bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of N2 Plasma Treatments on Dry Etch Damage in n- and p-type GaN
Authors: Kent D.G. , Lee K.P. , Zhang A.P. , Luo B. , Overberg M.E. , Abernathy C.R. , Ren F. , Mackenzie K.D. , Pearton S.J. , Nakagawa Y. 
Published: April 2011

ABSTRACTThe extent of damage recovery by N2 plasma treatment of previously damaged n- and p-GaN has been examined using current-voltage (I-V) characteristics from Schottky diodes. There are two contributions to the observed improvement in the I-V characteristics, namely a simple annealing effect and also a chemical effect from reactive nitrogen. However the N2 plasma treatment does not fully restore the initial electrical properties of the near-surface region.
Microstructure of GaN Grown on (1120) Sapphire
Authors: Ruterana P. , Wickenden A. E. , Twigg M. E. , Koleske D.D. , Henry R. L. , Tottereau O. 
Published: April 2011

ABSTRACTMost of the work done on GaN has taken into account layers grown on the (0001) sapphire. However one would expect the growth on (1120) to lead to different structural defects. As has been shown, in one direction, the mismatch is rather small. In this work, we have carried out structural analysis of layers and interfacial relationship. Inside the layers, the density of defects is comparable to that found conventionally in layers grown on top of (0001) sapphire. The growth mode is also mosaic with a grain size of a few microns. One interesting result is the interface structure, which differs from conventional growth where a flat or stepped interface is formed with a large distance between steps. In this case, the interface is found to be rough at the atomic scale so that this roughness has a random distribution. Moreover, the misfit dislocation spacing is 1nm which is only half the dislocation spacing found in GaN growth on (0001) sapphire.
Fabrication of GaN layer with Low Dislocation Density using Facet controlled ELO technique
Authors: Miyake H. , Mizutani H. , Hiramatsu K. , Iyechika Y. , Honda Y. , Maeda T. 
Published: April 2011

ABSTRACTGaN layers with low dislocation density have been fabricated be means of facet-controlled epitaxial lateral overgrowth (FACELO) via low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). The distribution of the dislocations in FACELO GaN was inspected by observation of InGaN growth pits. For FACELO with {11-20} facets as the first step, the dislocations concentrate only in the window region. For FACELO with {11-22} facets as the first step, the dislocations exist only in the coalescence region. The double FACELO, which was FACELO with {11-20} on FACELO with {11-22}, was demonstrated and dislocation density of less than 105 cm−2 was achieved.
Effect of Thermal Annealing on the Photoluminescence Properties of a GaInNAs/GaAs Single Quantum Well
Authors: Grenouillet Laurent , Bru-Chevallier Catherine , Guillot Gérard , Gilet Philippe , Ballet Philippe , Duvaut Philippe , Chenevas-Paule Andrè , Million Alain 
Published: April 2011

ABSTRACTWe report on the effect of thermal annealing on the photoluminescence properties of a Ga0.65In0.35N0.02As0.98/GaAs single quantum well. Thermal annealing is shown to decrease the strong nitrogen-induced localization effects observed at low temperatures and to reduce the full width at half maximum of the emission peak. It also induces a strong blue shift of the emission peak energy, which is thought not to arise from an In-Ga interdiffusion alone, as it is much larger than in a nitrogen-free reference single quantum well.
Photoluminescence Studies of p-type GaN:Mg Co-doped with Oxygen
Authors: Korotkov R. Y. , Gregie J. M. , Wessels B. W. 
Published: April 2011

ABSTRACTThe low temperature photoluminescence (PL) of Mg-doped GaN co-doped with oxygen is investigated. Two PL bands are observed at low temperature at 2.5 and 2.8 eV in the p-type oxygen co-doped samples. Both the 2.5 eV and 2.8 eV bands are attributed to donor-acceptor (DA) transitions involving deep donors of different origin and a shallow MgGa acceptor. The integrated intensity of the 2.8 eV band in p-type GaN decreases as the oxygen partial pressure is increased. The decrease is attributed to reduced compensation by deep native donors. The two bands are not formed in n-type (n > 1019 cm−3) GaN:Mg over-doped with oxygen indicating that the deep donors responsible for these transitions have high formation energies in n-type material.
Group III-Nitride Based VCSEL for Applications at the Wavelength of 400nm
Authors: Linnik M. , Christou A. 
Published: April 2011

ABSTRACTShort wavelength Vertical Cavity Surface Emitting Laser based on the group III nitrides, GaN, AlN, InN, and their ternary alloys is reported. Optical properties such as band gap and index of refraction of the nitride binary compound were calculated based on the fitting of the experimental data and the first principle calculations. The ternary alloy optical properties were determined in the same manner but based on the binary compound data. The active region containing InGaN strained multiple quantum wells is formed between two Distributed Bragg Reflectors. GaInN/AlN material systems are shown to be the most suitable for highly reflective Bragg mirrors with minimized number of layers. LiGaO2 substrate is proposed for GaN growth due to its small lattice mismatch with GaN (about 0.9%) and its ability to provide a good thermal matching between the two materials. We report VCSEL calculations on threshold current and emission spectra.
A Generalized Roosbroeck-Schockley Relation for III-Nitrides in Far-from-Equilibrium Conditions
Authors: Vasconcellos A. R. , Luzzi R. , Rodríguez C. G. , Freire V. N. , Costa A. P. da 
Published: April 2011

ABSTRACTWe consider the behavior of the absorption coefficient and luminescence spectrum in the steady state when III-nitrides semiconductors (compounds GaN, AlN, and InN) are in far-fromequilibrium conditions created by an electric field. We analyze the high frequency part of the spectra obtaining a generalization of the Roosbroeck-Schockley relation, δRS(ω, EF), the ratio between the frequency dependent luminescence I(ω) and the absorption coefficient α(ω), for nonequilibrium conditions which are dependent on the electric field intensity EF. We show that the carrier's temperature within a small error is proportional to d ln[δRS(ω, EF)]/dω.
High electron mobility in free-standing GaN substrates
Authors: Saxler A. , Look D. C. , Elhamri S. , Sizelove J. , Cull D. , Mitchel W. C. , Callahan M. , Bliss D. , Bouthillette L. , Wang Sheng-Qi , Sung C. M. , Park S. S. , Lee K. Y. 
Published: April 2011

ABSTRACTHigh peak electron mobilities were observed in free-standing c-plane GaN substrates. Two layers, a low mobility degenerate layer and a high mobility bulk layer, were present in these samples. The carrier concentrations and mobilities for the layers were extracted using two methods: 1) magnetic field dependent Hall effect analysis and 2) a simple two carrier model with the assumption that one of the layers is degenerate. In addition, measurements were performed after etching away the degenerate layer. The mobility of the bulk layer is found to peak at nearly 8000 cm2/Vs at 60K using the magnetic field dependent Hall effect data. Record room temperature mobility for bulk GaN of 1190 cm2/V s was measured.
Phonon Lifetimes and Phonon Decay Channels in Single Crystalline Bulk Aluminum Nitride
Authors: Kuball M. , Hayes J.M. , Shi Ying , Edgar J.H. 
Published: April 2011

ABSTRACTWe report on the Raman analysis of the phonon lifetimes and phonon decay channels of the A1(LO), E1(LO) and E2(high) phonons of single crystalline bulk AlN grown by the sublimationrecondensation method. The temperature dependence of the phonon lifetimes was investigated from 10K to 1275K. Our experimental results show that amongst the various possible decay channels, the A1(LO) phonons of AlN decay primarily into two phonons of equal energy (Klemens model), most likely longitudinal-acoustic (LA) phonons. AlN is therefore in great contrast to GaN, where a symmetric decay of the A1(LO) phonons is not possible due to a large energy gap between the acoustic and optical phonon branches. For the E2(high) phonon, we find an asymmetric phonon decay into a high-energy and a low-energy phonon. Possible decay channels of the E2(high) phonon include combinations of E2(low) and acoustic phonons. For the E1(LO) phonons, the temperature dependence of the phonon lifetime is consistent with a symmetric phonon decay. Phonon lifetimes of the A1(LO), the E1(LO) and the E2(high) phonon of 0.75ps, 1.2ps and 2.9ps, respectively, were measured at 10K.
Smoothening of (001) and (111) Cu films epitaxially grown on Si substrates
Authors: Lukaszew Rosa Alejandra , Uher Ctirad , Clarke Roy 
Published: April 2011

AbstractWe report an in-situ study of the MBE growth of Cu films on hydrogen-terminated Si (001) and (7×7) reconstructed Si(111) substrates. Using correlated RHEED and STM data, we find a dramatic smoothing of epitaxial Cu(001) surfaces by annealing the as- grown films in the 120-160oC temperature range and somewhat less so for the Cu (111) films. Our measurements reveal a lower activation energy (0.40 ± 0.04 eV) for inter- terrace mass transport in Cu(001) than for Cu(111) (1.10 ± 0.03 eV) the former possibly influenced by the presence of hydrogen. Scaling analysis of the subsequent Cu growth on the annealed smooth surfaces yields a coarsening exponent of 1/4 for the (001) oriented films while this exponent is 1/3 for the (111) films, providing for the first time experimental data for the same system in these two orientations.
Mechanism of Interfacial Coarsening in Molecular Beam Epitaxy Growth on (001) Surfaces
Authors: Golubovic Leonardo , Moldovan Dorel 
Published: April 2011

AbstractWe theoretically address epitaxial growth on (001) crystalline surfaces symmetry, in the regime when pyramids are formed across the growing interface due to Schwoebel step-edge barriers. We develop a kinetic scaling theory that analytically explains numerous experiments and simulations suggesting that pyramid size grows, via coarsening, as a fourth root of the deposition time. Pyramid dynamics is elucidated in terms of pyramid edges that form a growing self-organized square lattice across the growing interface. The edge lattice of pyramids is disordered by topological defects that are characterized here as dislocations. We show that pyramid coarsening is mediated by climb-motion of the dislocations of the edge lattice.
RHEED Observation of Tin Atomic Chains Formation on Vicinal Gallium Arsenide Plane
Authors: Senichkin Aleksey , Bugaev Aleksandr , Mokerov Vladimir 
Published: April 2011

AbstractIn the present work by means of measurements of RHEED intensity the research of the arrangement of tin atoms on vicinal surfaces of GaAs crystals was carried out. The orientation of crystals was close to (001). The intensity of diffracted electrons was measured in different points of the diffraction picture to reveal the arrangement of tin atoms on terraces or on edges of terraces. It was shown that tin atoms may decorate edges of terraces and thus form chains. Concentrations of tin atoms located on terraces and their edges were established. It was revealed, that tin atoms decorate edges of terraces only at rather high temperatures of a substrate.
A Hydrogen-Bonding Based Approach to Fabricate Polymer/Inorganic Nanoparticle Multilayer Film
Authors: Hao Encai , Lian Tianquan 
Published: April 2011

AbstractA new hydrogen-bonding based route for layer-by-layer fabrication of polymer/inorganic nanoparticle multilayer thin films was developed. Surface modification of inorganic nanoparticles can provide functional groups on the particle surface, e.g. pyridine, carboxyl, and flavin. A polymer/inorganic nanoparticle multilayer film can be fabricated in a layer-by-layer manner using the hydrogen-bonding interaction between the functional groups on the surface of nanoparticles and polymers. The multilayer buildup was monitored by UV-visible spectroscopy, which showed a linear increase of the film absorbance with the number of adsorbed nanoparticle layers. FTIR spectroscopy was used to verify hydrogen bonding between polymer and nanoparticles, which is believed to be the driving force for the formation of polymer/nanoparticle multilayer thin films.
Fabrication of Multilayer Films Using a Spinning Process
Authors: Cho Jinhan , Char Kookheon , Hong Jong-Dal , Lee Ki-Bong 
Published: April 2011

AbstractWe introduce a method to build up organic/organic and organic/inorganic multilayer films composed of cationic poly(allylamine hydrochloride) (PAH) and negatively charged poly(sodium 4-styrenesulfonate) (PSS) or inorganic cadmium sulfide (CdS) nanoparticles using a spinning process. Since the deposition of each layer is made at a high spinning speed, the adsorption time for the formation of a homogeneous thin layer takes only 8 to 15 seconds. The adsorbed film thickness per bilayer can be easily controlled from about 5Å to 40Å by varying the spinning speed (Ω) and the mole concentration of polyelectrolytes. We also demonstrated with X-ray reflectivity that the alternating organic/inorganic ultrathin films fabricated by the spin SA process retain highly ordered internal structure in comparison with those prepared by the conventional SA process.
Monte Carlo Simulation of Vapour Deposition of Nonstoichiometric Amorphous Silica
Authors: Burlakov V. M. , Tsukahara Y. , Briggs G. A. D. , Sutton A. P. 
Published: April 2011

AbstractMonte Carlo simulation of deposition of nonstoichiometric amorphous SiOx nanolayers from vapor phase onto a polymer surface is reported. The model developed is based on the network properties of silica and takes into account dangling bonds arising during the real process of deposition. The model is validated via comparison of the radial- and bond angle distribution functions for the simulated Si and SiO2 structures with those obtained from experiment for bulk materials. Porosity of the simulated amorphous layer is characterized by the relative volume of pores and the ratio of the pore surfaces to the pore volume. We found that porosity strongly depends on nucleation sites density (NSD) on the polymer substrate. At NSD lower than 1 nm−2 the porosity may reach as much as 30% of the layer volume, while at NSD higher than 4 nm−2 it decreases down to 3-7%. Possible implications of the obtained results are discussed.
Elastic Properties of Diamond-Like Amorphous Carbon Films Grown by Computer Simulation of Ion-Beam Deposition Process
Authors: Belov A.Yu. , Jäger H.U. 
Published: April 2011

AbstractAtomic-scale calculations were performed for the first time to investigate mechanical properties of amorphous carbon films grown by a realistic simulation of ion-beam deposition. The simulated films have a thickness of a few nanometers and reproduce the main structural features of real films, with the bulk content of sp3 bonded atoms varying from 35 to 95%, depending on the ion energy (E = 20-80 eV). Employing empirical interatomic potentials for carbon, the average bulk stresses as well as the atomic-level stress distributions were calculated and analysed. The bulk stresses were found to depend not only on the ion energy, but also on the film quality, in particular, on such structural inhomogeneities as local fluctuations of the sp3 fraction with the depth. The local variation of the bulk stress from the average value considerably increases as the local content of sp2 bonded atoms increases. Elastic constants of amorphous carbon films were also computed using the method of inner elastic constants, which allows for the stress dependence of elastic constants to be analysed. The variation of Young's modulus as a function of the lateral bulk stress in an amorphous film is demonstrated.
STM characterization of Cu thin films grown by direct ion deposition
Authors: Pomeroy Joshua M. , Couture Aaron , Jacobsen Joachim , Hill Colin C. , Sethna James P. , Cooper Barbara H. , Brock Joel D. 
Published: April 2011

AbstractIn certain cases, the incidence energy of constituent atoms activates an atomistic insertion mechanism, which decreases the surface roughness of metal thin films. In an effort to probe this effect, homoepitaxial copper films were grown using a mass/energy selected direct ion deposition technique that allows precise control of the incidence energy. Surface roughness is measured using a Scanning Tunneling Microscope (STM) within the same UHV surface analysis system. The activation of the insertion mechanism near 20 eV triggers smoother crystal growth. The beneficial effects begin to be obscured by adatom/vacancy creation near 30 eV. A sophisticated Kinetic Monte Carlo/Molecular Dynamics (KMC-MD) model supports this interpretation.
Synthesis and Crystal Chemistry of New Transition Metal Tellurium Oxides in Compounds Containing Lead and Barium
Authors: Wedel Boris , Sugiyama Katsumasa , Itagaki Kimio , Müller-Buschbaum Hanskarl 
Published: April 2011

ABSTRACTDuring the past decades the solid state chemistry of tellurium oxides has been enriched by a series of quaternary metallates. Interest attaches not only to the chemical and physical properties of these compounds, but also to their structure, which have been studied by modern methods. The partial similarity of earth alkaline metals and lead in solid state chemistry and their relationships in oxides opens a wide field of investigations. Eight new compounds in the systems Ba-M-Te-O (M= Nb, Ta) and Pb-M-Te-O (M = Mn, Ni, Cu, Zn) were prepared and structurally characterized: Ba2Nb2TeO10, Ba2M6Te2O21 (M = Nb, Ta) and the lead compounds PbMnTeO3, Pb3Ni4.5Te2.5O15, PbCu3TeO7, PbZn4SiTeO10 and the mixed compound PbMn2Ni6Te3O18. The structures of all compounds are based on frameworks of edge and corner sharing oxygen octahedra of the transition metal and the tellurium. Various different channel structures were observed and distinguished. The compounds were prepared by heating from mixtures of the oxides, and the single crystals were grown by flux method or solid state reactions on air. The synthesis conditions were modified to obtained microcrystalline material for purification and structural characterizations, which were carried out using a variety of tools including powder diffraction data and refinements of X-ray data. Relationships between lead transition metal tellurium oxides and the earth alkaline transition metals tellurium oxides are compared.
Resistive Anomaly Relevant to Nd Moments in the Antiferromagnetic Phase of the Bandwidth-Controlled Manganites
Authors: Kuwahara H. , Noda K. , Kawasaki R. 
Published: April 2011

ABSTRACTWe have investigated the electronic and magnetic properties of (Nd1−ySmy)0.45Sr0.55MnO3(0≤y≤1) crystals, in which one-electron bandwidth (W ) is systematically decreased from the parent compound (y=0) with increase of y. We have found remarkable magnetic phase transition concerning the change of rare-earth (RE) moments in low temperatures below 25 K. The subtle drop in resistivity superimposed upon the spin-valve like magnetoresistance (MR) was observed for the isothermal MR measurements, e.g. δρ(H)|ρ(H')≍4.7% at 3.5 T and 4 K. The phase transition fields corresponding to these concomitant magnetic and resistive changes monotonically decrease with temperature and disappear above ∼25 K. It turned out that the resistive drop is due to the field-induced increase of magnetic moments ofRE ions from magnetization measurements. The field-induced phase transition from the small moment state to the large one in RE ions can be explained in terms of energy level crossing between the crystal-field-split J multiplets by the Zeeman effect.
Competitive Adsorption of O2 and H2O at the Neutral and Defective SnO2 (110) Surface
Authors: Slater Ben , Catlow C. Richard A. , Williams David E. , Stoneham A. Marshall 
Published: April 2011

ABSTRACTUsing first principles techniques we have examined the relative physisorption/chemisorption energetics of neutral molecular water and oxygen at the most thermodynamically stable surface (110) of tin dioxide. We find that water binds more strongly to the perfect surface at 5 co- ordinate tin sites than oxygen. However, binding of both water and oxygen at bridging oxygen vacancies in the defective surface is comparable. In the context of gas-sensing behaviour at moderate temperatures (∼300K), we propose that the Mars and van Krevelen [1] re-oxidation reaction will slow when the partial pressure of water is high, since the number of favourable adsorption sites will effectively decrease. In addition, one would expect that the surface conductivity will increase, since the re-oxidation reaction will be hindered.
Towards Stabilized 10% Efficiency of Large-Area (> 5000cm2) a-Si/a-SiGe Tandem Solar Cells using High-Rate Deposition
Authors: Okamoto Shingo , Terakawa Akira , Maruyama Eiji , Shinohara Wataru , Tanaka Makoto , Kiyama Seiichi 
Published: April 2011

ABSTRACTThis paper reviews recent progress in large-area a-Si/a-SiGe tandem solar cells in Sanyo. Much effort has been devoted to increasing both the stabilized efficiency and the process throughput. A key issue in increasing the stabilized efficiency is thinner i-layer structure with an improved optical confinement effect. High-rate deposition of the i-layers has been investigated using rf (13.56MHz) plasma-CVD method while keeping the substrate temperature below 200 °C. A high photosensitivity of 106 of a-Si:H films maintain up to the deposition rate (Rd) of 15 Å/s by optimizing hydrogen dilution and other deposition conditions. It is of great importance to utilize the effect of hydrogen dilution which can reduce the incorporation of excess hydrogen in the films. The world's highest conversion efficiency of 11.2% has been achieved for a large-area (8252cm2) a-Si/a-SiGe tandem by combining the optimized hydrogen dilution and other solar cell related technologies.
Defect Creation by Electron Beam Irradiation in Amorphous Silicon Nitride Films Compared with That by Light Soaking
Authors: Shimizu Tatsuo , Kawashima Yuji , Kumeda Minoru 
Published: April 2011

ABSTRACTDefect creation by electron beam irradiation is compared with that by light soaking in a-Si1-xNx:H films. For the film with x=0.06, the ESR spin density increases by 20-keV electron beam irradiation without changes in the g-value. However, for the film with x=0.47, the ESR spin density increases with accompanying the decrease in the g-value from 2.0042 to 2.0034. The decrease in the g-value can be explained by increasing number of N atoms at the backbond site of the Si atom having the dangling bond. Light soakings does not change the g-value of the ESR signals of the films.
Structural Properties of Microcrystalline Si Solar Cells
Authors: Luysberg M. , Scholten C. , Houben L. , Carius R. , Finger F. , Vetterl O. 
Published: April 2011

ABSTRACTThe structural properties of nip-µc-Si:H solar cells are investigated by transmission electron microscopy, X-ray diffraction and Raman spectroscopy. Different structural compositions are obtained by variation of the gas mixture during preparation by plasma enhanced chemical vapour deposition. Nucleation and growth of the n-layer onto textured TCO substrate was found to be similar to the growth on glass substrates. The growth of the i-layer follows a local epitaxy. This implies that the structure of the n-layer is of special importance regarding the control of the microstructure in microcrystalline Si nip solar cells.