bluuebunny/crossref_metadata_2025_split huggingface dataset:
Time-resolved RHEED Studies of the Growth of Epitaxial ZnSe Films on GaAs by Pulsed Laser Deposition
Authors: McCamy James W. , Aziz Michael J. 
Published: April 2011

AbstractFilm growth consists of two basic processes, deposition and surface relaxation, with opposing effects on the evolution of surface roughness. The pulsed-laser deposition (PLD) growth process has the unique feature of having periods of very high deposition rates on μs time scales followed by periods, on the order of seconds, with only surface relaxation. In this paper we report the first efforts towards exploiting this unique feature to study these two basic processes independently. Thin epitaxial films of ZnSe were grown using PLD on (001) GaAs and 2° miscut (001) GaAs substrates. For growth on both the singular and vicinal surfaces, RHEED patterns taken following growth showed clear, streaky first zone and sharp second zone spots, and well-defined Kikuchi lines; these features are indicative of a smooth growth surface and high quality film. No reconstruction of the growth surface was observed, in contrast to behavior observed in molecular beam epitaxy. Time-resolved RHEED measurements show that a single morphology developed during growth on singular (001) GaAs. However, during growth on miscut (001) GaAs, two morphologies developed, one transitory and one appearing to evolve towards steady state. When growth on the miscut substrate was stopped, recovery of the RHEED signal was observed. The rate of recovery could be attributed to two relaxation processes, as differentiated by their time constants. Potential origins of these observations are discussed.
Radiochromic Thin-Film Sensor Using Blue Tetrazolium in Polyvinyl Alcohol
Authors: Hsu C.-K. , Al-Sheikhly M. , Mclaughlin W. L. , Christou A. 
Published: April 2011

AbstractA new radiochromic thin-film sensor using the blue tetrazolium chloride salt (BT) dissolved in polyvinyl alcohol (PVA) has been developed for deep ultraviolet, and gamma and xray dosimetry systems. The radiation-sensitive blue tetrazolium (BT2+), pale yellowish before irradiaton, registers a permanent purple high-resolution image upon irradiation. The distinctive coloration in terms of increase of optical density (net absorbance, ΔA) at 552 nm is measured spectrophotometrically and is proportional to the amount of radiation energy absorbed per unit mass (absorbed dose, D). The films have broad monitoring range, being able to detect radiation doses as low as 1 kGy and as high as 75 kGy. The radiochromic images show a gradual postirradiation increase in absorbance, especially during the first 24 hrs. There is also a small but predictable variation in sensitivity with temperature during irradiation. Furthermore, the responses to gamma radiation are found to be dependent on absorbed dose rate, but can be minimized by increasing the dye precursor concentration (BT2+).
Chemical Etching of AlN and InAlN in KOH Solutions
Authors: Vartuli C. B. , Lee J. W. , MacKenzie J. D. , Pearton S. J. , Abernathy C. R. , Zolper J. C. , Shul R. J. , Ren F. 
Published: April 2011

ABSTRACTWet chemical etching of A1N and InxAl1-xN was investigated in KOH-based solutions as a function of etch temperature, and material quality. The etch rates for both materials increased with increasing etch temperatures, which was varied from 20 °C to 80 °C. The crystal quality of A1N prepared by reactive sputtering was improved by rapid thermal annealing at temperatures to 1100 °C with a decreased wet etch rate of the material measured with increasing anneal temperature. The etch rate decreased approximately an order of magnitude at 80 °C etch temperature after a 1100 °C anneal. The etch rate for In0.19Al0.81N grown by Metal Organic Molecular Beam Epitaxy was approximately three times higher for material on Si than on GaAs. This corresponds to the superior crystalline quality of the material grown on GaAs. Etching of InxAl1-xN was also examined as a function of In composition. The etch rate initially increased as the In composition changed from 0 to 36%, and then decreased to 0 Å/min for InN. The activation energy for these etches is very low, 2.0 ± 0.5 kcal•mol-1 for the sputtered A1N. The activation energies for InAIN were dependent on In composition and were in the range 2–6 kcal mol-1. GaN and InN layers did not show any etching in KOH at temperatures up to 80 °C.
Photo-Assisted Anodic Etching of Gallium Nitride Grown by MOCVD
Authors: Lu Hongqiang , Wu Ziming , Bhat Ishwara 
Published: April 2011

ABSTRACTIn this paper, the first study of photo-assisted anodic etching of unintentionally doped n-GaN at room temperature is reported. The electrolyte used is a mixture of buffered aqueous solution of tartaric acid and ethylene glycol. The etching rate varies from ∼20 Å/min to as high as 1600 Å/min. A systematic study shows that i) the etch rate, as well as the surface roughness, increases with the current density; ii) the etching rate is the highest when the pH of the electrolyte is around 7; iii) the etching is faster when there is more ethylene glycol in the electrolyte solution.
Investigation of Aluminum and Titanium/Aluminum Contacts to n-Type Gallium Nitride
Authors: Luther B. P. , Mohney S. E. , Jackson T. N. , Asif Khan M. , Chen Q. , Yang J. W. 
Published: April 2011

ABSTRACTWe report on a study of Al and Ti/Al contacts to n-type GaN. Al contacts on n-GaN (7 x l017cm-3) annealed in forming gas at 600°C reached a minimum contact resistivity of 8x10~6Qcm2 and had much better thermal stability than reported by previous researchers. Ti/Al (35nm/l 15nm) contacts on n-GaN (5xl0I7cm~3) had resistivities of 7 x l0"6Qcm2 and 5xl0"6Qcm2 after annealing in Ar at 400°C for 5min and 600°C for 15sec, respectively. Depth profiles of Ti/Al contacts annealed at 400°C showed that low contact resistance was only achieved after Al diffused to the GaN interface. We propose that the mechanism for ohmic contact formation in Ti/Al contacts annealed in the 400-600°C range includes reduction of the native oxide on GaN by Ti and formation of an Al-Ti intermetallic phase in intimate contact with the GaN. Contacts with different Ti/Al layer thicknesses were investigated and those with 50nm/100nm layers had the same low resistance and better stability than 25nm/125nm contacts.
Optical and Electrical Characteristics of Single-Quantum-Well InGaN Light-Emitting Diodes
Authors: Perlin Piotr , Osiński Marek , Eliseev Petr G 
Published: April 2011

ABSTRACTWe have studied the electroluminescence and photoluminescence of Nichia single-quantum-well Al0.2Ga0.8N/In0.45Ga0.55N/GaN green light-emitting diodes over a broad range of temperatures (15-300 K) and currents (0.2 μA - 2 A). The most striking behavior is an anomalous temperature shift of both photo- and electroluminescence, with the emission peak moving towards higher energies with increasing temperature. This blue shift is opposite to that of the energy gap of the active layer, which practically excludes interband transitions as responsible for the observed optical transitions. We suggest that population effects within the band tails can account for the observed anomaly. We also determined that the current flowing through the p-n junction is dominated by carrier tunneling, the omnipresent effect in the GaN-based optoelectronic devices.
Stimulated Emission from Single- and Multiple-Quantum-Well GaN-AlGaN Separate-Confinement Heterostructures
Authors: Loeber D. A. S. , Anderson N. G. , Redwing J. M. , Flynn J. S. , Smith G. M. , Tischler M. A. 
Published: April 2011

ABSTRACTStimulated emission characteristics are examined for GaN-AlGaN separate-confinement quantum-well heterostructures grown by MOVPE on 4H-SiC substrates. We specifically focus on comparison of structures with different quantum well active region designs. Polarization resolved edge emission spectra and stimulated emission thresholds are obtained under optical pumping using a stripe excitation geometry. Stimulated emission characteristics are studied as a function of the number of quantum wells in the structure, and are correlated with surface photoluminescence properties. We find reduced stimulated emission thresholds and increased surface photoluminescence intensities as the number of quantum wells is reduced, with the best results obtained for a single-quantum-well structure. These results should provide useful information for the design of GaN-based quantum well lasers.
III-V Nitride Growth by Atmospheric-Pressure MOVPE with a Three-Layered Flow Channel
Authors: Uchida Kazuo , Tokunaga Hiroki , Inaishi Yoshiaki , Akutsu Nakao , Matsumoto Koh , Itoh Tsuyoshi , Egawa Takashi , Jimbo Takashi , Umeno Masayoshi 
Published: April 2011

ABSTRACTWe introduce III-V nitrides growth including GaN as well as InGaN by a newly developed atmospheric-pressure metal-organic vapor phase epitaxy system with a three layered flow channel which is a promising system for a large scale production. First, we have shown through computer simulation that a laminar flow of gases is maintained at 1000 °C in the three layered flow channel. Second, as a part of epitaxial results, we have found that the surface roughness of a low temperature-grown buffer layer on sapphire substrates, which can be measured by atomic force microscope, should be minimum in order to grow high quality GaN. We also report the growth of a double heterostructure of Ino. 15Gao.85N/GaN which shows a strong near band-edge emission in room temperature photoluminescence.
Kinetics of Nitrogen in GaAsN Layers During GaAs Overgrowth
Authors: Bandić Z. Z. , Hauenstein R. J. , O’Steen M. L. , McGill T. C. 
Published: April 2011

ABSTRACTA set of GaAsN/GaAs strained layer superlattices was grown on GaAs (001) substrates by electron cyclotron resonance microwave plasma assisted molecular beam epitaxy. An ex-situ high resolution X-ray diffraction was employed to characterize interface quality and determine the effective nitrogen content, as a function of growth temperature, of buried GaAsN layers. The interface quality, which was assessed through FWHM’s and intensities of superlattice peaks, and nitrogen content were found to change dramatically in the temperature range from 540°C to 580°C. A first order kinetic model was introduced to quantitatively explain this dependencies, in terms of energetically favorable N for As anion exchange and thermally activated N desorption and segregation processes. The strong nitrogen surface segregation process, which acts concurrently with nitrogen desorption is found to be responsible for both degradation of interface quality and reducing nitrogen content at elevated temperatures. The predicted nitrogen profile smearing of (2 – 3)nm, obtained from the model, is found to be in good agreement with cross-sectional transmission electron microscopy observations.
Doping Studies of n- and p-Type AlxGa1-xN Grown by ECR-Assisted MBE
Authors: Korakakis D. , Ng H. M. , Ludwig K. F. , Moustakas T. D. 
Published: April 2011

ABSTRACTAlxGal−xN films (x≤0.60) were grown on c-plane sapphire and (0001) 6H-SiC substrates using ECR plasma assisted Molecular Beam Epitaxy. Evidence of long range ordering in the investigated AlxGal−xN films is presented. Without intentional dopants the films are semi-insulating with resistivities ranging from 103 to 105 Ω.cm. The films were doped n-type with Si and p-type with Mg. The carrier concentration in the Si doped films, as determined by Hall effect measurements, was between 1016 to 1019 cm−3. At constant Si cell temperature, the carrier concentration was found to be reduced with AlN mole fraction, consistent with the observation that the donor ionization energy increases with Al content. Correspondingly, the electron mobility decreases with Al concentration, a result attributed to alloy scattering. The Mg doped films were found to exhibit p-type conductivity by thermoelectric power measurements with resistivities varying from 3 to 30 Ω-cm.
Large-Area Growth of InGaN/AlGaN Using In Situ Monitoring
Authors: Woelk E. , Schmitz D. , Strauch G. , Wachtendorf B. , Jorgensen H. 
Published: April 2011

ABSTRACTA newly developed Metalorganic Chemical Vapor Deposition (MOCVD) reactor for processing batches of seven 50mm wafers per run at deposition temperatures up to 1600°C is introduced. The substrates are individually rotated by means of gas bearings utilizing high purity gas for operation. In order to achieve the maximum uniformity on a wafer the uniformity of the growth temperature was maximized. Pyrometric measurements revealed a temperature uniformity across the susceptor of ±4°C at a temperature of 1300°C. Growth of GaN and GaInN produced uniform layers regarding composition and thickness. On a 50mm diameter wafer the standard deviation for the thickness of a GaN layer is 6% and the standard deviation for the composition of a GaInN layer as determined by photoluminescence is 2%.
The Growth of GaN Films by Migration-Enhanced Epitaxy
Authors: Hooper S. E. , Foxon C. T. , Cheng T. S. , Jeffs N. J. , Ren G. B. , Lacklison D. E. , Orton J. W. , Duggan G. 
Published: April 2011

ABSTRACTGallium Nitride epitaxial films were grown by migration enhanced epitaxy directly on sapphire (0001) without using any pre-growth substrate nitridation or low temperature buffer layers. In comparison with our material grown directly on sapphire by conventional molecular beam epitaxy, a significant improvement in the surface morphology and layer properties, measured by reflection high energy electron diffraction, X-ray diffraction, scanning electron microscopy, room temperature photoluminescence and the Hall effect, was observed for material grown by migration enhanced epitaxy.
Gallium Nitride Thick Layers: Epitaxial Growth and Separation from Substrates
Authors: Bel’kov V. V. , Botnaryuk V. M. , Fedorov L. M. , Diakonu I. I. , Krivolapchyuk V. V. , Scheglov M. P. , Zhilyaev Yu. V. 
Published: April 2011

ABSTRACTWe investigated the possibilities of vapour phase epitaxy in an open tube chloride system for thick GaN film deposition on sapphire substrates. The methodes of the buffer layer deposition were proposed and developed. The methods of fast ( up to 100 microns / hour ) was developed. Parameters of good quality gallium nitride epitaxy were obtained.To determine the quality of fast grown epitaxial layers we used X-ray diffraction and photoluminescence measurements. The halfwidth of the rocking curve for the best samples was equal to 4-6 minutes. Luminescense spectrum ( T=77K ) had a maximum near 3.46 eV. A signal in the visible wavelength range was hardly observed. Polished layers were transparent.A special initial treatment of the substrates allowed us to separate thick ( up to 300 micron ) epitaxial gallium nitride layers from sapphire. It was shown that it is possible to use separated films for homoepitaxy of GaN.
Surface Energy Constraints for Heteroepitaxial Growth on Compliant Substrates: Morphology of GaN Grown on Sc Layers
Authors: Koleske D. D. , Wickenden A. E. , Freitas J. A. , Kaplan R. , Prokes S. M. 
Published: April 2011

ABSTRACTAn empirical relationship linking surface energy to bulk modulus is presented which suggests that the thermodynamic growth mode for heteroepitaxy on compliant substrates should be 3-D. As an example of this behavior, GaN growth on Sc is shown for various growth conditions. 2-D growth is obtained when the GaN is grown on top of a low temperature GaN nucleation layer. Our results indicate that surface and interface energies, in addition to, lattice matching and thermal matching play an important role in determining the heteroexpitaxial growth morphology of GaN. There appears to be no net reduction in the dislocation density for GaN films grown on the Sc layers, because the GaN film has to be grown on a low temperature nucleation layer.
ZnO Buffer Formed on Si and Sapphire Substrates for GaN MOVPE
Authors: Shirasawa T. , Honda T. , Koyama F. , Iga K. 
Published: April 2011

ABSTRACTZnO layers have been deposited by electron beam (EB) evaporation and laser ablation molecular beam epitaxy (MBE) as buffer layers to grow GaN by metal organic vapor phase epitaxy (MOVPE). The photoluminescence spectrum of the ZnO layer deposited by an EB evaporator shows an emission peaks of 367 nm. GaN was grown on ZnO/Si, Si and sapphire substrates under the same growth condition employing low-temperature-grown AIN buffers to prevent the dissociation of ZnO during the high GaN growth. The GaN on ZnO/Si shows sharp photoluminescence spectra at room temperature and 10 K. These results indicate a potential use of ZnO/Si substrates for GaN based blue-UV optical devices such as vertical-cavity surface-emitting lasers (VCSELs).
MBE Growth and Characterization of Zns/Gan Heterostructures
Authors: Piquette E. C. , Bandić Z. Z. , McCaldin J. O. , McGill T. C. 
Published: April 2011

ABSTRACTHeterostructures involving ZnS/GaN show promise for the injection of holes from p-GaN into n-ZnS. This combination could result in multi-color electroluminescent displays. We have grown single crystal ZnS on GaN and sapphire (0001) by MBE using elemental sources. The ZnS was grown at temperatures from 150°C–400°C, with beam flux equivalent pressures of (0.3 – 2.0) × 10−7 torr. Growth rates of up to 0.4 μm per hour were observed for the lower growth temperatures, with rapidly diminishing rates for temperatures above 350μC. The GaN substrate consisted of a 3 μm epilayer grown on sapphire by MOCVD. XPS analysis revealed the presence of carbon surface contamination on the GaN, which was removed by in situ exposure to an RF nitrogen plasma. RHEED observations indicate that the zincblende ZnS layers commonly contain (111) twins, although twin free films may be grown at a high substrate temperature. The samples were characterized using photoluminescence and X-ray diffraction. X-ray peaks typically had FWHM of 400 arcsec for ω/2θ scans, and somewhat worse for ω scans. Photoluminescence spectra of the ZnS films doped with Ag and Al demonstrated the well known blue donor acceptor transition at 440 nm.
STM Observation of Nitrided-Ga on Si
Authors: Nakada Y. , Miwa S. , Okumura H. 
Published: April 2011

ABSTRACTTo investigate of the initial stage of GaN growth on Si, 0.2 Ga monolayers (ML) on Si (111) was nitrided and then the nitrided surfaces were observed by scanning tunneling microscopy (STM). An aggregation of islands whose longest edges had a direction rotated 15 ° from Si [110] direction was observed. The shape of islands looked like a pentagon. Surface roughness was estimated for several nitrided conditions. It was found that surface roughness becomes larger as the nitridation process proceeds.
Studies of Group III-Nitride Growth on Silicon
Authors: Blant AV , Cheng TS , Foxon CT , Bussey JC , Novikov SV , Tret’yakov VV 
Published: April 2011

ABSTRACTThe growth of Group III-Nitrides on Si substrates offers the possibility of combining optoelectronics with Si technology. We have been studying the growth of Group III-Nitrides on clean and oxidised Si surfaces with a view to local area epitaxy. X-ray data indicates that alloys of (AlGa)N and (InGa)N of controlled composition can be grown on Si using a plasma enhanced Molecular Beam Epitaxy method over the entire composition range from InN to AlN. Films grown on uncleaned, oxidised surfaces of Si are polycrystalline/amorphous in contrast to growth on chemically cleaned Si substrates which show the usual columnar structure common in Group III-Nitrides. XPS studies indicate that there is little tendency for spinodal decomposition, but the In peaks in (InGa)N alloys show that more than one chemical environment is present. The composition of the alloys deduced from electron probe microanalysis studies agree well with those from X-ray measurements, assuming Vegard’s law is valid for both alloy systems.
Photoconducting Properties of Ultraviolet Detectors Based on GaN and Al1-xGaxN Films Grown by ECR-MBE
Authors: Misra M. , Korakakis D. , Singh R. , Sampath A. , Moustakas T. D. 
Published: April 2011

ABSTRACTGaN and All-xGaxN films were grown by the method of ECR-MBE. Absorption constants as a function of wavelength were determined from transmission measurements. Photoconducting detectors were fabricated from these films and characterized in terms of their spectral response and photoconductive gain. Mobility-lifetime products were determined from the measurement of photoconductive gain. The resistivity and mobility-lifetime products of the films were varied from 10-109 ohm-cm and 10-3 -10-8 cm2/V respectively by changing the microwave power in the ECR discharge from 20-60 watts. The change in the mobility-lifetime product is attributed to change in the lifetimes of the photogenerated carriers. This assumption is supported by direct measurement of detector response times. Finally, we report for the first time, the detection of alpha particles using GaN detectors.
Dislocation Luminescence in Wurtzite GaN
Authors: Shreter Y. G. , Rebane Y. T. , Davis T. J. , Barnard J. , Darbyshire M. , Steeds J. W. , Perry W. G. , Bremser M. D. , Davis R. F. 
Published: April 2011

ABSTRACTThe 364 nm PL-system in GaN is attributed to the formation of dislocation excitons and charged dislocation excitons on c-axis screw dislocations. The binding energy for the dislocation exciton, charged dislocation exciton and a hole on the screw dislocation were determined as 35 meV, 7 meV and 65 meV respectively, in accord with experiment.
Photoluminescence Excitation Studies of the Optical Transitions in GaN
Authors: Kovalev D. , Averboukh B. , Meyer B. K. , Volm D. , Amano H. , Akasaki I. 
Published: April 2011

ABSTRACTWe present a detailed photoluminescence excitation study of the optical transitions in GaN. This technique is employed to distinguish between band-to-band excitation and exciton contribution to the formation of the free exciton, bound exciton, violet and yellow photoluminescence bands. We show the dominant role of the Fröhlich polar intraband scattering in the formation of the free exciton states. We demonstrate that bound exciton states in a large extent are created by the capture of the free excitons by shallow impurities as well as by phononassisted resonant excitation of the bound exciton states. The capture of the free carriers excited in the band continuum is a main excitation source for the violet and yellow bands. However, distinct A- and C-exciton resonances are detected in the excitation spectra of the violet and yellow emission bands.
Structure, Electronic Properties, and Defects of GaN Using a Self-Consistent Molecular-Dynamics Method
Authors: Stumm Petra , Drabold D. A. 
Published: April 2011

ABSTRACTMolecular dynamics simulations are employed to study defects in GaN. We use local basis density functional theory within the local density approximation where charge transfer between the ions is included in an approximate fashion. We find good agreement for the band structure of wurtzite and zincblende GaN compared to other recent calculations, suggesting the suitability of our method to describe GaN. A 96 atom GaN supercell is used to study the relaxations and electronic properties of common defects in the crystal structure, including Ga and N vacancies and antisites. We analyze the electronic signatures of these defects.