bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spectroscopic Ellipsometry Analysis of InGaN/GaN and AlGaN/GaN Heterostructures Using a Parametric Dielectric Function Model
Authors: Wagner J. , Ramakrishnan A. , Obloh H. , Kunzer M. , Köhler K. , Johs B. 
Published: September 2012

AbstractSpectroscopic ellipsometry (SE) has been used for the characterization of AlGaN/GaN and InGaN/GaN heterostructures. The resulting pseudodielectric function spectra were analyzed using a multilayer approach, describing the dielectric functions of the individual layers by a parametric oscillator model. From this analysis, the dielectric function spectra of GaN, AlxGa1−xN (x≤0.16), and In0.13Ga0.87N were deduced. Further, the dependence of the AlxGa1−xN band gap energy on the Al mole fraction was derived and compared with photoluminescence data recorded on the same material. The SE band gap data are compatible with a bowing parameter close to 1 eV for the composition dependence of the AlxGa1−xN gap energy. Finally, the parametric dielectric functions have been used to model the pseudodielectric function spectrum of a complete GaN/AlGaN/InGaN LED structure.
Dynamics of Anomalous Temperature-Induced Emission Shift in MOCVD-grown (Al, In)GaN Thin Films
Authors: Cho Yong-Hoon , Gainer G. H. , Lam J. B. , Song J. J. , Yang W. , Jhe W. 
Published: September 2012

AbstractWe present a comprehensive study of the optical characteristics of (Al, In)GaN epilayers measured by photoluminescence (PL), integrated PL intensity, and time-resolved PL spectroscopy. For not only InGaN, but also AlGaN epilayers with large Al content, we observed an anomalous PL temperature dependence: (i) an “S-shaped” PL peak energy shift (decrease-increase-decrease) and (ii) an “inverted S-shaped” full width at half maximum (FWHM) change (increase-decrease-increase) with increasing temperature. Based on time-resolved PL, the S shape (inverted S shape) of the PL peak position (FWHM) as a function of temperature, and the much smaller PL intensity decrease in the temperature range showing the anomalous emission behavior, we conclude that strong localization of carriers occurs in InGaN and even in AlGaN with rather high Al content. We observed that the following increase with increasing Al content in AlGaN epilayers: (i) a Stokes shift between the PL peak energy and the absorption edge, (ii) a redshift of the emission with decay time, (iii) the deviations of the PL peak energy, FWHM, and PL intensity from their typical temperature dependence, and (iv) the corresponding temperature range of the anomalous emission behavior. This indicates that the band-gap fluctuation responsible for these characteristics is due to energy tail states caused by non-random inhomogeneous alloy potential variations enhanced with increasing Al content.
Time-Resolved Spectroscopy of InGaN
Authors: Pophristic Milan , Long Frederick H. , Tran Chuong , Ferguson Ian T. 
Published: September 2012

AbstractWe have used time-resolved photoluminescence (PL), with 400 nm (3.1 eV) excitation, to examine InxGa1−xN/GaN light-emitting diodes (LEDs) before the final stages of processing at room temperature. We have found dramatic differences in the time-resolved kinetics between dim, bright and super bright LED devices. The lifetime of the emission for dim LEDs is quite short, 110 ± 20 ps at photoluminescence (PL) maximum, and the kinetics are not dependent upon wavelength. This lifetime is short compared to bright and super bright LEDs, which we have examined under similar conditions. The kinetics of bright and super bright LEDs are clearly wavelength dependent, highly non-exponential, and are on the nanosecond time scale (lifetimes are in order of 1 ns for bright and 10 ns for super bright LED at the PL max). The non-exponential PL kinetics can be described by a stretched exponential function, indicating significant disorder in the material. Typical values for β, the stretching coefficient, are 0.45 – 0.6 for bright LEDs, at the PL maxima at room temperature. We attribute this disorder to indium alloy fluctuations.From analysis of the stretched exponential kinetics we estimate the potential fluctuations to be approximately 75 meV in the super bright LED. Assuming a hopping mechanism, the average distance between indium quantum dots in the super bright LED is estimated to be 20 Å.
High Density Plasma Damage Induced in n-GaN Schottky Diodes Using Cl2/Ar Discharges
Authors: Zhang A.P. , Dang G. , Ren F. , Cao X.A. , Cho H. , Lambers E.S. , Pearton S.J. , Shul R.J. , Zhang L. , Baca A.G. , Hickman R. , Hove J.M. Van 
Published: September 2012

AbstractThe effects of dc chuck self-bias and high density source power (which predominantly control ion energy and ion flux, respectively) on the electrical properties of n-GaN Schottky diodes exposed to Inductively Coupled Plasma of Cl2/Ar were examined. Both parameters were found to influence the diode performance, by reducing the reverse breakdown voltage and Schottky barrier height. All plasma conditions were found to produce a nitrogen-deficient surface, with a typical depth of the non-stoichiometry being ∼500 Å. Post-etch annealing was found to partially restore the diode characteristics.
Wet Etching of Ion-implanted GaN Crystals by AZ-400K Photoresist
Authors: Carosella C.A. , Molnar B. , Schiestel S. , Sprague J.A. 
Published: September 2012

AbstractThe photoresist developer AZ-400K, commonly used to remove AlN encapsulant layers on GaN crystalline films, is found to also etch certain as-grown GaN films. Even as-grown GaN films, which can not be etched in AZ-400K, however can be etched if amorphized by ion implantation. Etch rates of as high as 450 Å/min. were observed. The etching proceeds linearly in GaN in the first few minutes to a depth corresponding to the depth of the amorphous region. Subsequently, the etching rate saturates. Annealing of the highly amorphized samples up to 1000°C for one minute in a N2/H2 gas mixture does not reduce the etch rate, but for lower doses we observed a reduction of the etch rate. Observations of etching depth under various ion-implanted conditions could be correlated with the number of displacements per atoms (dpa) required for amorphization.
Oxidation of Gallium Nitride Epilayers in Dry Oxygen
Authors: Chen P. , Zhang R. , Xu X.F. , Chen Z.Z. , Zhou Y.G. , Xie S.Y. , Shi Y. , Shen B. , Gu S.L. , Huang Z.C. , Hu J. , Zheng Y.D. 
Published: September 2012

AbstractThe oxidation of GaN epilayers in dry oxygen has been studied. The 1-μm-thick GaN epilayers grown on (0001) sapphire substrates by Rapid-Thermal-Processing/Low Pressure Metalorganic Chemical Vapor Deposition were used in this work. The oxidation of GaN in dry oxygen was performed at various temperatures for different time. The oxide was identified as the monoclinic β-Ga2O3 by a θ-2θ scan X-ray diffraction (XRD). The scanning electron microscope observation shows a rough oxide surface and an expansion of the volume. XRD data also showed that the oxidation of GaN began to occur at 800°C. The GaN diffraction peaks disappeared at 1050°C for 4 h or at 1100°C for 1 h, which indicates that the GaN epilayers has been completely oxidized. From these results, it was found that the oxidation of GaN in dry oxygen was not layer-by-layer and limited by the interfacial reaction and diffusion mechanism at different temperatures.
A Damage-Reduced Process Revealed by Photoluminescence in Photoelectrochemical Etching GaN
Authors: Hwang J. M. , Hsieh J. T. , Hwang H. L. , Hung W. H. 
Published: September 2012

AbstractPhotoelectrochemical (PEC) etching technique has been proven to be an effective method to etch GaN. Despite its success, investigations on etching-induced damage are still scare. In this work, the damage induced by PEC etching of GaN in KOH electrolyte was studied. Photoluminescence (PL) spectroscopy was used to explore the origin of etching-induced damaged layer. From the variable temperature PL measurements, the origin of etching-induced damage was attributed to be the defect complex of VGa-ON (gallium vacancy bonds to oxygeon on nitrogen antisite). With determination of the defect origin, the electronic transition in the etch damage-related yellow luminescence (YL) band was suggested to be deep donor-like state to shallow-acceptor transition. In addition, a post-treatment method with boiled KOH chemical etching was developed to remove the thin damaged layer. In this method, crystallographic etching characteristics of boiled KOH was observed to assist in the formation of smooth sidewall facets. As revealed by the reduction of yellow luminescence, we propose this novel technique as a near damage-free etching method.
Fabrication and Characterization of InGaN Nano-scale Dots for Blue and Green LED Applications
Authors: Kim K.S. , Hong C.-H. , Lee W.-H. , Kim C.S. , Cha O.H. , Yang G.M. , Suh E.-K. , Lim K.Y. , Lee H.J. , Cho H.K. , Lee J.Y. , Seo J.M. 
Published: September 2012

AbstractThin layers of InGaN were grown by metalorganic chemical vapor deposition and characterized with atomic force microscopy and high-resolution transmission electron microscopy. InGaN deposited on GaN exhibits a Stranski-Krastanov growth mode, including 2D wetting layer and 3D self-assembled quantum dots. Besides, we observed that the formed InGaN nano-scale dots have a trapezoidal shape with a {1-102} facet with respect to (0002) surface. Visible spectral range from UV to green was easily obtained by changing InGaN quantum well thickness up to 2.3 nm.
The Microstructure and Electrical Properties of Directly Deposited TiN Ohmic Contacts to Gallium Nitride.
Authors: Ruterana P. , Nouet G. , Kehagias Th. , Komninou Ph. , Karakostas Th. , Poisson M.A. di Forte , Huet F. 
Published: September 2012

AbstractWhen the stoichiometric TiN was deposited directly on GaN, we obtained columnar TiN grains of 5-20 nm section which cross the whole film thickness and are rotated mostly around the [111] axis. The conventional epitaxial relationship is obtained and no amorphous patches are observed at the interface. The deposition of TiN on Si doped GaN layers lead to the formation of an ohmic contact, whereas we obtain a rectifying contact on p type layers.
Highly Chemical Reactive Ion Etching of Gallium Nitride
Authors: Karouta F. , Jacobs B. , Moerman I. , Jacobs K. , Weyher J.L. , Porowski S. , Crane R. , Hageman P.R. 
Published: September 2012

Abstract: A highly chemical reactive ion etching process has been developed for MOVPE-grown GaN on sapphire. The key element for the enhancement of the chemical property during etching is the use of a fluorine containing gas in a chlorine based chemistry. In the perspective of using GaN substrates for homo-epitaxy of high quality GaN/AlGaN structures we have used the above described RIE process to smoothen Ga-polar GaN substrates. The RMS value, measured by AFM, went from 20 Å (after mechanical polishing) down to 4 Å after 6 minutes of RIE. Etching N-polar GaN resulted in a higher etch rate than Ga-polar materials (165 vs. 110 nm/min) but the resulting surface was quite rough and suffers from instability problems. Heat treatment and HCl dip showed a partial recovery of Schottky characteristics after RIE.
Improved Low Resistance Contacts of Ni/Au and Pd/Au to P-Type GaN Using a Cryogenic Treatment
Authors: Park Mi-Ran , Anderson Wayne A. , Park Seong-Ju 
Published: September 2012

AbstractA low resistance Ohmic contact to p-type GaN is essential for reliable operation of electronic and optoelectronic devices. Such contacts have been made using Ni/Au and Pd / Au contacts to p-type Mg-doped GaN (1.41×1017 cm−3) grown by metalorganic chemical vapor deposition ( MOCVD ) on ( 0001 ) sapphire substrates. Thermal evaporation was used for the deposition of those metals followed by annealing at temperatures of 400 ∼ 700 °C in an oxygen and nitrogen mixed gas ambient, then subsequently cooled in liquid nitrogen which reduced the specific contact resistance from the range of 9.46∼2.80×10−2 ωcm2 to 9.84∼2.65×10−4 ωcm2 for Ni/Au and from the range of 8.35∼5.01×10−4 ωcm2 to 3.34∼1.80×10−4 ωcm2 for Pd/Au. The electrical characteristics for the contacts were examined by the current versus voltage curves and the specific contact resistance was determined by use of the circular transmission line method (c-TLM). The effects of the cryogenic process on improving Ohmic behavior (I-V linearity) and reducing the specific contact resistance will be discussed from a microstructural analysis which reveals the metallurgy of Ohmic contact formation.
Deep Centers and Persistent Photoconductivity Studies in Variously Grown GaN Films
Authors: Polyakov Alexander Y. , Smirnov Nikolai B. , Govorkov Anatoliy V. , Usikov Alexander S. , Shmidt Natalie M. , Pushnyi Boris V. , Tsvetkov Denis V. , Stepanov Sergey I. , Dmitriev Vladimir A. , Mil'vidskii Mikhail G. , Pavlov Vladimir F. 
Published: September 2012

AbstractDeep levels studies on a set of n-GaN films grown by MOCVD and HVPE reveal the presence of electron traps with levels near Ec-0.25 eV, Ec-0.55 eV, Ec-0.8 eV, Ec-1 eV, hole traps with levels near Ev+0.9 eV and a band of relatively shallow states in the lower half of the bandgap. The total density of these latter states was estimated to be some 1016 cm−3 and they were tentatively associated with dislocations in GaN based on their high concentration and band-like character. None of the electron or hole traps could be unambiguously related with strong changes of diffusion lengths of minority carriers in various samples. It is proposed that such changes occur due to different surface recombination velocities. An important role of Ec-0.55 eV traps in persistent photoconductivity phenomena in n-GaN has been demonstrated.
Photocurrent Spectroscopy Investigations of Mg-Related Defects Levels in p-Type GaN
Authors: Chung S. J. , Cha O. H. , Cho H. K. , Jeong M. S. , Hong C-H. , Suh E-K. , Lee H. J. 
Published: September 2012

AbstractThe defect levels associated with Mg impurity in p-type GaN films were systematically investigated in terms of doping concentration by photocurrent spectroscopy. Mg-doped GaN samples were grown on sapphire substrate by metal organic chemical vapor deposition and annealed in nitrogen atmosphere at 850 for 10 minutes. At room temperature, PC spectra showed two peaks at 3.31 and 3.15 eV associated with acceptor levels formed at 300 and 142 meV above valence band in as grown samples. But, after the thermal annealing, PC spectra exhibited various additional peaks depending on the Mg concentration. In the GaN samples with Mg concentration around 6 7 1017 cm−3, we have observed PC peaks related to Mg at 3.31 as well as 3.02 eV and carbon acceptor at 3.17 eV. For moderately Mg doped GaN samples, i.e., the hole concentration p=3 4 1017 cm−3, additional peak was observed at around 0.9 eV which can be attributed to defects related to Ga vacancy. For relatively low Mg doped samples whose hole concentrations are 1 2 1017 cm−3, additional broad peak was observed at around 1.3 eV. This peak may be related to the yellow band luminescence. As the Mg concentration is increased, the concentration of Ga vacancies can be reduced because Mg occupies the substitutional site of Ga in GaN lattice. When the hole concentration is above 6 7 1017 cm−3, the yellow luminescence and Ga vacancy related peaks disappeared completely.
Characteristics of Deep Centers Observed in n-GaN Grown by Reactive Molecular Beam Epitaxy
Authors: Fang Z-Q. , Look D. C. , Kim Wook , Morkoç H. 
Published: September 2012

AbstractDeep centers in Si-doped n-GaN samples grown on sapphire by reactive molecular beam epitaxy, using different ammonia flow rates (AFRs), have been studied by deep level transient spectroscopy. In addition to five electron traps, which were also found in n-GaN layers grown by both metalorganic chemical-vapor deposition and hydride vapor-phase epitaxy, two new centers C1 (0.43-0.48 eV) and E1 (0.25 eV) have been observed. C1, whose parameters show strong electric-field effects and anomalous electron capture kinetics, might be associated with dislocations. E1, which is very dependent on the AFR, exhibits an activation energy close to that of a center created by electron irradiation and is believed to be a defect complex involving VN.
Comparison Study of Structural and Optical Properties of InxGa1-xN/GaN Quantum Wells with Different in Compositions
Authors: Kwon Yong-Hwan , Gainer G. H. , Bidnyk S. , Cho Y. H. , Song J. J. , Hansen M. , Denbaars S. P. 
Published: September 2012

AbstractThe effect of In on the structural and optical properties of InxGa1−xN/GaN multiple quantum wells (MQWs) was investigated. These were five-period MQWs grown on sapphire by metalorganic chemical vapor deposition. Increasing the In composition caused broadening of the high-resolution x-ray diffraction superlattice satellite peak and the photoluminescence-excitation bandedge. This indicates that the higher In content degrades the interface quality because of nonuniform In incorporation into the GaN layer. However, the samples with higher In compositions have lower room temperature (RT) stimulated (SE) threshold densities and lower nonradiative recombination rates. The lower RT SE threshold densities of the higher In samples show that the suppression of nonradiative recombination by In overcomes the drawback of greater interface imperfection.
Emission at 247 nm from GaN Quantum Wells Grown by MOCVD
Authors: Someya Takao , Hoshino Katsuyuki , Harris Janet C. , Tachibana Koichi , Kako Satoshi , Arakawa Yasuhiko 
Published: September 2012

AbstractPhotoluminescence (PL) spectra were measured at room temperature for GaN quantum wells (QWs) with Al0.8Ga0.2N barriers, which were grown by atmospheric-pressure metal organic chemical vapor deposition (MOCVD). The thickness of the GaN QW layers was systematically varied from one monolayer to four monolayers. We clearly observed a PL peak at a wavelength as short as 247 nm (5.03 eV) from one monolayer-thick QWs. The effective confinement energy is as large as 1.63 eV.
Pendeo-Epitaxial Growth and Characterization of GaN and Related Materials on 6H-SiC(0001) and Si(111) Substrates
Authors: Davis Robert F. , Gehrke T. , Linthicum K.J. , Zheleva T. S. , Rajagopal P. , Zorman C. A. , Mehregany M. 
Published: September 2012

AbstractDiscrete and coalesced monocrystalline GaN and AlxGa1−xN layers grown via Pendeoepitaxy (PE) [1] originated from side walls of GaN seed structures containing SiNx top masks have been grown via organometallic vapor phase deposition on GaN/AlN/6HSiC(0001) and GaN(0001)/AlN(0001)/3C-SiC(111)/Si(111) substrates. Scanning and transmission electron microscopies were used to evaluate the external microstructures and the distribution of dislocations, respectively. The dislocation densities in the PE grown films was reduced by at least five orders of magnitude relative to the initial GaN seed layers. Tilting in the coalesced GaN epilayers was observed via X-ray diffraction. A tilt of 0.2° was confined to areas of mask overgrowth; however, no tilting was observed in the material suspended above the SiC substrate. The strong, low-temperature PL band-edge peak at 3.45 eV with a FWHM of 17 meV was comparable to that observed in PE GaN films grown on 6H-SiC(0001). The band-edge in the GaN grown on AlN(0001)/SiC(111)Si(111) substrates was shifted to a lower energy by 10 meV, indicative of a greater tensile stress.
Fabrication of GaN with Buried Tungsten (W) Structures Using Epitaxial Lateral Overgrowth (ELO) via LP-MOVPE
Authors: Miyake Hideto , Yamaguchi Motoo , Haino Masahiro , Motogaito Atsushi , Hiramatsu Kazumasa , Nambu Shingo , Kawaguchi Yasutoshi , Sawaki Nobuhiko , Iyechika Yasushi , Maeda Takayoshi , Akasaki Isamu 
Published: September 2012

AbstractA buried tungsten (W) mask structure with GaN is successfully obtained by epitaxial lateral overgrowth (ELO) technique via low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). The selectivity of GaN growth on the window region vs. the mask region is good. An underlying GaN with a striped W metal mask is easily decomposed above 500 °C by the W catalytic effect, by which radical hydrogen is reacted with GaN. It is difficult to bury the W mask because severe damage occurs in the GaN epilayer under the mask. It is found that an underlying AlGaN/GaN layer with a narrow W stripe mask width (mask/window = 2/2 νm) leads the ELO GaN layer to be free from damage, resulting in an excellent W-buried structure.
Advanced Pendeoepitaxy™ of GaN and AlxGa1−xN Thin Films on SiC(0001) and Si(111) Substrates via Metalorganic Chemical Vapor Deposition
Authors: Gehrke T. , Linthicum K. J. , Rajagopal P. , Preble E. A. , Davis R. F. 
Published: September 2012

AbstractGrowth of GaN and AlxGa1−xN thin films on 6H-SiC(0001) and Si(111) substrates with low densities of defects using the PENDEO™ process and the characterization of the resulting materials are reported. The application of a mask on the GaN seed structures hinders the vertical propagation of threading dislocations of the seed material during regrowth, but introduces a misregistry in the overgrowing material resulting in low quality crystal growth. This misregistry has been eliminated due to advanced processing and the exclusion of the masking layer. The new generation of samples do not show any misregistry, as shown by transmission electron microscopy.
GaN and AlN Layers Grown by Nano Epitaxial Lateral Overgrowth Technique on Porous Substrates
Authors: Mynbaeva M. , Titkov A. , Kryzhanovski A. , Zubrilov A. , Ratnikov V. , Davydov V. , Kuznetsov N. , Mynbaev K. , Stepanov S. , Cherenkov A. , Kotousova I. , Tsvetkov D. , Dmitriev V. 
Published: September 2012

AbstractDefect density and stress reduction in heteroepitaxial GaN and AlN materials is one of the main issues in group III nitride technology. Recently, significant progress in defect density reduction in GaN layers has been achieved using lateral overgrowth technique. In this paper, we describe a novel technique based on nano-scale epitaxial lateral overgrowth.GaN layers were overgrown by hydride vapour phase epitaxy (HVPE) on porous GaN. Porous GaN was formed by anodization of GaN layers grown previously on SiC ŝubstrates. Pore's size was in nano-scale range.Thickness of overgrown layers ranged from 2 to 120 microns. It was shown that GaN layers overgrown on porous GaN have good surface morphology and high crystalline quality. The surface of overgrown GaN material was uniform and flat without any traces of porous structure. Raman spectroscopy measurements indicated that the stress in the layers grown on porous GaN was reduced down to 0.1 - 0.2 GPa, while the stress in the layers grown directly on 6H-SiC substrates remains at its usual level of about 1.3 GPa.Preliminary experiments were done on HVPE growth of AlN layer on porous substrates. Improvement of surface morphology and crack density reduction has been observed.
Mass Transport, Faceting and Behavior of Dislocations in GaN
Authors: Nitta S. , Kashima T. , Kariya M. , Yukawa Y. , Yamaguchi S. , Amano H. , Akasaki I. 
Published: September 2012

AbstractThe behavior of threading dislocations during mass transport of GaN was investigated in detail by transmission electron microscopy. Mass transport occurred at the surface. Therefore, growing species are supplied from the in-plane direction. The behavior of threading dislocations was found to be strongly affected by the mass transport process as well as the high crystallographic anisotropy of the surface energy of the facets particular to GaN.