bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of GaN Films on Sapphire by Cathodoluminescence
Authors: Chao L.-L. , Cargill G. S. , Kothandaraman C. 
Published: April 2011

ABSTRACTCathodoluminescence (CL) spectroscopy and microscopy were used to study the luminescent properties of a variety of GaN films, both Si-doped and unintentionally-doped, grown on sapphire substrates. A narrow and intense near band-edge emission was found in the CL spectrum of each film examined, and deep-level emission was also observed for some of the films. The luminescence efficiency of near band-edge emission increased with a faster rate than that of deep-level emission when the pumping current was increased. Spatial nonuniformities of luminescence were observed in monochromatic CL microscopy, and microstructures were observed in scanning electron microscopy. No correlations between luminescence features and microstructural features were seen. Degradation of near band-edge luminescence was observed, accompanied by growth of deep-level emission.
Initial Growth Stage of AlGaN Grown Directly on (0001) 6H-SiC by MOVPE
Authors: Horino K. , Kuramata A. , Tanahashi T. 
Published: April 2011

ABSTRACTWe investigated the growth process of AlGaN films grown directly on 6H-SiC (0001) substrates by metalorganic vapor phase epitaxy (MOVPE). We focused on the initial growth stage to clarify the mechanism of nitride growth on SiC. From Energy Dispersive X-ray (EDX) analysis we found that an Al-rich region generated naturally at the AlGaN/SiC interface. We also found that Al flux determined the density of grain which generated during the initial growth stage, and this grain density reflected the surface morphology.
Optical Signature of the GaN (1010) Surface
Authors: Noguez C. , Esquivel-Sirvent R. , Alfonso D. R. , Ulloa S. E. , Drabold D. A. 
Published: April 2011

ABSTRACTWe present a theoretical study of the optical properties of the GaN (1010) surface. We employed a semi-empirical tight-binding method to calculate the surface electronic structure. The parameters were adjusted to reproduce the correct band structure of the bulk wurzite GaN. These parameters were interpolated to the surface using Harrison’s rule. From the surface electronic structure the surface dielectric response was obtained. The dielectric response is analized in terms of surface-surface, and surface-bulk electronic transitions.
Stability and Band Offsets of SiC/GaN, SiC/AlN, and AlN/GaN Heterostructures
Authors: Majewski J. A. , Städele M. , Vogl P. 
Published: April 2011

ABSTRACTWe present first-principles calculations of structural and electronic properties of heterova-lent SiC/GaN, SiC/AIN, and isovalent AIN/GaN heterostructures that are grown pseudo-morphically on (001) or (110) SiC substrates. For the polar interfaces, we have investigated reconstructed stoichiometric interfaces consisting of one and two mixed layers with lateral c(2 × 2), 2 × 1, 1 × 2, and 2 × 2 arrangements. The preferred bonding configurations of the reconstructed interfaces are found to be Si-N and Ga-C. With respect to vacuum, the valence band maximum is found to be highest in SiC and lowest in A1N. In these systems, the valence band offsets deviate substantially from the transitivity rule and depend sensitively on the microscopic details of the interface geometry. The SiC/AIN and AIN/GaN heterostructures are predicted to be of type I, whereas SiC/GaN heterostructure can be of type I or II.
Chlorine-Based Plasma Etching of GaN
Authors: Shul R. J. , Briggs R. D. , Pearton S. J. , Vartuli C. B. , Abernathy C. R. , Lee J. W. , Constantine C. , Barratt C. 
Published: April 2011

ABSTRACTThe wide band gap group-III nitride materials continue to generate interest in the semiconductor community with the fabrication of green, blue, and ultraviolet light emitting diodes (LEDs), blue lasers, and high temperature transistors. Realization of more advanced devices requires pattern transfer processes which are well controlled, smooth, highly anisotropic and have etch rates exceeding 0.5 μm/min. The utilization of high-density chlorine-based plasmas including electron cyclotron resonance (ECR) and inductively coupled plasma (ICP) systems has resulted in improved etch quality of the group-III nitrides over more conventional reactive ion etch (RIE) systems.
Ion Implantation and Annealing Studies in III–V Nitrides
Authors: Zolper J. C. , Pearton S. J. , Williams J. S. , Tan H. H. , Karlicek R. J. , Stall R. A. 
Published: April 2011

ABSTRACTIon implantation doping and isolation is expected to play an enabling role for the realization of advanced Ill-Nitride based devices. In fact, implantation has already been used to demonstrate n- and p-type doping of GaN with Si and Mg or Ca, respectively, as well as to fabricate the first GaN junction field effect transistor.1-4 Although these initial implantation studies demonstrated the feasibility of this technique for the Ill-Nitride materials, further work is needed to realize its full potential.After reviewing some of the initial studies in this field, we present new results for improved annealing sequences and defect studies in GaN. First, sputtered A1N is shown by electrical characterization of Schottky and Ohmic contacts to be an effective encapsulant of GaN during the 1100 °C implant activation anneal. The A1N suppresses N-loss from the GaN surface and the formation of a degenerate n+-surface region that would prohibit Schottky barrier formation after the implant activation anneal. Second, we examine the nature of the defect generation and annealing sequence following implantation using both Rutherford Backscattering (RBS) and Hall characterization. We show that for a Si-dose of l × l016 cm-2 50% electrical donor activation is achieved despite a significant amount of residual implantation-induced damage in the material.
Molecular Dynamic Simulations of Semiconductor Clusters
Authors: Dubey Girlta S. , Gumbs Godfrey 
Published: April 2011

AbstractMolecular dynamics simulations are carried out for silicon clusters to analyze the effect of heating and cooling on their structural properties. The calculations are based on the Kaxiras and Pandey potential which has been derived from a microscopic calculation with the density functional method. Results for the cluster formation are presented for different rates of cooling and heating. Our simulations clearly show the dependence of the patterns on the cooling and heating rates as well as the way in which these clusters evolve. Our results indicate that the structures are most stable when the rate of loss of thermal energy is slow and the potential energy is lowest.
Porous Microcrystalline Silicon Solar Cells
Authors: Duttagupta S. P. , Kurinec S. K. , Fauchet P. M. 
Published: April 2011

AbstractWe report the fabrication of photovoltaic devices by the anodization of microcrystalline silicon films on single crystal silicon substrates. The porosity of the films was varied from 20% to 60% by changing the anodization conditions. An unetched μc-Si based device was used for reference. The influence of the porosity on the series resistance (Rs), the reflectance, and the spectral response of the devices was studied in detail. In order to determine Rs, the current-voltage characteristics were analyzed, both in the dark and under illumination. We observed that the value of Rs increased from 3.1 Ω to 97 Ω and the value of the reflectance decreased from 24% to 7% when the porosity increased from 20% to 60%. Initially, an optimum device performance (fill factor of 0.53 and efficiency of 7.2%) was achieved for a porosity of 40%, which was about a 40% improvement as compared to the reference (unetched) μc-si based device. Due to a further reduction in Rs by using an intermediate ITO layer and a superior grid-contact architecture, a device efficiency of 10% has been recently achieved.
Electroluminescence Device Perspectives of Si+-Implanted SiO2
Authors: Kozlowski F. , Porteanu H. E. , Petrova-Koch V. , Koch F. 
Published: April 2011

AbstractThermal oxide layers on Si which have been implanted with Si conduct electrical current and emit light. The electroluminescence effect (EL) has an efficiency which is comparable to the best values that have been reported for the porous Si based devices. Generally, the EL spectrum differs substantially from the photoexcited luminescence. It is linked with that excited by external high energy electrons in cathodoluminescence (CL) experiments. We suggest to consider the effect as internal CL. Based on studies of transport and EL characteristic we evaluate the possibilities of an electroluminescent device based on such layers.
Electroluminescent Devices Based on Zero- and One- Dimensional Silicon Structures
Authors: Nassiopoulos A. G. , Photopoulos P. , Ioannou-Sougleridis V. , Grigoropoulos S. , Papadimitriou D. 
Published: April 2011

AbstractStable solid state electroluminescent devices, based on one- and two- dimensional silicon structures were fabricated. One- dimensional structures were in the form of silicon nanopillars on a silicon substrate, fabricated by using lithography and etching techniques. Isolation and planarization of nanopillars was made by using polymethyl methacrylate (PMMA), which is a non conducting polymer, totally transparent in the visible region. Gold (Au) was used as top contact metal and the back ohmic contact was based on aluminum. Zero-dimensional structures were in the form of silicon nanocrystallites, deposited by low pressure chemical vapour deposition (LPCVD) on a thin SiO2 layer, thermally grown on silicon. Gold and aluminum were also used as contact metals. In both cases the devices showed stable electroluminescence at room temperature, visible with the naked eye. Devices based on nanocrystallites showed more uniform emission. The onset of light emission was between 5 and 7 Volts. The devices were checked for several hours of continuous operation and no degradation was observed.
Preparation and Characterization of the Active Layer for an Led Based on Oxidized Porous Silicon
Authors: Tsybeskov L. , Hiirschman K. D. , Moore L. F. , Fauchet P. M. , Calcott P. D. J. 
Published: April 2011

AbstractWe have studied the photoluminescence (PL) in oxidized porous silicon (PSi), prepared from anodized crystalline Si followed by annealing at temperatures ranging from 700 to 1000°C. It has been found that two PL bands with spectral peaks at 1.6 e V (near-IR band) and near 2 eV (red band) exist with a strong dependence on preparation (annealing) conditions. Recent experimental results show a correlation between the intensity of the near-IR band and the level of leakage current in the diode-like structure. The suppression of the near-IR emission results in improved carrier transport, and the enhancement of the red band emission maximizes the electroluminescence (EL) efficiency. The PL study of thermally oxidized PSi indicates different recombination mechanisms. The red PL band is associated with a mechanism similar to band-tail-recombination within the quasi-bandgap of Si nanograins, whereas the near infra-red PL is associated with recombination via defect centers. These mechanisms will be discussed.
Substrate-Surface Effect on Initial Growth Process of Microcrystalline Silicon Films
Authors: Ikuta K. , Park J. W. , Kuo L. H. , Yasuda T. , Yamasaki S. , Tanaka K. 
Published: April 2011

AbstractInitial growth processes of hydrogenated microcrystalline silicon (μc-Si:H) films have been investigated by scanning tunneling microscopy (STM), high-resolution transmission electron microscopy (HRTEM), and reflection high energy electron diffraction (RHEED). The μc-Si:H films were prepared by plasma enhanced chemical vapor deposition (PECVD) on H-terminated Si(111) and plasma-oxidized SiO2/Si(111) surfaces that were made atomically-flat by a careful wet processing. On H-terminated Si(111) the initial growth was epitaxial as evidenced by HRTEM and RHEED, while on SiO2/Si(111) the initial process was nucleation of amorphous Si followed by formation of randomly oriented μc-Si:H structure. STM observation revealed that, on both H-terminated and SiO2-terminated surfaces, initial growth processes proceed through the nucleation-and-coalescence mechanism.
Theory of Pressure Effects on Silicon Nanocrystallites
Authors: Allan G. , Delerue C. , Lannoo M. 
Published: April 2011

AbstractPressure effects on silicon nanocrystallites are calculated using semi-empirical tight-binding and ab-initio local density calculations. Using the confinement model in porous silicon a red shift of the luminescence energy with increasing pressure is obtained. Quantum confinement in BC8 phase silicon nanocrystallites obtained after release of high pressure are also studied. It increases the cluster gap and also enhances the electron-hole radiative recombination rate.
Growth Mechanism of Microcrystalline Silicon Deposited by ECRCVD
Authors: Beckers I. , Conrad E. , Müller P. , Nickel N. H. , Sieber I. , Fuhs W. 
Published: April 2011

AbstractMicrocrystalline silicon (μc-Si) films were prepared by electron cyclotron resonance assisted chemical vapor deposition (ECRCVD) using helium, argon and hydrogen dilution. The crystalline fraction was estimated from Raman backscattering spectra and scanning electron-microscopy (SEM) was used to obtain information on roughness and homogeneity of the films. For hydrogen dilution the highest crystallinity (Xc = 85 %) occurs at a ratio of ΔH = [H2]/([H2]+[SiH4])= 0.98. At the same time the deposition rate decreases continuously with increasing H2 dilution. These results are consistent with the idea that H etching promotes the growth of μc-Si. At ΔH > 0.98 a Xc decreases due to a H mediated transition of small crystallites into amorphous tissue. The implications of these results for the growth mechanisms are discussed.
Photocarrier Recombination in Microcrystalline Silicon Studied by Light Induced Electron Spin Resonance Transients
Authors: Müller J. , Finger F. , Malten C. , Wagner H. 
Published: April 2011

AbstractTo get information on the density of states distribution and the photocarrier recombination in microcrystalline silicon (μc-Si:H), samples with various amounts of n- and p-type doping are studied with electron spin resonance (ESR) and stationary and time-resolved light induced ESR. The intensity of the dark ESR signals from dangling bonds (DB) and conduction electrons (CESR) is investigated as a function of the doping level. The DB signal has a flat distribution over a wide doping range while the CESR signal strongly increases with n-type doping. Upon illumination with white or infrared light both resonances are enhanced with an intensity that depends on the doping level. The decay of the light induced signal and the dependence in time and intensity of the residual signal on different initial excitation energies and dark/light -sequences is studied. The results are discussed with a schematic band diagram for μc-Si:H. The existence of a potential barrier is proposed which spatially separates photogenerated carriers. A large band-offset between crystalline and disordered regions is further suggested.
Injection Electroluminescence from Thin Film p-i-n Structures made from Nanocrystalline Hydrogenated Silicon
Authors: Andreev A. A. , Averbouch B. Y. , Mavlyanov P. , Aldabergenova S. B. , Albrecht M. , Stenkamp D. , Strunk H. P. 
Published: April 2011

AbstractNanocrystalline silicon films are prepared by plasma enhanced chemical vapour deposition of silane under the conditions of high hydrogen dilution (3:100). The film structure consists of nanoclusters 0.8 to 5 nm in size (volume fraction 30%) embedded in an amorphous matrix. The Taue gap of the amorphous matrix is 1.95 to 2.05 eV depending on deposition parameter. These films are characterized as regards photoluminescence (PL) and, prepared to p-i-n structures, electroluminescence (EL). The PL and EL agree in (i) luminescence peak at 1.9 eV, i.e. small Stokes shift, (ii) almost no temperature dependence between 77 K and 293 K, (iii) fast kinetics with time constant of a few 10−8 s. These data can be understood in terms of quantum confinement in Si nanocrystallites smaller than around 2 nm. The EL in addition exhibits a luminescence band extending up to 3 eV, which can be interpreted by interband transition due the hot carriers.
Synthesis of Polyvanadates from Solutions
Authors: Livage J. , Bouhedja L. , Bonhomme C. , Henry M. 
Published: April 2011

ABSTRACTA wide range of polyvanadates can be synthesized from aqueous solutions. Vanadium oxide gels V2O5nH2O are formed around the point of zero charge (pH≈2). They exhibit a ribbon-like structure. Weak interactions between these ribbons lead to the formation of mesophases in which vanadium oxide gels or sols behave as nematic liquid crystals. Organic species can be easily intercalated between these oxide ribbons leading to the formation of hybrid nanocomposites made of alternative layers of organic and inorganic components. Hybrid nanophases can also be formed above the point of zero charge, in the presence of large organic ions such as [N(CH3)4]+. They often exhibit layered structures in which organic cations lie between the polyvanadate planes. Cluster shell polyvanadates have been obtained in the presence of anions such as Cl− or I−. They are made of negatively charged polyvanadate hollow spheres in which the anion is encapsulated. Organic cations then behave as counter ions for the formation of the crystal network.
Magnetic Microstructure of a Nanocrystalline Ferromagnet - Micromagnetic Model and Small-Angle Neutron Scattering
Authors: Weissmüller J. , McMichael R. D. , Barker J. , Brown H. J. , Erb U. , Shull R. D. 
Published: April 2011

ABSTRACTWe report on a combined theoretical and experimental study of the magnetic microstructure of a single component, single phase, Pore-free nanocrystalline ferromagnetic material. From the equations of micro-magnetics we conclude that the magnetic microstructure is the convolution product of an anisotropy field microstructure and of a response function with a correlation length lH that depends on the applied field Ha. We derive equations for small angle neutron scattering by such structures, and present experimental scattering data for electrodeposited nanocrystalline Ni, the first where for a wide range of Ha the dominant scattering contribution is from the purely magnetic microstructure, not from nuclear or magnetic contrast at pores or second phases. The variation of the scattering cross section with Ha is in excellent agreement with the theory, indicating that the underlying changes in the magnetic microstructure with Ha are not displacements of domain walls, but changes in lH and hence in the magnetic response to an entirely stationary anisotropy field microstructure. At 20K the anisotropy fields are dominated by magnetocrystalline anisotropy, but at 300K the perturbation is from a much stronger interaction which maintains some moments aligned antiparallel to the field direction at Ha as high as 1.4MA/m (18kOe).
Enhanced Thermal Conductivity through the Development of Nanofluids
Authors: Eastman J. A. , Choi U. S. , Li S. , Thompson L. J. , Lee S. 
Published: April 2011

ABSTRACTLow thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids required in many industrial applications. To overcome this limitation, a new class of heat transfer fluids is being developed by suspending nanocry stalline particles in liquids such as water or oil. The resulting “nanofluids” possess extremely high thermal conductivities compared to the liquids without dispersed nanocrystalline particles. For example, 5 volume % of nanocrystalline copper oxide particles suspended in water results in an improvement in thermal conductivity of almost 60% compared to water without nanoparticles. Excellent suspension properties are also observed, with no significant settling of nanocrystalline oxide particles occurring in stationary fluids over time periods longer than several days. Direct evaporation of Cu nano-particles into pump oil results in similar improvements in thermal conductivity compared to oxide-in-water systems, but importantly, requires far smaller concentrations of dispersed nanocrystalline powder.
Polymerizable Complex Synthesis of Nanocomposite BaTi4/O9 Photo-Catalytic Materials
Authors: Kakihana Masato 
Published: April 2011

ABSTRACTThe “polymerizable complex (PC)” technique, a kind of gel technologies, is based on formation of a polyester resin precursor in which various metal ions can be uniformly distributed keeping their initial stoichiometric ratio. The approach allows for the synthesis of multicomponent oxides at reduced temperatures. Feasibility of the PC method is demonstrated for the synthesis of BaTi4O9 at 700–900 °C. BaTi4O9 was subsequently converted to nanocomposite materials by modifying its surface with ultrafine particles of RuO2, and they were used as photocatalysts for decomposition of water into H2 and O2 under irradiation of light from a high-pressure Hg lamp operated at 100 W. High-resolution transmission electron microscopic observations indicates uniform dispersion of spherical RuO2 particles of ∼2 nm in diameter on the host BaTi4O9 surface. The nanocomposite BaTiO9/RuO2 (1 wt % Ru relative to BaTi4O9) material prepared by the PC method at 800 “C showed a photo-catalytic activity ∼3 times higher than that of a material prepared by the conventional ceramic technique at 1100 °C.
Preparation and Sintering of Silica-Doped Zirconia by Colloidal Processing
Authors: Uchikoshi T. , Sakka Y. , Ozawa K. , Hiraga K. 
Published: April 2011

ABSTRACTSilica-doped (SiO2= 0–1.0 mass%) zirconia (3 mol% Y2O3-doped tetragonal ZrO2) compacts are prepared from hetero-coagulated and well-dispersed suspensions by colloidal processing. The suspensions are consolidated by a pressure filtration technique. The green density of the compacts consolidated from the well-dispersed suspensions is higher than that from the hetero-coagulated suspensions. The lower density of the latter compacts is improved by a subsequent cold isostatic pressing (CIP) at 400 MPa. The sinterability of the compacts at 1200 °C is greatly affected by the amount of doped silica. The densification and grain growth are hindered by silica doping above 0.3 wt% at 1200 °C. All the compacts are densificated to a relative density of above 99% by sintering at 1300 °C for 2 h.
Ferroelectric Lead Zirconate Titanate Nanocomposites for Thick-Film Applications
Authors: Yao Kui , Zhu Weiguang , Yao Xi 
Published: April 2011

ABSTRACTIn this paper, we report our experimental results of lead zirconate titanate (PZT) thick-films prepared from the sol-gel derived nanocomposites. Transparent Pb-Zr-Ti-B-Si gels were synthesized from various metal organic precursors. PZT grains with the size of one hundred nanometers were homogeneously grown from the gels in the annealing process. Then PZT thick-films were prepared using the gel-derived glass-ceramic powders with average particle size below 300 nm. Surficial morphology, dielectric and ferroelectric properties of the films were studied. The characteristics of such films are attributed to the nano-sized composite structure of the gel-derived PZT glass-ceramic precursors.