bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical properties of GaN with Ga and N polarity
Authors: Reshchikov M. A. , Huang D. , Yun F. , Visconti P. , King T. , Morkoç H. , Jasinski J. , Liliental-Weber Z. 
Published: April 2011

AbstractWe compared photoluminescence (PL) and cross-sectional transmission electron microscopy (TEM) characteristics of GaN samples with Ga and N polarities grown by molecular beam epitaxy (MBE) on sapphire substrates. Ga-polar films grown at low temperature typically have very smooth surfaces, which are extremely difficult to etch with acids or bases. In contrast, the N-polar films have rougher surfaces and can be easily etched in hot H3PO4 or KOH. The quality of the X-ray diffraction spectra is also much better in case of Ga-polar films. Surprisingly, PL efficiency is always much higher in the N-polar GaN, yet the features and shape of the PL spectra are comparable for both polarities. We concluded that, despite the excellent quality of the surface, MBE-grown Ga-polar GaN layers contain higher concentration of nonradiative defects. From the analyses of cross-sectional TEM investigations, we have found that Ga-polar films have high density of threading dislocations (5x109 cm-2) and low density of inversion domains (1x107 cm-2). For N-polar GaN the situation is the reverse: the density of dislocations and inversion domains are 5x108 and ~1x1011 cm-2, respectively. One of the important conclusions derived from the combined PL and TEM study is that inversion domains do not seem to affect the radiative efficiency very adversly, whereas dislocations reduce it significantly.
Growth of High Al Concentration AlGaN for Solar Blind Photodetector Applications
Authors: Guo Shiping , Pophristic Milan , Ferguson Ian , Peres Boris , Lamarre Phil , Tobin Steve , Wong Kwok , Reine Marion , Sood Ashok 
Published: April 2011

AbstractThe development of a metalorganic chemical vapor deposition growth process for AlxGa1-xN materials with high aluminum composition (x∼0.40-0.60) on sapphire substrates is reported. Room temperature Hall measurements of Si-doped AlGaN epilayers with x∼0.40 show a narrow window for efficient doping with a carrier concentration of ∼1.5x1018 cm-3 and a mobility of ∼35 cm2/V-s obtained under optimum growth conditions. AlxGa1-xN-based solar-blind p-i-n device structures were grown and diode I-V curves were obtained with a high R0A of <2.9×1010 ohm-cm2. Secondary ion mass spectroscopy measurements show a sharp transition between regions of high concentration of Mg (2×1020 cm-3) and Si (1×1019 cm-3) in p-GaN and n-AlGaN layers, respectively.
Fast Proton Damage Effects on the Luminescence Properties of High-Quality GaN
Authors: Yang Qing , Feick Henning , Armitage Rob , Weber Eicke R. 
Published: April 2011

AbstractHigh-quality GaN layers grown by hydride-vapor phase epitaxy (HVPE) and homoepitaxial layers grown thereon by molecular beam epitaxy (MBE) are studied after fast proton irradiation. A radiation-induced decrease of the band edge luminescence is observed. Time-resolved photoluminescence (PL) reveals a significant reduction of the carrier lifetime. A lifetime degradation constant of Kt = 4×10-15cm2/ns is reported for very thick HVPE GaN, and large variations are observed for the different layers. Partial recovery of the carrier lifetime and PL intensity with annealing is observed for thin HVPE GaN but not for the MBE overgrowth layer.
Effects of the Schottky electrode structure in GaN based UV-VUV (50-360 nm) photodetector
Authors: Motogaito Atsushi , Ohta Keiichi , Hiramatsu Kazumasa , Ohuchi Youichiro , Tadatomo Kazuyuki , Hamamura Yutaka , Fukui Kazutoshi 
Published: April 2011

AbstractCharacterization of Schottky barrier UV detectors with a comb-shaped electrode and a transparent electrode for VUV region using synchrotron radiation was carried out. These Schottky type detectors are effective to operate in UV and VUV light (50<l >360 nm). In particular, the latter realizes high responsivity (0.01 A/W for VUV light) and no photoemission of Au and GaN. The penetration depth for VUV light was estimated to 0.01 m. So the VUV light was absorbed in near the surface of i-GaN layer or the interface of Au and i-GaN layer.
Electrical Characterization of GaN Metal Oxide Semiconductor Diode using Sc2O3 as the Gate Oxide
Authors: Mehandru R. , Gila B.P. , Kim J. , Johnson J.W. , Lee K.P. , Luo B. , Onstine A.H. , Abernathy C. R. , Pearton S.J. , Ren F. 
Published: April 2011

AbstractGaN metal oxide semiconductor diodes were demonstrated utilizing Sc2O3 as the gate oxide. Sc2O3 was grown at 100°C on MOCVD grown n-GaN layers in a molecular beam epitaxy (MBE) system, using a scandium elemental source and an Electron Cyclotron Resonance (ECR) oxygen plasma. Ar/Cl2 based discharges was used to remove Sc2O3, in order to expose the underlying n-GaN for ohmic metal deposition in an Inductively Coupled Plasma system. Electron beam deposited Ti/Al/Pt/Au and Pt/Au were utilized as ohmic and gate metallizations, respectively. An interface trap density of 5 × 1011 eV-1cm-2was obtained with the Terman method. Conductance-voltage measurements were also used to estimate the interface trap density and a slightly higher number was obtained as compared to the Terman method. Results of capacitance measurements at elevated temperature (up to 300°C) indicated the presence of deep states near the interface.
Transparent ZnO-Based Ohmic Contact to p-GaN
Authors: Kaminska E. , Piotrowska A. , Golaszewska K. , Guziewicz M. , Kruszka R. , Kudla A. , Ochalski T. , Barcz A. , Dietl T. , Matsukura F. , Sawicki M. , Wawro A. , Zielinski M. , Jasinski J. , Liliental-Weber Z. 
Published: April 2011

AbstractHighly conductive ZnO films were fabricated on p-GaN in a two-step process. First, zinc was thermally evaporated on p-GaN. Next, zinc film was oxidized in oxygen flow. To increase the conductivity of ZnO, nitrogen was introduced into zinc during its deposition. The above procedure proved successful in fabricating ZnO of the resistivity of ~1x10-3Ωcm and resulted in ohmic contacts of resistivity ~1x10-2Ωcm2 to low-doped p-GaN, and light transmittance of ~75% in the wavelength range of 400-700 nm.
Photoluminescence of Zn-doped GaN grown by HVPE
Authors: Reshchikov M. A. , Huang D. , Morkoç H. , Molnar R. J. 
Published: April 2011

AbstractWe investigated the behavior of photoluminescence (PL) in a wide range of temperatures and excitation intensities from Zn-doped GaN grown on c-plane of sapphire by hydride vapor phase epitaxy (HVPE). The low-temperature PL spectrum exhibited sharp peaks in the excitonic part with the full width at half maximum (FWHM) of about 5 meV. The peaks were attributed to free excitons and excitons bound to shallow donors and to Zn-related acceptors. A blue band with a maximum at 2.9 eV and FWHM of 0.33 eV dominated in the PL spectrum at low temperatures. We observed a significant UV shift (about 50 meV) of this band when the excitation density was increased from 10-6 to 100 W/cm2 or when the temperature of the sample was increased from 15 to 300 K. With increasing temperature, the blue band intensity quenched by 104 times in the range 180 - 250 K with the activation energy of about 0.64 eV. When the sample was illuminated from the substrate side, the blue band intensity dropped only 30 times in the temperature range of 180 - 340 K, and the activation energy did not exceed 0.25 eV. The PL spectrum of the GaN:Zn samples under investigation also contained broad red and green bands with maxima at about 1.8 and 2.4 eV, respectively. In PL from the substrate side, the blue and yellow (2.2 eV) luminescence dominated in the defect-related region of PL spectrum. Time-resolved PL measurements revealed nonexponential decay of the defect-related bands.
Raman Studies on Oxygen Doped GaN Grown by Molecular Beam Epitaxy
Authors: Papadimitriou D. , Ptak A.J. , Korakakis D. , Giles N.C. , Myers T.H. 
Published: April 2011

AbstractHigh quality Ga-polarity GaN films were grown by plasma-assisted molecular beam epitaxy to study strain effects due to oxygen incorporation. Oxygen concentrations up to 2 × 1022 cm-3 were studied. Layers containing oxygen at levels above 1022 cm-3 exhibit severe cracking while oxygen concentrations less than 1021 cm-3 apparently does not introduce significant strain. Raman spectra of O2-doped films were evaluated with respect to spectra of unintentionally doped GaN films (n=4x1014 cm-3) grown under the same conditions except for the O2-flux. Analysis of the E2 (high frequency phonon mode near 570 cm-1) Raman band indicated the heaviest doped samples exhibit compressive strain. Frequency-shifts between 0.7 and 0.9 cm-1 were observed as a function of the distance from the crack edges in the heavily doped samples, implying a strain (da/a) of the order of 5x10-4.
Optical Properties of Carbon Doped Cubic GaN Epilayers Grown on GaAs (001) Substrate by Molecular Beam Epitaxy
Authors: As D. J. , Köhler U. , Lischka K. 
Published: April 2011

AbstractThe optical properties of Carbon doped cubic GaN epilayers have been investigated by temperature and intensity dependent photoluminescence measurements. RF-plasma assisted molecular beam epitaxy equipped with an e-beam-evaporation source for carbon doping is used to grow the cubic GaN layers on GaAs (001) substrates. With increasing Carbon flux a new photoluminescence line at 3.08 eV appeared at 2K. This line is attributed to a donor acceptor transistion, which involves the shallow CN acceptor. From the spectral position the binding energy of the C acceptor is estimated to be about EC = 0.215 eV. Our experiments demonstrate that C indeed introduces a shallow acceptor in cubic GaN with an acceptor binding energy, which is about 15 meV lower than that observed for the Mg acceptor in cubic GaN. However, at high C fluxes a deep red luminescence band appeared at 2.1 eV, indicating compensation effects.
Vibrational Spectroscopy of GaN:Mg Under Pressure
Authors: McCluskey M.D. , Zhuravlev K.K. , Kneissl M. , Wong W. , Treat D. , Limpijumnong S. , Walle C.G. Van de , Johnson N.M. 
Published: April 2011

AbstractThe microscopic structure of Mg-H complexes in GaN has been a subject of intense theoretical and experimental investigation. In order to probe the Mg-H structure, we have studied the effect of hydrostatic pressure on the local vibrational mode (LVM) frequency. At ambient pressure, the LVM frequency is 3125 cm-1, which corresponds to a N-H stretching mode. In this study, Fourier-transform spectroscopy was performed on free-standing GaN:Mg,H samples in a diamond-anvil cell, with nitrogen as a pressure-transmitting fluid. The samples had been removed from their sapphire substrate by the laser-liftoff technique. The LVM frequency was measured, at liquid helium temperatures, for pressures ranging from 0 to 5 GPa. The pressure dependence of the frequency is nonlinear: first it decreases with pressure, then it increases. Comparison with first-principles calculations allows us to derive information about the microscopic structure of the Mg-H complex. The calculated stable configuration indeed gives rise to a frequency shift consistent with experiment. Based on the comparison between theory and experiment, we can exclude the bond-center configuration, which would result in a much larger pressure derivative than experimentally observed.
Band-gap engineering in amorphous/microcrystalline ScxGa1-xN.
Authors: Little M. E. , Kordesch M. E. 
Published: April 2011

AbstractReactive sputtering was used to grow thin films of ScxGa1-xN with scandium concentrations of 20%-70% on quartz substrates at temperatures of 300-675 K. X-ray diffraction (XRD) of the films showed either weak or no structure, suggesting the films are amorphous or microcrystalline. Optical absorption spectra were taken of each sample and the optical band gap was determined. The band gap varied linearly with increasing Ga concentration between 2.0 and 3.5 eV. Ellipsometry was used to confirm the band gap measurements and provide optical constants in the range 250-1200 nm. ScN and GaN have different crystal structures (rocksalt and wurzite, respectively), and thus may form a heterogeneous mixture as opposed to an alloy. Since the XRD data were inconclusive, bilayers of ScN/GaN were grown and optical absorption spectra taken. A fundamental difference in the spectra between the bilayer films and alloy films was seen, suggesting the films are alloys, not herterogeneous mixtures.
Growth of Gallium Nitride Textured Films and Nanowires on Polycrystalline Substrates at sub-Atmospheric Pressures
Authors: Chandrasekaran Hari , Sunkara Mahendra K. 
Published: April 2011

AbstractTextured gallium nitride (GaN) films were grown on polished, polycrystalline and amorphous substrates in sub-atmospheric pressures, by direct nitradation of a thin molten gallium films using electron cyclotron resonance (ECR) microwave nitrogen plasma. C-plane texturing was achieved, independent of the substrate crystallinity. Single crystal quality GaN nanowires with diameters ranging from 40-50 nm were also synthesized using direct nitridation of thin gallium films with nitrogen plasma. Scanning electron microscopy (SEM), X-ray Diffraction (XRD), Energy Dispersive Spectroscopy (EDS) and Cross-sectional transmission electron microscopy (CS-TEM), high-resolution TEM (HRTEM) and Micro-Raman spectroscopy were used to characterize the synthesized gallium nitride films and GaN nanowires.
Layer Thickness Dependence of Strain in GaN grown by HVPE
Authors: Sim Gyu Gwang , Yu P. W. , Reynolds D. C. , Look D. C. , Kim Sang Soo , Noh D.Y. 
Published: April 2011

AbstractWurzite GaN epilayers on sapphire substrates usually suffer from biaxial compressive strain due to the mismatches of the thermal expansion coefficients and the lattice constants between GaN layers and sapphire substrates. We have investigated the layer thickness effects on strain and transition energies by photoluminescence (PL), photoreflectance (PR) and X-ray diffraction (XRD). Samples used in this study are grown by hydride vapor phase epitaxy (HVPE) and have the layer thickness of 0.76, 2.6, 5.3 and 48 m. The PL and PR spectra showed the redshift of the transition energies with increasing layer thickness. This is attributed to strain-induced energy shift. The layer thickness dependence of strains is directly observed by XRD. The strain along the c -axis (εzz) decreased with increasing layer thickness. This indicates the strain is relaxed with layer thickness. From strain variation with layer thickness, we suggest that strain relaxation process is rapid at the initial stage of growth and becomes slower as the layer grows. The full width at half maximum (FWHM) of PL spectra and theta rocking curves decrease with increasing layer thickness. This indicates the crystal quality improves as the strain is reduced. Since the strain effect is very small at the layer thickness of 48 μm, we expect zero strain for thicker layers that can potentially be used as substrates for homoepitaxy.
Optical and Structural Properties of Mn-Implanted GaN Films
Authors: Xu J. , Li J. , Zhang R. , Xiu X.Q. , Lu D.Q. , Gu S.L. , Shen B. , Shi Y. , Zheng Y. D. 
Published: April 2011

AbstractThe optical and structural properties of Mn-implanted GaN films have been investigated. The films studied were grown by metal organic chemical vapor deposition (MOCVD), with Mn implanted in 150 KeV, which can offer many distinguished advantages compared with other doping methods. A new energy band with a minimum at 2.9 eV in the reflectance spectra has been observed. The yellow band emission was greatly decreased according to the result of photoluminescence. The structure analysis revealed that the Mn doped sample has good crystal quality as the pure GaN after annealed. And further discussions on the role of Mn in GaN: Mn films have been presented.
New buffer layer technique using underlying epitaxial AlN films for high-quality GaN growth
Authors: Shibata Tomohiko , Kida Yoshihiro , Miyake Hideto , Hiramatsu Kazumasa , Asai Keiichiro , Nagai Teruyo , Sumiya Shigeaki , Tanaka Mitsuhiro , Oda Osamu 
Published: April 2011

AbstractWe demonstrate high-quality epitaxial AlN films on C-plane sapphire as a new buffer layer technique for the growth of high-quality GaN. The obtained GaN films were atomically flat and the full width at half maximum (FWHM) values of the X-ray rocking curve (XRC) were 120arcsec and 510arcsec for (0004) and (10-10), respectively. XRC-FWHM values of the underlying AlN film were 90arcsec and 1800arcsec for (0004) and (10-10), respectively. The XRC results of the GaN indicated that tilted mosaicity of the GaN was much smaller than that of conventional GaN and that small tilted mosaicity coincided with small twisted mosaicity. It was characteristic that the twisted mosaicity drastically reduced from the AlN to the GaN. According to TEM results, it was clarified that the high-quality AlN layer had an effect in reducing the amount of screw-type threading dislocations and that the GaN/AlN interface played an important role in reducing the amount of edge-type dislocations.
Lateral Growth of InN on GaN/Sapphire
Authors: Yang Fuh-Hsiang , Hwang Jih-Hsien , Chen Kuei-Hsien , Yang Ying-Jay 
Published: April 2011

AbstractThe lateral growth of high quality InN on the stripe-pattern GaN/sapphire substrate with an OMVPE system was studied. The surface morphology and structural properties were investigated. Epitaxial films were achieved due to the greatly reduced strain by lateral growth. Two kinds of growth mode were observed due to different growth conditions of V/III ratios. X-ray rocking curve with FWHM of 700 arcsec shows the good quality of the film and E2 mode of Raman spectrum with FWHM of 3.5 cm-1 is among the best results ever reported in the literature.
Fabrication of p-n junction with Mg-doped wide bandgap InAlGaN for application to UV emitters
Authors: Hirayama H. , Yamanaka T. , Kinoshita A. , Hiraoka K. , Hirata A. , Aoyagi Y. 
Published: April 2011

AbstractMg-doped quaternary InAlGaN is very attractive for use as p-side layers of 300-nm band ultraviolet (UV) light-emitting diodes (LEDs) or laser diodes (LDs), because high hole conductivity is expected to obtain for wide bandgap (~4 eV) InAlGaN with Mg-doping. We fabricated p-n junction diode consisting of Mg-doped In0.02Al0.28Ga0.70N and Si-doped Al0.25Ga0.75N, and demonstrated intense UV emission under CW current injection at room temperature. The rising voltage in I-V curve was around 3.8 V and the breakdown voltage was as high as 10 V. Single peaked intense emission was observed at 340 nm from around InAlGaN/AlGaN p-n junction area without any deep level emission. Also we found that Ni/Au electrode directly fabricated on Mg-doped InAlGaN is useful. From these results, Mg-doped InAlGaN is considered to be very attractive for use as p-side layer of UV-LEDs or LDs.
Quaternary AlInGaN MQWs for Ultraviolet LEDs
Authors: Zhang J. P. , Yang J. W. , Adivarahan V. , Wang H. M. , Fareed Q. , Kuokstis E. , Chitnis A. , Shatalov M. , Simin G. , Khan M. Asif , Gaska R. , Shur M. S. 
Published: April 2011

AbstractWe report a pulsed atomic layer epitaxy (PALE) growth technique for quaternary AlInGaN films for ultraviolet optoelectronic applications. Using the PALE approach high quality quaternary AlInGaN/AlInGaN multiple quantum wells (MQWs) were successfully grown over sapphire substrates. From X-ray diffraction, atomic force microscopy, and photoluminescence study, a high structural and optical quality was established for the AlInGaN MQWs. Incorporating the PALE grown quaternary MQWs as the active layer of light emitting diode (LED) on sapphire or SiC substrates we also demonstrated room temperature deep ultraviolet electroluminescence under dc and pulsed electrical pumping. The peak emission wavelength can be tuned from 305 nm to 340 nm with spectrum FWHM of about 20 nm by varying the alloy compositions of the quaternary AlInGaN active layers using PALE. Comparative study of LEDs over sapphire and SiC substrates was also done in order to determine the influence of epilayer design on the performance parameters and the role of the substrate absorption.
Raman Studies of GaNP Alloy
Authors: Buyanova I. A. , Chen W. M. , Goldys E. M. , Xin H. P. , Tu C. W. 
Published: April 2011

AbstractRaman scattering (RS) spectroscopy is employed to characterize the effect of nitrogen on structural properties of GaNxP1-x alloy with nitrogen composition up to 3 %. Two-mode behavior of the alloy is clearly shown. The frequency of the GaP-like LO phonons is found to decrease with N composition as –1.13 cm-1x. This dependence is proposed to be largely due to the biaxial strain in the GaNP epilayers, as a result of lattice mismatch to the GaP substrate. The frequency of the GaN-like phonons is found to be more sensitive to nitrogen content, increasing with the rate of +2.6 cm-1x. The addition of nitrogen is also found to cause a dramatic quenching of the two-phonon Raman scattering and an appearance of the zone edge GaP-like vibrations. These effects are suggested to reflect local distortion in the GaNP lattice induced by nitrogen, as well as possible clustering of N atoms.
Influence of growth temperature on emission efficiency of InGaN/GaN multiple quantum wells
Authors: Chen Fei , Cartwright A. N. , Sweeney Paul M. , Cheung M. C. , Flynn Jeffrey S. , Keogh David 
Published: April 2011

AbstractA comparative study, using time-resolved and CW photoluminescence spectroscopy, of MOVPE grown InGaN/GaN multiple quantum wells deposited on HVPE GaN/Sapphire at different growth temperatures was undertaken. It was found that the PL linewidth increased and the peak emission energy decreased as the growth temperature was reduced. Moreover, the sample grown at an intermediate growth temperature exhibited total integrated luminescence intensity much greater than the samples grown at higher or lower growth temperatures. A phenomenological carrier recombination dynamics model based on the competition of quantum well-like radative recombination, spatially localized radiative recombination in potential minima and non-radiative recombination through defects is presented to provide an explanation of the observed emission dynamics and efficiency. In this model, the emission efficiency is determined by the relative area of defects and the number density of localized states in the potential minima, both of which are influenced by the growth temperature. Furthermore, the photon energy dependent lifetimes are well fitted with this model by assuming a Gaussian shape localized states distribution. The localized potential minima are consistent with nanoscale indium rich regions due to indium aggregation.
Excitons bound to structural defects in GaN
Authors: Reshchikov M. A. , Huang D. , Yun F. , Morkoç H. , Molnar R. J. , Litton C. W. 
Published: April 2011

AbstractWe analyzed the photoluminescence (PL) spectra of undoped GaN films grown by molecular beam epitaxy on sapphire substrates. While the PL spectra from high-quality samples contain free and bound exciton peaks only, the spectra from some samples involve sharp unidentified peaks in the energy range of 3.0 – 3.45 eV, specifically at 3.21, 3.32, 3.36, and 3.42 eV. We attribute these peaks to excitons bound to defects because of the linear and sometimes superlinear increase in their intensity with excitation density without saturation up to 100 W/cm2. With increasing temperature these peaks quench in a well-known fashion similar to that for excitons. In order to relate the observed peaks to the structural defects, we etched selected samples in hot H3PO4 acid or, alternatively, with photo-electrochemical (PEC) etching at room temperature in the presence of UV-illumination in a dilute KOH solution. In the former case the dislocations were etched leaving etched pits on the surface, while in the latter case the dislocations remained unetched due to a deficit of photogenerated holes at dislocation sites. We found that the 3.42 eV peak disappeared after both hot wet and PEC etching suggesting that the associated defect is at the GaN surface. Peaks at 3.21 and 3.36 eV could be enhanced greatly by PEC etching, which were correlated to bulk dislocations.