bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Increased Response Time in Hydrogenated Microcrystalline Silicon - A Fermi Level Effect or a Structural Effect in a Grainy Material?
Authors: Grebner S. , Popovic P. , Furlan J. , Gu Q. , Schwarz R. 
Published: April 2011

AbstractThe typical photocurrent decay time τR in intrinsic prepared hydrogenated microcrystalline silicon (μc-Si:H) is around lms similar to its n-doped amorphous counterpart (a-Si:H:P). Depending on the crystalline fraction Xc, the μc-Si:H films show an activation energy near to or below 0.5eV. To find out if this analogy ofτR could be due to a Fermi level shift or to the grainy structure in gc-Si:H films, we have studied the behaviour of τR in doped a-Si:H and gc-Si:H films of different XC. One-dimensional numerical simulation based on the Multiple Trapping Model (MTM) can explain this increase in terms of a Fermi level shift towards the conduction band. On the other hand, detailed measurements for temperatures from 100 to 400 K point to carrier trapping in deep states, most probably located at grain boundaries.
Correlation Between Electrical-Optical and Structural Properties of Microcrystalline Silicon N Type Films
Authors: Martins R. , Macarico A. , Ferreira I. , Nunes R. , Bicho A. , Fortunato E. 
Published: April 2011

AbstractWide band gap microcrystalline silicon films have aroused considerable interest since they combine some electro-optical advantages of amorphous and crystalline materials highly important to produce electro-optical devices such as TFTs and solar cells. In this paper we present results concerning the electro-optical characteristics of highly transparent and conductive n-type µc-Si based films. Here, emphasis is given to the production of n-type ýtc-films with optical gaps of 2.3 eV and dark conductivity's of 6.5 Scm-1
Drift Mobility Measurements in Porous Silicon
Authors: Tsybeskov L. , Peng C. , Fauchet P. M. , Gu Q. , Schiff E. A. 
Published: April 2011

AbstractModulated electroluminescence (EL) measurements performed on a series of porous silicon (PSi) diodes are presented. The maximum response time of the devices scales with the square of the PSi layer thickness and inversely with the applied forward bias voltage. These scaling results indicate that the maximum response time is a carrier transit time from which a drift mobility μ of 10−4 cm2/Vs is deduced at room temperature. Time-of-flight transport measurements on PSi are in qualitative agreement with this value for μ in addition, they identify μ as the electron mobility and show that transport is dispersive, in contrast to the interpretation of the modulated EL experiments.
Characterization of the Visible Photoluminescence from Porous a-Si:H and Porous a-Si:C:H Thin Films
Authors: Estes M. J. , Hirsch L. R. , Wichart S. , Moddel G. 
Published: April 2011

AbstractWe report on the influence of doping, temperature, porosity, and bandgap on the visible photoluminescence properties of anodically-etched porous a-Si:H and a-Si:C:H thin films. Only boron-doped, p-type a-Si:H or a-Si:C:H samples exhibited any visible photoluminescence. We see evidence of discrete defect or impurity levels in temperature-dependent luminescence measurements. Unlike in porous crystalline silicon, we see no correlation of luminescence energy with porosity. We do, though, observe a correlation of luminescence energy with bandgap of the starting a-Si:C:H films. We discuss the implications of these observations on the nature of the luminescence mechanism.
The Stability Improvement of a-Si:H Films for Photovoltaic Applications
Authors: Budaguan B. G. , Aivazov A. A. , Meytin M. N. 
Published: April 2011

AbstractThe origin of metastability in a-SiH films deposited at different deposition conditions has been investigated by joint analysis of light-induced defect generation kinetics (Staebler-Wronski Effect) and differential scanning calorimetry (DSC) measurements. Light-induced defect generation kinetics were measured at elevated temperatures of 80-150°C_ DSC measurements were performed in a temperature range of 20°C - 570°C. The films microstructure were studied by IR spectroscopy analysis.The simulation of DSC curves has been used to deduce the kinetics of the low-temperature exothermic peak (LTEP) observed at 80-150° C. It was found that kinetic parameters of LTEP and SW effects has the same dependence on microstructure parameters, γ, which suggests their common nature. The analysis of a-SiH stability improvement concerning the influence of films microstructure on the kinetics of relaxation processes is presented.
Finite Element Calculations to Optimize the Design of a Stressor for Strained Induced Quantum Wires and Quantum Dots in GaAs
Authors: Pinardi K. , Jain S. C. , Maes H. E. 
Published: April 2011

AbstractWe have calculated the normalized stress σfxx/σ0 (σ0 is the stress in the large area stressor) in the stressor and σsxx/σ0 in the substrate for values of RE = Ef/Es (Ef is the Young's modulus of the stressor and Es, is the Young's modulus of the substrate) in the range 0.5 to 1.2. Substrate stresses for 13 stripe stressor samples are also calculated for RE = 0.9 which corresponds to an InGaAs stressor on GaAs with an In concentration of about 25%. It is found that for any given 1, the stress at a given depth increases monotonically as h increases (1 and h are the halfwidth and thickness of the stressor). The increase is rapid in the beginning for small value of h (l/h > 2). It becomes slow for 1/h < 2 and saturates at l/h = 0.5. For large i/h(l/h > 50) there are two stress wells in the substrate separated by a barrier. For l/h = 20 the two wells merge into one well with a flat bottom. As l/h decreases further the bottom curves downward, and for l/h < 2 the shape of the stress distribution curve resembles that of a parabola. The stress σsxx/σ0 decays rapidly with distance z from the interface. It is reduced to 1/3 of its value near the interface at z ˜ h. It is therefore necessary to construct the active layer close to the interface. Quality of the interface plays a dominant role in the Quantum structures fabricated in this manner. The shape and the strength of the stress well cannot be changed independently in these structures. We have suggested novel stressor designs to remove this limitation.
Electron Cyclotron Resonance Etching of SiC in SF6/O2 and NF3 /O2 Plasmas
Authors: Ren F. , Grow J. M. , Bhaskaran M. , Lee J. W. , Vartuli C. B. , Lothian J. R. , Flemish J. R. 
Published: April 2011

AbstractEtching of β-SiC with electron cyclotron resonance (ECR) system was investigated. Anisotropic and smooth etching of SiC was demonstrated with SF6/O2 based discharges. The root-mean-square roughness increases from 35 nm to 56 nm for as deposit and etched sample, respectively. The addition of small amount oxygen enhanced the etch rate of SiC slightly, but further increase of oxygen content reduced the etch rate which resulted from dilution of F ion and free radical densities. NF3/O2 based discharges also showed same trends and produced anisotropicly etching. However, the smoothness is not as good as SF6/O2 based discharges.
A Study of Low-Temperature Grown Gap by Gas-Source Molecular Beam Epitaxy
Authors: Bi W. G. , Mei X. B. , Kavanagh K. L. , Tu C. W. , Stach E. A. , Hull R. 
Published: April 2011

AbstractWe report the effects of growth conditions on the strain and crystalline quality of lowtemperature (LT) grown GaP films by gas-source molecular beam epitaxy. At temperatures below 160 °C, poly-crystalline GaP films are always obtained, regardless of the PH3 low rate used, while at temperatures above 160 °C, the material quality is affected by the PH3 flow rate. Contrary to compressively strained LT GaAs, high-resolution X-ray rocking curve measurement indicates a tensile strain of the LT GaP films, which is considered to be due to PGa antisite defects. The strain is found to be affected by the PH3 flow rate, the growth temperature, and post-growth annealing. Contrary to LT GaAs, no P precipitates are observed in cross-sectional transmission electron microscopy.
Dry Etching of InGaP and AlInP in CH4/H2/Ar
Authors: Lee J. W. , Pearton S. J. , Santana C. J. , Lambers E. S. , Abernathy C. R. , Hobson W. S. , Ren F. 
Published: April 2011

AbstractElectron Cyclotron Resonance (ECR) plasma etching with additional if-biasing produces etch rates ≥ 2,500Å/min for InGaP and AlInP in CH4/H2/Ar. These rates are an order of magnitude or much higher than for reactive ion etching conditions (RIE) carried out in the same reactor. N2 addition to CH4/H2/Ar can enhance the InGaP etch rates at low flow rates, while at higher concentrations it provides an etch-stop reaction. The InGaP and AtlnP etched under ECR conditions have somewhat rougher morphologies and different stoichiometries up to ˜200Å from the surface relative to the RIE samples.
Temperature Dependence of the Electrical Transport of Carbon Doped Gan
Authors: Geerts Wim , MacKenzie J.D. , Abernathy C.R. , Pearton S.J , Schmiedel Thomas 
Published: April 2011

AbstractThe temperature dependence of the Hall voltage and resistivity of highly carbon doped GaN were measured. From the sign of the Hall voltage, the material appears to be p-type. Charge transport takes place in an impurity band and the valence band. The effective activation energy as estimated from the maximum in the temperature versus Hall voltage relation is 10–30 meV.
Parametric Study of Compound Semiconductor Etching Utilizing Inductively Coupled Plasma Source
Authors: Constantine C. , Johnson D. , Barratt C. , Shul R. J. , Mcclellan G. B. , Briggs R. D. , Rieger D. J. , Karlicek R. F. , Lee J. W. , Pearton S. J. 
Published: April 2011

AbstractInductively Coupled Plasma (ICP) sources are extremely promising for large-area, highion density etching or deposition processes. In this review we compare results for GaAs and GaN etching with both ICP and Electron Cyclotron Resonance (ECR) sources on the same singlewafer platform. The ICP is shown to be capable of very high rates with excellent anisotropy for fabrication of GaAs vias or deep mesas in GaAs or GaN waveguide structures.
Low Interface State Density Oxide-GaAs Structures Fabricated by In-Situ Molecular Beam Epitaxy
Authors: Passlack M. , Hong M. 
Published: April 2011

AbstractWe have extended the spectrum of molecular-beam epitaxy (MBE) related techniques by introducing in-situ deposition of oxides. The oxide films have been deposited on clean, atomically ordered (100) GaAs wafer surfaces using molecular beams of gallium-, magnesium-, silicon-, or aluminum oxide. Among the fabricated oxide-GaAs heterostructures, Ga2O3-GaAs interfaces exhibit unique electronic properties including an interface state density Dit in the low 1010 cm−2eV−1 range and an interface recombination velocity S of 4000 cm/s. The formation of inversion layers in both n- and p-type GaAs has been clearly established. Further, thermodynamic and photochemical stability of excellent electronic interface properties of Ga2O3-GaAs structures has been demonstrated.
Self Organized Growth in Thulium Doped Gaas Using MBE
Authors: Bennett M. R. , Singer K. E. , Wright A. C. , Jafri Z. H. 
Published: April 2011

AbstractThe growth of epitaxial GaAs doped with the rare earth thulium (Tm) by MBE is reported for the first time. The nature of the incorporation of Tm has been studied using SIMS, RBS, TEM, PL and DCXRD. Sharp doping profiles have been observed by SIMS from samples doped in a staircase structure. Under standard GaAs growth conditions, TEM has revealed a solubility limit of ∼5×1019cm−3, above which Tm precipitates as spherical nano-particles of uniform size (1.3–1.7nm). High resolution TEM has provided no evidence for strain relaxation around these precipitates. Growth at higher substrate temperatures (≥620°C) or at As:Ga ratios close to stoichiometry, results in the formation of precipitate wires and/or bifurcated structures (“quantum trees”) aligned approximately in the direction of growth. Such behaviour is in common with that of Er in GaAs and suggests that the precipitates result from the self-organised growth of TmAs. Mechanisms for the formation of the quantum wires and trees are suggested. Initial photoluminescence spectra from these samples show two groups of narrow Tm3+ intra 4f transition lines corresponding to the 3H5 – 3H6 (∼1.01eV/1.2μm) and 3H4 – 3H6 (∼ 0.71eV/1.7μm) transitions. The spectra exhibit an excellent correlation with those obtained from samples grown by MOVPE and also those implanted with Tm by other groups.
Characterization of 4H-SiC JFETs for Use in Analog Amplifiers Capable of 723K Operation
Authors: Casady J. B. , Sheridan D. C. , Dillard W. C. , Johnson R. W. 
Published: April 2011

AbstractDiscrete, buried-gate 4H-SiC JFETs (W/L = 1 mm/5 μm) were packaged and characterized at temperatures ranging from 290 K to 773 K for use in a hybrid, 4H-SiC analog amplifier. A contaminated passivation oxide was found to limit high-temperature operation initially, but upon removal of the passivation layer the devices demonstrated stable operation to 773 K with adequate amplification (Av greater than 200 V/V) up to 673 K. From the 16 devices tested, a peak extrinsic saturated transconductance (gmsa) of 27.1 mS/mm was measured at 308 K, corresponding to a channel mobility of 400 cm2/V.s, excluding significant series resistance effects.
Chemical and Structural Characterization of the Ni-Ti Alloy/6H-SiC Contacts
Authors: Levit M. , Grimberg I. , Weiss B.-Z. , Eizenberg M. 
Published: April 2011

AbstractNi-Ti alloy is a promising candidate for high-temperature contact metallization for SiC electronic devices. In the present study Ni-Ti alloy thin films (100 nm) of two different compositions (Ni90Ti10 and Ni50Ti50) were coevaporated on 6H-SiC substrate. Interfacial reactions, microstructure, compositional changes, and phase formation were investigated as functions of heat-treatments in the range of 400–800 °C. The study was carried out using Auger electron spectroscopy, x-ray diffraction, and analytical transmission electron microscopy. In the case of the Ni90Ti10 alloy the interaction was found to begin at 450 °C. Ni and C are the dominant diffusing species. The reaction zone is divided into three layers. In the first layer, adjacent to the SiC substrate, the presence of a Ni-rich silicide, Ni2Si, and C precipitates, was observed. The second layer is composed mainly of TiC, while the third - of Ni2 Si. In the case of the Ni50 Ti50 alloy the interaction began at 800 °C. Carbon is the dominant diffusant. The reaction zone is divided into two layers. The first, next to the substrate layer is composed of epitaxially grown TiC and the second - of Ni3Ti2Si compound. A thin (∼5 nm) amorphous discontinuous layer was found at the TiC/SiC interface. Factors controlling phase formation in the Ni-Ti/SiC system are discussed.
Dry Etch Damage In InN, InGaN and InAIN
Authors: Pearton S. J. , Lee J. W. , MacKenzie J. D. , Vartuli C. B. , Donovan S. M. , Abernathy C. R , Shul R. J. , Ren F. , Lothian J. R. 
Published: April 2011

AbstractDamage introduction in III-V nitrides during dry etching can be simulated by exposingthe samples to pure Ar plasmas for study of the physical (ion-bombardment) effects.Changes in conductivity of InN, In0.5Ga0.5N and In0.5Al0.5N layers exposed to Ar plasmasunder both Electron Cyclotron Resonance and reactive ion etching conditions have beenmeasured as a function of rfpower, pressure and exposure time. The combination of highmicrowave and high rf powers produces large increases (10-_104times) in sheet resistanceof the nitrides, but conditions more typical of real etching processes (rf power < 150W) donot change the bulk electrical properties. The nitrides are more resistant to damageintroduction than other III-V semiconductors. The removal of damage-related trapsoccurs with an activation energy of ∼2.7eV. High ion currents during ECR etching canproduce substantial conductivity changes, whereas the lower currents under RIEconditions do not affect the nitrides. It is difficult to avoid preferential loss of N in thenear-surface of these materials, which leads to leakage currents in rectifying metal contactsdeposited on these surfaces.
Thermodynamic Analysis and Growth Characterization of thick GaN films grown by Chloride VPE using GaCl3/N2 and NH3/N2
Authors: Lee Heon , Yuri Masaaki , Ueda Tetsuzo , Harris James S. 
Published: April 2011

AbstractThermodynamic calculations were carried out on chloride transport vapor phase epitaxy of GaN using GaCl3/N2 and NH3/N2. At typical growth temperature and gas flow rates, both GaN formation and gas phase etching reactions of GaN are thermodynamically favored. Under thermodynamic equilibrium, most ammonia should decompose to nitrogen and hydrogen gases and gas phase etching of GaN occurs by HCI. From experimental measurements, less than 10% of the incoming ammonia decomposes and under this condition, GaN formation from GaCl3 /N2, and NH3 /N2 is thermodynamically favored. Higher V/III ratios give a larger driving force for GaN fromation. These calculations match our experimental results. Experimentally, we have optimized the growth conditions of GaN. High crystalline quality thick GaN films (10 ˜15μm) were grown on c-Al2O3. The GaN films show band edge emission dominated PL at both room temperature and 77 K. Only one set of diffraction peaks from (1012) planes with 60° spacing in the φ-scan of X-ray diffraction are observed. This indicates that the GaN films grown on c-Al2O3 are single crystalline. Typical growth rates were about 10 ˜ I5μm/hr and typical Hall mobility values of GaN films were in the range of 3 to 40 cm2/Vsec.
Stability and Reconstruction of, β-SiC (100) Surfaces
Authors: Gutierrez R. , Frauenheim Th. 
Published: April 2011

AbstractWe present a detailed investigation of β-SiC (100) surface reconstructions. Minimal energy configurations at both C- and Si-terminations are determined by using a density-functional based molecular-dynamics method. We provide information on the energetic order of various metastable surfaces and describe the geometrical details. In addition, we also study Si- and C-enriched configurations.
Computer Simulation of Surface Diffusion of Silicon and Carbon Adatoms on SiC(001)
Authors: Bhatti Q. A. , Moran G. J. , Matthai C. C. 
Published: April 2011

AbstractWe have performed molecular dynamics simulations of adatom diffusion on the SiC(001) surface and found that the barriers for carbon adatoms is less than that for silicon adatoms. The diffusion paths were also found to be temperature dependent and at high temperatures the adatom diffusion constant was found to of the order of 10−5 cm2 s−1.
Theoretical Prediction of Zinc Blende Phase GaN Avalanche Photodiode Performance Based on Numerically Calculated Electron and Hole Impact Ionization Rate Ratio
Authors: Kolnik J. , Oguzman I. H. , Brennan K. F. , Wang R. , Ruden P. P. 
Published: April 2011

AbstractIn this paper, we present the first calculations of the electron and hole initiated interband impact ionization rate in zinc blende phase GaN as a function of the applied electric field strength. The calculations are performed using an ensemble Monte Carlo simulator including the full details of the conduction and valence bands along with a numerically determined, wave-vector dependent interband ionization transition rate determined from an empirical pseudopotential calculation. The first four conduction bands and first three valence bands, which fully comprise the energy range of interest for device simulation, are included in the analysis. It is found that the electron and hole ionization rates are comparable over the full range of applied electric field strengths examined. Based on these calculations an avalanche photodiode, APD, made from bulk zinc blende GaN then would exhibit poor noise and bandwidth performance. It should be noted however, that the accuracy of the band structure employed and the scattering rates is presently unknown since little experimental information is available for comparison. Therefore, due to these uncertainties, it is difficult to unequivocally conclude that the ionization rates are comparable.
Tem Analysis of the Observed Phases During the Growth of Oriented Diamond on Nickel Substrates
Authors: Liu W. , Yang P. C. , Tucker D. A. , Wolden C. A. , Davis R. F. , Glass J. T. , Prater J. T. , Sitar Z. 
Published: April 2011

AbstractTransmission electron microscopy (TEM) was used to investigate the interfacial microstructures and phases involved in the nucleation and growth of the oriented diamond on Ni substrates by a multi-step growth process. A molten surface layer is formed during the process, which appears to be critical for both promotion of the diamond nucleation and suppression of graphite formation. Cross-section TEM analysis revealed that a polycrystalline nickel carbide interfacial structure exists between the diamond particles and the single crystal Ni substrate. X-ray diffraction analysis (XRD) identified the carbide phase as Ni4C. It is suggested that the Ni4C is formed in the molten layer and stabilizes sp3C precursor for diamond nucleation.
Structural Defects and Their Relationship to Nucleation of Gan Thin Films
Authors: Gian Weida , Skowronski Marek , Rohrer Greg S. 
Published: April 2011

AbstractMicrostructure and extended defects in α-GaN films grown by organometallic vapor phase epitaxy on sapphire substrates using low temperature AIN (or GaN) buffer layers have been studied using transmission electron microscopy. The types and distribution of extended defects were correlated with the film growth mode and the layer nucleation mechanism which was characterized by scanning force microscopy. The nature of the extended defects was directly related to the initial three-dimensional growth. It was found that inhomogeneous nucleation leads to a grain-like structure in the buffer; the GaN films then have a columnar structure with a high density of straight edge dislocations at grain boundaries which are less likely to be suppressed by common annihilation mechanisms. Layer-by-layer growth proceeds in many individual islands which is evidenced by the observation of hexagonal growth hillocks. Each growth hillock has an open-core screw dislocation at its center which emits monolayer-height spiral steps.
Electron Scattering by Native Defects in Ill-V Nitrides and their Alloys
Authors: Hsu L. , Walukiewicz W. 
Published: April 2011

AbstractWe have calculated the electron mobilities in GaN and InN taking into consideration scattering by short range potentials, in addition to all standard scattering mechanisms. These potentials are produced by the native defects which are responsible for the high electron concentrations in nominally undoped nitrides. Comparison of the calculated mobilities with experimental data shows that scattering by short range potentials is the dominant mechanism limiting the electron mobilities in unintentionally doped nitrides with large electron concentrations. In the case of AlxGal1−xN alloys, the reduction in the electron concentration due to the upward shift of the conduction band relative to the native defect level can account for the experimentally measured mobilities. Resonant scattering is shown to be important when the defect and Fermi levels are close in energy.
The Relationship Between Micropipes and Screw Dislocations in Pvt Grown 6H-Sic
Authors: Giocondi Jennifer , Rohrer Gregory S. , Skowronski Marek , Balakrishna V. , Augustine G. , Hobgood H. M. , Hopkins R. H. 
Published: April 2011

AbstractThe growth surface of a 6H-SiC boule, grown by physical vapor transport, was examined using scanning force microscopy. The dimensions of surface/micropipe intersections and screw dislocation Burgers vectors have been determined from topographic data. All micropipes are positioned along the lines of super screw dislocations with a Burgers vectors of at least 4 times the c-axis repeat distance (15.2 Å). Perfect c-axis screw dislocations with Burgers vectors of only 15.2 Å are stable and do not have open cores. Measurements show that micropipe core radii, determined indirectly from the width of the craters formed at the surface/micropipe intersections, increase with the square of the dislocation Burgers vector.