/SiC heterojunctions using the ab initio pseudopotential method. In the zincblende GaN/AlN (100), (110), and (111) heterojunctions, the band offsets are relatively insensitive to interface orientation. Bulk strain effects, however, can modify the offset by as much as 0.4 eV in coherently strained AlN/GaN and GaN/AlN (100) junctions. The band alignment in the heterovalent AlN/SiC (110) and (111) heterojunctions depends on the geometry and stoichiometry of the interface. Valence band offsets as high as 2.5 eV are obtained for neutral AlN/SiC(11) junctions with a mixed Al/Si interface layer and as low as 1.3 eV with a mixed N/C layer. Atomic relaxation plays a major role in determining the offset. The change from zincblende (111) to wurtzite (0001) crystal structure in GaN/AlN and AlN/SiC heterojunctions selectively affects the conduction band offset, and has only a minor influence on the valence discontinuity.
Valence Band Parameters for Wurtzite GaN and InN
Authors: Yeo Y. C. , Chong T. C. , Li M. F. 
Published: April 2011

AbstractTheoretical studies and design of quantum well lasers employing InGaN require material parameters for both GaN and InN. However, the Luttinger-like effective-mass parameters for InN are currently unavailable. In this work, we extract effective-mass parameters for wurtzite GaN and InN from their electronic band structures calculated using the Empirical Pseudopotential Method (EPM). We obtain the electron and hole (including the heavy- (HH), light- (LH), and crystal-field split-off (CH) holes) effective-masses at the Γ point in the kz and the in-plane kx-ky plane) directions using a parabolic fit. In addition, the hole effective-mass parameters are derived using the 6×6 effective-mass Hamiltonian and the k.p method. Our results will be useful for material design in wide-gap nitride-based semiconductor lasers containing InGaN.
Doping, Activation of Impurities, and Defect Annihilation in Gan by High Pressure Annealing
Authors: Suski T. , Jun J. , Leszczynski M. , Teisseyre H. , Grzegory I. , Porowski S. , Baranowski J. M. , Rocket A. , Strite S. , Stonert A. , Turos A. , Tan H. H. , Swilliams J. , Jagadish C. 
Published: April 2011

AbstractGaN semiconductor is characterized by strong bonding and high vapor pressure of nitrogen. The strong bonds limit an efficiency of annealing procedures required for variety of semiconductor technologies, for example, post-implantation annealing, or doping by diffussion. Maximum temperatures employed up to now (at ambient pressure) in GaN annealing have not exceeded about 1100°C. A desired increase of annealing temperatures would cause a decomposition of GaN unless an elevated pressure of N2 is supplied. In this work, we report onapplication of high pressure annealing procedures (temperatures up to 1550°C and pressures up to 16 kbar) which enabled us to study variation of the properties of epitaxial films and bulk crystal of GaN. In particular, we discuss the following results obtained using high pressure annealing: i) structural quality improvement and increase of the thermal strain in as grown epitaxial layers of GaN/A12O3, The annealing at above 1300°C resulted in the decrease of the X-ray rocking curve width from about 700 arc sec. down to 470 arc sec., ii) drastic increase of bandedge (bound exciton) photoluminescence intensity iii) enhancement in removal of implant damage, iv) increase of diffusivity of Zn and Mg atoms (introduced by implantation and/or diffusion from external source). For Zn in epitaxial layers of GaN/A12O3 a diffusion starts at 1200–1250°C, v) enhancement of the blue-photoluminescence intensity in Zn and Mg implanted GaN. The performed experiments give an evidence of the importance of the defect (dislocations) in diffusion of Zn and Mg in the GaN semiconductor.
In-Situ Observation Of Aln Formation During Nitridation Of Sapphire By Ultrahigh Vacuum Transmission Electron Microscopy
Authors: Yeadon M. , Marshall M. T. , Hamdani F. , Pekin S. , Morkoc H. , Gibson J. M. 
Published: April 2011

AbstractUsing a novel ultrahigh vacuum transmission electron microscope (UHV TEM) with insitu molecular beam epitaxy capability we have studied the nitridation of (0001) sapphire upon exposure to ammonia. Atomically flat sapphire surfaces for the experiments were obtained by high temperature annealing. Subsequent exposure to ammonia flow at 950°C led to the successful synthesis of epitaxial AIN; the films were characterized in-situ using TEM. Complimentary ex-situ atomic force microscopy (AFM) was also performed in order to characterize the surface morphology before and after nitridation.The experiments indicate that AIN grows by a 3D island growth mechanism. Electron diffraction patterns suggest an abrupt AIN/sapphire interface with no evidence of the formation of Al–O–N compounds. The rate limiting step in the nitridation reaction appears to be the diffusion of nitrogen and oxygen species between the free surface of the growing AIN film and the reaction interface. It is inferred from kinetic measurements that diffusion of these species occurs along the boundaries between coalescing AIN islands.
A Technique For Rapid Thick Film Sic Epitaxial Growth
Authors: Khlebnikov I. , Sudarshan T. S. , Madangarli V. , Capano M. A. 
Published: April 2011

AbstractIn this paper we demonstrate the growth of thick SiC epitaxial layers (≥100 μm) of good structural quality at a high growth rate (>100 μm/hr) by controlling the vapor dynamics during conventional physical vapor transport (PVT) process. We propose that our PVT technique be used to ‘repair’ or ‘heal’ commercially available substrates dominated by micropipes, by ‘filling up’ the micropipes through crystal growth inside the micropipe. Extensive experiments performed on thick SiC epitaxial layers grown on Lely substrates indicate that the thick epitaxial layers are of single polytype of high structural quality, with a single peak X-ray rocking curve of less than 12 arcsecs FWHM.
Metallization Of Thin Graphite Layers After Cs Deposition On 4H-Sic(0001) Surfaces
Authors: Nienhaus H. , Elsbergen V. Van 
Published: April 2011

AbstractThe interaction of cesium atoms with graphitized 4H-SiC(0001) surfaces was investigated by use of Auger electron, ultraviolet photoemission and high-resolution electron energy-loss spectroscopy (HREELS) as well as work function measurements with a Kelvin probe. The samples were annealed at temperatures well above 1300 K resulting in a formation of about two graphite layers on top of the SiC substrates. The corresponding low-energy electron diffraction image shows a () pattern. Cs deposition on graphitized SiC occurs in two subsequent stages. First, even small amounts of evaporated Cs lead to a spontaneous decrease in work function by 1.8 eV. The work function stays constant after further evaporation corresponding to an intercalation of Cs into the graphite overlayer. In the second stage Cs atoms are adsorbed on top of the Cs-intercalated compound resulting in a further decrease of work function. The graphite layer is effectively metallized by Cs evaporation. This is confirmed by a Fermi edge which is observed in the photoemission spectra even after the smallest dose applied. Moreover, the excitation of optical Fuchs-Kliewer phonons in SiC by HREELS is significantly quenched by the metallic overlayer and the electron energy-loss spectra exhibit features which are typical for thin homogeneous metal layers on surfaces of heteropolar semiconductors.
Pld Epitaxial Tin And Pt Ohmic Metallizations To P-Type 6H-Sic Using Focused Ion Beam Surface Modification
Authors: Iliadis A. A. , Andronescu S. N. , Edinger K. , Orloff J. H. , Talyansky V. , Vispute R. D. , Sharma R. P. , Venkatesan T. , Wood M. C. , Jones K. A. 
Published: April 2011

AbstractThe development of low resistance ohmic metallizations to p-type 6H-SiC using a novel approach of focused ion beam (FIB) surface-modification and ex-situ epitaxial pulsed laser deposition (PLD) of TiN and Pt without further annealing, is reported. The FIB(Ga) surfacemodification and ex-situ epitaxial TiN and Pt PLD metallizations showed a significant reduction in contact resistance with surface-modification, reaching a minimum contact resistance value of 4.4×10−5 Ohm cm2 for the TiN system at an ion dose of 5.0×1016 ions/cm 2 and energy of 20 KeV. This contact resistance value is one of the lowest values reported to date. The Pt system showed increased contact resistance values as compared with the TiN, and reached minimum values for lower ion doses. The contact resistance values reported here are comparable to or lower than those reported for conventionally deposited and annealed contacts to p-type SiC.
Single Crystal Silicon Carbide On Silicon Using A Supersonic Gas Jet Of Methylsilane
Authors: Ustin S. A. , Long C. , Lauhon L. , Ho W. 
Published: April 2011

AbstractCubic SiC films have been grown on Si(001) and Si(111) substrates at temperatures between 600 °C and 900 °C with a single supersonic molecular beam source. Methylsilane (H3SiCH3) was used as the sole precursor with hydrogen and nitrogen as seeding gases. Optical reflectance was used to monitor in situ growth rate and macroscopic roughness. The growth rate of SiC was found to depend strongly on substrate orientation, methylsilane kinetic energy, and growth temperature. Growth rates were 1.5 to 2 times greater on Si(111) than on Si(001). The maximum growth rates achieved were 0.63 μm/hr on Si(111) and 0.375μm/hr on Si(001). Transmission electron diffraction (TED) and x-ray diffraction (XRD) were used for structural characterization. In-plane azimuthal (ø-) scans show that films on Si(001) have the correct 4-fold symmetry and that films on Si(111) have a 6-fold symmetry. The 6-fold symmetry indicates that stacking has occurred in two different sequences and double positioning boundaries have been formed. The minimum rocking curve width for SiC on Si(001) and Si(111) is 1.2°. Fourier Transform Infrared (FTIR) absorption was performed to discern the chemical bonding. Cross Sectional Transmission Electron Microscopy (XTEM) was used to image the SiC/Si interface.
Epitaxial Growth Of High Quality Sic By Sublimation Close Space Technique
Authors: Nishino S. , Yoshida T. , Nishio Y. 
Published: April 2011

AbstractSemiconducting SiC is expected for power devices and higher breakdown voltage of the device is required. Growth rate of epilayer by conventional CVD is about 3 μ m/h. To make a thick epilayer, more than 10 hours are needed. To minimize the growth time, we propose sublimation epitaxial method by close space technique (CST). In the CST, source ( polycrystalline 3C–SiC plate) and substrate is closely separated by spacer and source material is sublimed and transferred to the substrate in argon. Epitaxial layers with specular surface were obtained on 6H–SiC substrates at a substrate temperature around 2200 °C and growth rate was about 100 μ/h. Nitrogen-bound exciton was observed by PL measurement at 2 K in the epilayer when 3C–SiC plate with high purity was employed as the source material. Crystallinity of the epilayer was characterized by Raman spectroscopy.