bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical and Structural Analysis of Nitridated Sapphire
Authors: Cho Y. , Rouvimov S. , Kim Y. , Liliental-Weber Z. , Weber E. R. 
Published: April 2011

AbstractThe incorporation of nitrogen into sapphire substrates during nitridation was studied by xray photoelectron spectroscopy (XPS). An increase in the intensity of nitrogen 1s peak in XPS was observed upon longer nitridation. The surface morphology of the substrates was characterized by atomic force microscopy (AFM). High resolution electron microscopy (HREM) was employed for structural analysis. The cross sectional TEM showed a thin layer of AlN buried between amorphous AlNxO1−x and sapphire. This is the first direct observation of AlN on sapphire. The TEM images show a deeper penetration depth of nitrogen into a longer nitridated sapphire.
Effect Of Mg, Zn, Si, And O On The Lattice Constant of Gallium Nitride Thin Films
Authors: Sudhir G. S. , Peyrot Y. , Krüger J. , Kim Y. , Klockenbrink R. , Kisielowski C. , Rubin M. D. , Weber E. R. , Kriegseis W. , Meyer B. K. 
Published: April 2011

AbstractThis study analyzes the impact of most common impurities and dopants on the c lattice parameter for thin films of Gallium Nitride (GaN) deposited on basal plane sapphire. Both Mg (∼1017 cm-3) and Zn (∼3 × 1020 cm-3) doping were found to expand the c lattice parameter as much as +0.38% and +0.62%, respectively. On the contrary, Oxygen up to concentrations 9 1021 cm-3 is shown to replace N in GaN thin films reducing the c parameter only by a small amount. Incorporation of Si leads to a large decrease of the c parameter which can not be attributed to the different size of Ga and Si atom. It is suggested that doping alters the film stoichiometry by a predicted Fermi level dependence of defect formation energies. The impact of stoichiometry on c lattice parameter and the effect of hydrostatic strain on resistivity in undoped and doped GaN is discussed.
Time-Resolved Photoluminescence of GaN / Ga0.93Al0 .07N Quantum Wells
Authors: Lefebvre P. , Allègre J. , Gil B. , Kavokine A. , Mathieu H. , Kim W. , Salvador A. , Botchkarev A. , Morkoç H. 
Published: April 2011

AbstractThe recombination dynamics of excitons in GaN / Ga0.93Al0.07N multiple quantum wells is studied versus lattice temperature. The average decay time of photoluminescence measured at 8K is of ∼330 ps, with a substantial variation of times within the emission line. This is interpreted in terms of carrier localization due to alloy disorder and to well width and depth variations. The radiative lifetime τr of excitons in the wells is found to increase linearly with temperature, with ∂τr / ∂T = 20.5 ± 0.7 ps.K−1. The radiative lifetime of free excitons in the low-temperature limit is deduced to be 2.4 ps, consistent with a longitudinal-transverse splitting ћωLT in GaN of 0.6 meV, in excellent agreement with recent estimations. The ratio of the lifetimes of localized and free excitons is found coherent with the picture of electrons and holes independently localized on short-range defects, instead of excitons localized as a whole on long-range potential fluctuations.
Well Thickness And Doping Effects, And Room Temperature emission mechanisms in InGaN/GaN And GaN/AlGaN Multiple Quantum Wells
Authors: Zeng K. C. , Smith M. , Lin J. Y. , Jiang H. X. , Tang H. , Salvador A. , Kim W. , Morkoc H. , Khan M. Asif 
Published: April 2011

AbstractEffects of well thickness and Si-doping on the photoluminescence (PL) emission properties of GaN/AlxGa1-xN (x ∼ 0.07) and InxGa1-xN/GaN (x ∼ 0.15–0.2) multiple quantum wells (MQWs) grown both by MOCVD and reactive MBE have been studied. The room temperature emission mechanisms have also been addressed.
Depth-Resolved and Excitation Power Dependent Cathodo-Luminescence of MBE Grown Cubic GaN Epilayers
Authors: As D. J. , Wang C. , Schöttker B. , Schikora D. , Lischka K. 
Published: April 2011

AbstractWe present a detailed investigation of the cathodoluminescence (CL) of MBEgrown cubic GaN (c-GaN) epitaxial layers. Under high excitation conditions the room temperature CL-spectrum is dominated by a single excitonic emission band at about 3.21 eV with a full width at half maximum of 55 meV. Under low electron beam excitation a second, deep emission band at 2.4 eV is observable. A strong variation of the ratio between the deep luminescence intensity and the near band edge luminescence intensity ratio is observed with increasing excitation intensity. Using a simple model based on bimolecular rate equations the concentration of defects involved in this transition is estimated to be about 1015 cm−3. CL-measurements with varying excitation intensity reveal that these recombination levels have only minor influence on the performance of high injection optoelectronic devices like laser diodes. Depth resolved measurements and CL-images from a cleaved c-GaN/GaAs reveal that the deep recombination centers are homogeneously distributed within the epilayer, however the concentration of nonradiative recombination centers is increasing towards the GaN/GaAs interface.
Cross-sectional cathodoluminescence of GaN epitaxial films
Authors: Zaldivar M. Herrera , Fernández P. , Piqueras J. 
Published: April 2011

AbstractCathodoluminescence (CL) in the scanning electron microscope has been used to investigate the variation along the growth axis direction of luminescence emission from epitaxial GaN films. CL spectra recorded at different positions of the sample cross-section as well as monochromatic CL images show strong spatial variations of the different luminescence emissions along the growth axis. At the buffer layer-substrate interface and at the top part of the sample, which corresponds to a Si doped epilayer, enhanced CL emission is observed as compared with the relatively low emission in the central region of the cross-section. The nature of the defects responsible for the observed CL distribution is discussed.
Luminescence Of A New Material: GaN Grown On NdGaO3
Authors: Korona K. P. , Pakula K. , Wysmolek A. , Baranowski J. M. , Bergman J. P. , Monemar B. , Łukasiewicz T. , Łuczyński Z. 
Published: April 2011

AbstractIt is shown that heteroepitaxial GaN layers grown on NdGaO3, in spite of a very high conductivity (˜ 10 Ω−1cm−1) have very efficient luminescence properties. It is shown that a high electrical conductivity is caused by contamination of GaN layers with oxygen. Efficient emission due to donor bound excitons (at hv = 3.475 eV), free excitons and free electron – hole recombination have been identified. The total PL emission in the exciton region exceeds the intensity from the homoepitaxial GaN layers. It is argued that a high oxygen concentration eliminates nonradiative channels connected with point defects, leading to efficient radiative recombination.
Excitonic Enhanced Optical Gain Of GaN/AlGaN Quantum Wells With Localized States
Authors: Uenoyama Takeshi 
Published: April 2011

AbstractWe have evaluated the optical gain of GaN/AlGaN quantum well structures with localized states, taking into account the Coulomb interaction. The localized states axe introduced in the well as quantum dot-like subband states. We have used the temperature Green's function formalism to treat the many-body effects and have found a new excitonic enhancement of the optical gain involved the localized states. This enhancement is stronger than the conventional Coulomb enhancement. It might play an important role to reduce the threshold carrier density.
Dislocations In GaN/Sapphire: Their Distribution And Effect On Stress And Optical Properties
Authors: Jain S. C. , Pinardi K. , Maes H. E. , overstraeten R. Van , Willander M. , Atkinson A. 
Published: April 2011

AbstractRecent Raman experiments show that strain in GaN layers grown on the c-plane of sapphire is low at the surface, increases with depth, and is maximum at the interface. We show that this stress distribution can be attributed to the presence of a large number of threading dislocations. GaN photonic devices work in spite of large density of dislocations present in the GaN epilayers. We describe a model which shows that the effect of saturation of traps in the dislocations with increasing number of injected carriers can explain the high performance of the GaN devices containing the dislocations.
Effects of Substrate Orientation on the Valence Band Splittings and Valence Band Offsets in GaN and AlN Films
Authors: Majewski J. A. , Städele M. 
Published: April 2011

AbstractWe present a first-principles study of heteroepitaxial interfaces between GaN and both cubic as well as wurtzite AlN substrates oriented along main cubic or hexagonal directions and of stacking fault interfaces between cubic and wurtzite GaN. Our calculations show that all studied heterostructures are of type I. Valence band offsets for GaN/AlN are nearly independent of the substrate orientation and of the order of 0.8 eV. The valence and conduction band offsets for a stacking fault interface are predicted to be 40 meV and 175 meV, respectively.
Phase Separation in InGaN/GaN Multiple Quantum Wells
Authors: Mccluskey M. D. , Romano L. T. , Krusor B. S. , Bour D. P. , Chua C. , Johnson N. M. , Yu Kin Man 
Published: April 2011

AbstractEvidence is presented for phase separation in In0.27Ga0.73N/GaN multiple quantum wells (MQW's). After annealing for 4 min at a temperature of 1100 °C, the absorption threshold at 2.95 eV is replaced by a broad peak at 2.65 eV. This peak is attributed to the formation of Inrich InGaN phases in the active region. X-ray diffraction measurements show a shift in the diffraction peaks toward GaN, consistent with the formation of an In-poor phase.
Photoluminescence of Wet- and Dry-Etched Gallium Nitride
Authors: Reuter E. E. , Youtsey C. , Adesida I. , Bishop S. G. 
Published: April 2011

AbstractThe photoluminescence (PL) of GaN grown on SiC is studied as a function of etch depth for two types of etches, photoelectrochemical and chemically assisted ion beam. It is found that as the etch proceeds deeper toward the substrate, the PL exhibits an increasing blue-shift and an increase in emission intensity of the donor acceptor pair band, which indicates increasing biaxial compressive stress and increasing impurity concentration near the substrate. The PL spectra of the dry etched GaN tended to have slightly higher intensities than comparably wet etched GaN.
Comparison Of Dry-Etch Techniques For Gan, Inn, And Ain
Authors: Shul R. J. , Vawter G. A. , Willison C. G. , Bridges M. M. , Lee J. W. , Pearton S. J. , Abernathy C. R. 
Published: April 2011

AbstractFabrication of group-III nitride devices relies on the ability to pattern features to depths ranging from ∼1000 Å to > 5 μm with anisotropic profiles, smooth morphologies, selective etching of one material over another, and a low degree of plasma-induced damage. In this study, GaN etch rates and etch profiles are compared using reactive ion etch (RIE), reactive ion beam etching (RIBE), electron cyclotron resonance (ECR), and inductively coupled plasma (ICP) etch systems. RIE yielded the slowest etch rates and sloped etch profiles despite dc-biases > −900 V. ECR and ICP etching yielded the highest rates with anisotropic profiles due to their high plasma flux and the ability to control ion energies independently of plasma density. RIBE etch results also showed anisotropic profiles with slower etch rates than either ECR or ICP possibly due to lower ion flux. InN and AIN etch characteristics are also compared using ICP and RIBE.
SiC Epitaxial Growth on Carbon
Authors: Khlebnikov I. , Madangarli V. , Sudarshan T. S. 
Published: April 2011

AbstractThe possibility of single crystal SiC expitaxial growth on freestanding amorphous carbon films (500–1000 Å) as well as thin amorphous carbon layers deposited on mono-crystalline SiC seeds, by conventional physical vapor transport (PVT) technique, is demonstrated. Preliminary experiments indicate that under certain specific growth conditions, 3D SiC single crystals (100 – 600 Å) of different polytypes can be grown on freestanding amorphous carbon layers, with more or less equal probability of formation for each polytype. On the other hand, under low axial temperature gradients (< 30°C/cm), the SiC epitaxial growth on carbon is amorphous in nature. Also, experimental results that demonstrate two-dimensional single crystal SiC epitaxial growth on an amorphous carbon film deposited on mono-crystalline 6H-SiC wafer, is presented. Experiments performed in our laboratory indicate that monocrystalline SiC growth is possible on amorphous carbon layers upto 0.1 μm thickness.
Selective Etching Of Wide Bandgap Nitrides
Authors: Shul R. J. , Willison C. G. , Bridges M. M. , Han J. , Lee J. W. , Pearton S. J. , Abernathy C. R. , MacKenzie J. D. , Donovan S. M. 
Published: April 2011

AbstractHigh-density plasma etching has been an effective patterning technique for the group-III nitrides due to ion fluxes which are 2 to 4 orders of magnitude higher than more conventional reactive ion etch (RIE) systems. GaN etch rates exceeding 0.68 μm/min have been reported in Cl2/H2/Ar inductively coupled plasmas (ICP) at -280 V dc-bias. Under these conditions, the etch mechanism is dominated by ion bombardment energies which can induce damage and minimize etch selectivity. High selectivity etch processes are often necessary for heterostructure devices which are becoming more prominent as growth techniques improve. In this study, we will report high-density ICP etch rates and selectivities for GaN, AIN, and InN as a function of cathode power, ICP-source power, and chamber pressure. GaN:AIN selectivities > 8:1 were observed in a Cl2/Ar plasma at 10 mTorr pressure, 500 W ICP-source power, and 130 W cathode rf-power, while the GaN:InN selectivity was optimized at ∼ 6.5:1 at 5 mTorr, 500 W ICP-source power, and 130 W cathode rf-power.
Achievement Of Coalesced Oriented Diamond Films On Nickel By Optical Process Control And Methane Enrichment
Authors: Yang P. C. , Wolden C. A. , Liu W. , Schlesser R. , Davis R. F. , Prater J. T. , Sitar Z. 
Published: April 2011

AbstractReal time in-situ laser reflectometry was used to investigate changes in surface morphology observed during the nucleation of oriented diamond on Ni in a hot filament chemical vapor deposition reactor. Characteristic features observed in the intensities of reflected and scattered light were interpreted by comparison with scanning electron micrographs of the diamond seeded substrates quenched at sequential stages of the process. Based on this analysis, a process was developed in which the scattered light signal was used as a steering parameter. Using this process, oriented nucleation and growth of diamond on Ni can be repeatedly achieved. For the purpose of both countering the loss of carbon atoms and to maximize the density of oriented diamond, different concentrations of methane were added during the high temperature annealing stage to find the optimized conditions. It was found that 0.5% methane in the gas phase produced the best degree of orientation and uniformity. Substrates nucleated at these conditions were grown out into coalesced, 30 μm thick films. Both, (100) and (111) oriented films showed a high degree of orientation. Raman spectra obtained from each orientation showed an intense and narrow diamond signature peak with negligible sp2 carbon or background luminescence.
Surface And Interface Study Of Pdcr/Sic Schottky Diode Gas Sensor Annealed At 425°C
Authors: Chen Liang-Yu , Hunter Gary W. , Neudeck Philip G. , Knight Dak 
Published: April 2011

AbstractThe surface and interface properties of a Pd0.9Cr0.1/SiC Schottky diode gas sensor both before and after annealing are investigated using Auger electron spectroscopy (AES), scanning electron spectroscopy (SEM), and energy dispersive spectroscopy (EDS). At room temperature the alloy reacted with SiC and formed PdxSi only in a very narrow interfacial region. After annealing for 250 hours at 425 °C, the surface of Schottky contact area has much less silicon and carbon contamination than that found on the surface of an annealed Pd/SiC structure. PdxSi formed at a broadened interface after annealing, but a significant layer of alloy film is still free of silicon and carbon. The chromium concentration with respect to palladium is quite uniform down to deep interface region. A stable catalytic surface and a clean layer of Pd0.9Cr0.1film are likely responsible for significantly improved device sensitivity.
The Structural Evolution Of Lely Seeds During The Initial Stages Of Sic Sublimation Growth
Authors: Heydemann V. D. , Sanchez E. K. , Rohrer G. S. , Skowronski M. 
Published: April 2011

AbstractThe as-grown surfaces of 6H SiC seed crystals grown by the Lely method have been characterized by visible light microscopy and atomic force microscopy. The surfaces were then used to seed the sublimation growth of SiC at 2300°C, in 650 torr of Ar, with a gradient of 8 °C/cm. Repeated observations of the seed surface structure after predetermined intervals in the growth reactor demonstrated that transport starts at less than 2160 °C and that voids are nucleated by heterogeneous material on the original seed surface. Near these voids, the concentration of unit screw dislocations is increased and these defects migrate during growth. Screw dislocations of opposite sign act as step sources and build mesa structures around the heterogeneous material. After only 10 min at the growth temperature, micropipe/super screw dislocation complexes form in the centers of the mesas, possibly by the migration of unit dislocations to the voids.
High Temperature Characterization Of Ni, W And Al Contacts To 3C-Silicon Carbide Thin Films
Authors: Jacob C , Pirouz P , Kuo H-I , Mehregany M 
Published: April 2011

AbstractWith the current availability of large-area 3C-SiC films, it is imperative that stable high temperature contacts be developed for high power devices. By comparing the existing data in the literature, we demonstrate that the contact behavior on each of the different polytypes of SiC will vary significantly. In particular, we demonstrate this for 6H-SiC and 3C-SiC. The interface slope parameter, S, which is a measure of the Fermi-level pinning in each system varies between 0.4–0.5 on 6H-SiC, while it is 0.6 on 3C-SiC. This implies that the barrier heights of contacts to 3C-SiC will vary more significantly with the choice of metal than for 6H-SiC.Aluminum, nickel and tungsten were deposited on 3C-SiC films and their specific contact resistance measured using the circular TLM method. High temperature measurements (up to 400°C) were performed to determine the behavior of these contacts at operational temperatures. Aluminum was used primarily as a baseline for comparison since it melts at 660°C and cannot be used for very high temperature contacts. The specific contact resistance (ρc) for nickel at room temperature was 5 × 10−4 Ω-cm2, but increased with temperature to a value of 1.5 × 10−3 Ω-cm2 at 400°C. Tungsten had a higher room temperature × 10−3 Ω-cm2, which remained relatively constant with increasing temperature up to 400°C. This is related to the fact that there is hardly any reaction between tungsten and silicon carbide even up to 900°C, whereas nickel almost completely reacts with SiC by that temperature. Contact resistance measurements were also performed on samples that were annealed at 500°C.
Dielectrics for GaN Based MIS-Diodes
Authors: Ren F. , Abernathy C. R. , MacKenzie J. D. , Gila B. P. , Pearton S. J. , Hong M. , Macos M. , Schurman M. J. , Baca A. G , Shul R. J. 
Published: April 2011

AbstractGaN MIS diodes were demonstrated utilizing AIN and Ga2O3(Gd2O3) as insulators. A 345 Åof AIN was grown on the MOCVD grown n-GaN in a MOMBE system using trimethylamine alane as Al precursor and nitrogen generated from a wavemat ECR N2 plasma. For the Ga2O3(Gd2O3) growth, a multi-MBE chamber was used and a 195 Å oxide is E-beam evaporated from a single crystal source of Ga5Gd3O12. The forward breakdown voltage of AlN and Ga2O3( Gd2O3) diodes are 5V and 6V, respectively, which are significantly improved from ˜1.2 V of schottky contact. From the C-V measurements, both kinds of diodes showed good charge modulation from ccumulation to depletion at different frequencies. The insulator/GaN interface roughness and the thickness of the insulator were measured with x-ray reflectivity.
Heat Spreader Characteristics Of Multilayer Diamond Films For High Frequency Power Devices
Authors: Ramaswami B. , Jagannadham K. 
Published: April 2011

AbstractSingle layer diamond and multilayer diamond films consisting of diamond and aluminum nitride are deposited on molybdenum and silicon nitride substrates. Silicon or GaAs device wafers and the diamond substrates are prepared by metallization and bonded using gold-tin eutectic solder. Results of characterization of the bond by thermal cycling, scanning electron microscopy of the cross-section samples and X-ray mapping of the distribution of different elements are presented. Advantages of use of multilayer diamond composite heat spreaders in power semiconductor devices are discussed.
Photovoltaic Properties of Fullerene (C60) Thin films
Authors: Katz E. A. , Faiman D. , Goren S. , Shtutina S. , Shames A. , Mishori B. , Shapira Yoram 
Published: April 2011

AbstractThe crystalline structure, Electron Paramagnetic Resonance and Surface Photovoltage (SPV) spectra of C60 thin films and the photovoltaic properties of C60/Ag and C60/Si interfaces are reported. The SPV spectra of C60 films, C60/Ag and C60/Si interfaces are presented and analyzed on the basis of a model of C60 film electron structure including mobility gap, band tails extending into the gap and two deep level states in the gap. I-V characteristics of the C60/Ag and the C60/P-Si interfaces were measured. Both device structures are shown to exhibit rectifying behavior in the dark and photovoltaic properties. The solar cell parameters are presented.
Surface Modification of Cu(In,Ga)Se2 Thin Films During Aqueous Oxidation Etch
Authors: Canava B. , Guillemoles J. F. , Lincot D. , Vedel J. , Ardelean H. , Malengreau F. 
Published: April 2011

AbstractThe control of the barrier height at the Cu(In,Ga)Se2(CIGS)/CdS interface, via the chemical state of the CIGS surface, is a key to improve solar cell performances. In this paper chemical modifications have been achieved by the electrochemical method, by varying both the pH of the solution and the applied potential. It is shown that the potential for electrochemical oxidation depends on the pH, in good agreement with the thermodynamic predictions. The resulting surface composition of CIGS, analyzed by XPS, also depends on the pH. Contact Potential Differences (CPD) and Surface Photovoltage (SPV) measurements show that the electronic properties of the CIGS surface are modified. The important result is that the oxidation leads to the formation of permanent positive surface charges, which increase the band bending up to 0.20 V in a direction favorable for the solar cell performances.
Characterization of Cu(In,Ga)Se2/Mo Interface in CIGS Solar Cells
Authors: Nishiwaki S. , Kohara N. , Negami T. , Nishitani M. , Wada T. 
Published: April 2011

AbstractThe interface between a Cu(In,Ga)Se2 (CIGS) and an underlying Mo layer was studied by X-ray diffraction and high resolution transmission electron microscopy. The CIGS layer was deposited onto Mo coated soda-lime glass using the “3-stage” process. A MoSe2 layer found to form at the CIGS/Mo interface during the 2nd stage of the “3-stage” process. The thickness of the MoSe2 layer depended on the substrate temperature used for CIGS film deposition as well as the Na content of the CIGS and/or Mo layers. For higher substrate temperatures, thicker MoSe2 layers were observed. The Na in the CIGS and/or Mo layer is felt to assist in the formation of MoSe2. Current-Voltage measurements of the heterojunction formed by the CIGS/Mo interface were ohmic even at low temperature. The role of the MoSe2 layer in high efficiency CIGS solar cells is discussed.