bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis, Structural and Optical Characterization of Zinc Chalcogentdes in Novel Solid State Hosts
Authors: Moran Kelly L. , Ott Andrew W. , Gier Thurman E. , Harrison William T. A. , Eckert Hellmut , Stucky Galen D. 
Published: March 2011

ABSTRACTSeveral series of sodali te analogues of unit cell composition M8X2(TO2)12, where M is Zn or Cd, X is a chalcogen, and T is a tetrahedral cation B, or Be in combination with Si or Ge, have been prepared. An M4X tetrahedron, which is the first coordination sphere of the bulk semiconductor MX, sits at the center of each sodalite cage. These materials have been structurally characterized by solid state 77Se and 125STe MAS NMR and by powder X-ray diffraction. Diffuse reflectance optical absorption spectra are reported for each series. The borates have optical properties similar to the bulk MX whereas the beryllosilicates and germanates exhibit large blue shifts in the absorption spectra.
Optical Transitions on CdS/CdTe CVD Heterostructures
Authors: Boemare Claude , Nazare M H 
Published: March 2011

ABSTRACTWide-band gap II-VI semiconductors have direct bandgaps which cover the energy range from the red to the u-v. This makes such compounds ideal for optoelectronic applications. CdS has a band gap of 2.42 eV and becomes potentially useful for the green region of the spectrum. However, because CdS has a preference to adopt the hexagonal wurtzite structure, epitaxial growth of this semiconductor is complicated. Nevertheless succesful growth of CdS layers onto CdTe is possible. We report a detailed photoluminescence study of CdS/CdTe heterostructures grown by CVD. The CdS layers have high quality hexagonal structure. Luminescence lines are narrow enough and we could detect a splitting ocurring on the excited state of a neutral acceptor bound exciton, at 2.5462 eV.
Remote Ecr Plasma Deposition of Diamond Thin Films from Water-Methanol Mixtures
Authors: Singh R. K. , Gilbert D. , Tellshow R. , Koba R. , Ochoa R. , Simmons J. H. , Holloway P. H. , Rodgers J. , Buckle K. 
Published: March 2011

ABSTRACTWe have applied an electron cyclotron resonance technique to deposit diamond thin films on various substrates under remote plasma, low temperature (600°C) and low pressure (60 mTorr) conditions. Diamond films were grown on different substrates (silicon, molybdenum) with varying concentrations of precursor gases (methanol and water). A positive substrate bias (50 to 60 V) was found to be essential for the growth of diamond films onto substrates positioned 16 cm below the ECR plasma. The films were characterized by Raman, X-ray diffraction and scanning electron microscopy for microstructure, phase purity and chemical bonding characteristics. The effect of various processing parameters including gas pressure, gas composition, substrate temperature and bias have also been analyzed.
Self-Compensation and Doping Problems in ZnSe
Authors: Laks David B. , Van de Walle Chris G. 
Published: March 2011

ABSTRACTWe examine native-defect compensation, solubility limits, and dopant self-compensation in ZnSe. Our results are based on a formalism, using first-principles density-functional theory, that treats dopant atoms and native defects on an equal footing. For the case of acceptor doping of ZnSe with Li, we find that compensation due to interstitial Li donors and to native donor defects can be reduced to a tolerable level by carefully adjusting the growth conditions. A more serious impediment to Li doping comes from the solubility limit of Li in ZnSe.
A Comparison of the Wurtzite and Zincblende Band Structures for SiC, AlN and GaN
Authors: Lambrecht W. R. L. , Segall B. 
Published: March 2011

ABSTRACTTotal energy and band structure results of linear-muffin-tin orbital calculations within the atoiuic-spliere-approxiiuation are presented for SiC, GaN and A1N in the zincblende and the wurtzite structure. We discuss the origin of the directness or indirectness and the relative magnitudes of the band gaps.
Deposition of Flame Grown Diamond Films in a Controlled Atmosphere
Authors: Doverspike Kathleen , Butler James E. , Freitas Jaime A. 
Published: March 2011

ABSTRACTPolycrystalline diamond films were synthesized both by using an open atmosphere combustion flame, and also using a combustion flame in an enclosed chamber. By operating the pre-mixed oxy-acetylene torch in a chamber, we were able to vary the atmosphere around the flame in a controlled manner and study the effects on the diamond films. Varying the atmosphere around the flame is of interest to control the incorporation of unwanted gases, such as room air, and to obtain finer control over the flame properties. We report on the properties of films grown in the open atmosphere and in the chamber with oxygen and argon.
The Einstein Relation in Superlattices OP Wide-Band Gap Semiconductors Onder Cross-Field Configuration
Authors: Ghatak Kamakhya P. , De Badal 
Published: March 2011

ABSTRACTin this paper we study the Einstein relation in superlattices of wide-band gap semiconductors under crossfield configuration and the for.-ning materials incorporating spin and broadening of Landau levels, it is found, taking GaAs/AÀAs superlattice as an example that the diffusivity-mobility ratio increases with increasing electron concentration and oscillates with inverse quantizing magnetic field due to SdH effect. Thetheoretical analysis is in agreement with the suggested experimental method of determining the same ratio in degenerate materials having arbitrary dispersion laws.
Conductivity Control of AlGaN. Fabrication of AlGaN/GaN Multi-Heterośtructure and their Application to UV/Blue Light Emitting Devices
Authors: Akasaki I. , Amano H. 
Published: March 2011

ABSTRACTThe method for controlling the electrical properties of n-type GaN and AIGaN have been established. Both GaN and AIGaN films having p - type conduction have been realized for the first time. High quality AIGaN/GaN mu I t i-he t er ostrueture showing clear quantum size effect has been fabricated. P-n junction type UV/blue LED with double he t e ros t rue ture have been developed for the first time.
Systematic Studies on Magnetron-Sputtered Indium Nitride
Authors: Bryden W. A. , Ecelberger S. A. , Morgan J. S. , Poehler T. O. , Kistenmacher T. J. 
Published: March 2011

ABSTRACTExtensive and systematic studies on reactive magnetron sputtering of InN thin films are summarized. The films have been deposited onto several types of substrates, with variations in such process parameters as deposition temperature, partial pressures of reactive and inert gases, sputtering power and gas flows. These films have been characterized by measuring their electrical, optical, structural and morphological properties. It has been shown that epitaxial growth of InN occurs on the basal plane of single-crystal (00.1) sapphire and (001) mica substrates and on the (111) face of cubic substrates such as silicon and zirconia.Two principal problems currently limit the usefulness of thin films of InN. First, although epitaxy can be attained with the proper choice of substrate type and deposition temperature, the resulting film is an agglomerate of epitaxial grains -- not a single crystal. Second, all magnetron sputtered InN films prepared to date have low mobility and high carrier concentration (likely due to nitrogen vacancies). In an attempt to address these problems, experiments on the growth and characterization of sputtered InN films have been carried out and are discussed here with particular emphasis on seeded heteroepitaxial growth and the effects of film deposition temperature.For example, it was found early that the growth of InN on the bare surface of several crystalline substrates at growth temperatures near 350°C results in a morphological transition that causes a degradation of semiconducting properties. The predeposition of an AIN seed layer inhibits this morphological transition and stabilizes a relatively high mobility state, but a still too high carrier concentration obtains. Further progress critically depends on optimizing the seeded heteroepitaxial growth technique in conjunction with the achievement of InN films with lower density of nitrogen vacancies.
A Comparative Study of GaN Epitaxy on Si(001) and SI(111) Substrates
Authors: Lei T. , Moustakas T. D. 
Published: March 2011

ABSTRACTEpitaxial GaN films were grown on Si(001) and (111) substrates, using a two-step process. The films on Si(001) are single crystalline having the zincblende strucutrue, while those on Si(111) have the wurtzite structure. The crystalline qualities of the films were studied by X-ray diffraction. While the zincblende GaN has a perfect cubic structure, the wurtzitic GaN on Si(111) has a considerable amount of stacking faults along (0002) direction, which gives rise to significant zincblende component with (111) orientation. Room temperature resistivity for both type of GaN films was found to be larger than 100 Ω· cm. The temperature dependence of th resistivity gives a defect level at HOmeV for wurtzitic GaN and 80meV for cubic GaN. Optical studies show that GaN on Si(001) has a gap 3.2eV, and GaN on Si(111) has a gap of 3.4eV at room temperature.
Growth Dependence of Thickness, Morphology and Electrical Transport of InN Over Layers on Ain-Nucleated (00.1) Sapphire
Authors: Kistenmacher T. J. , Ecelberger S. A. , Bryden W. A. 
Published: March 2011

ABSTRACTThe seeded-heteroepitaxial growth, morphology and electrical transport properties of InN overlayers deposited by reactive magnetron sputtering on AIN-nucleated (00.1) sapphire have been investigated. For comparison, InN films were grown directly onto (00.1) sapphire under identical experimental conditions. These unseeded films showed a unimodal growth and were a mixture of textured and broadly heteroepitaxial grains. Low Hall mobility and carrier concentration and high resistivity were typical. In contrast, the AIN-nucleated InN overlayers exhibited a bimodal growth, strongly heteroepitaxial grains, and high Hall mobility. A particularly interesting aspect of the films grown on seeded (00.1) sapphire is the preservation of electrical continuity and high Hall mobility even in the limit of InN overlayers with thicknesses only on the order of 20–40Å.
Epitaxial Growth of AlN on 3C-SiC and Al2O3 Substrates
Authors: Sywe B. S. , Yu Z. J. , Edgar J. H. 
Published: March 2011

ABSTRACTA1N films were grown on the (100) plane of 3C-SiC/Si and the (0001) plane of A12O3 substrates by metalorganic chemical vapor deposition (MOCVD) using trimethylaluminum (TMA) and ammonia (NH3) as the precursors. The deposited films were characterized by X-ray diffraction (XRD) and a Read thin film camera. At 1150°C, preferentially oriented polycrystalline AlN films were obtained on both substrates and the crystal structure was wurtzite. The epitaxial relations were (1010)AlN//(100)SiC//(100)Si and (0001)AlN// (0001)Al2O3. The attempt to grow cubic AlN on 3C-SiC/Si was not successful.
Electrical Properties of Thermally Grown SiO2-SiC Interfaces
Authors: Singh Nitya N. , Rys A. , Ahmed A. U. 
Published: March 2011

ABSTRACTFabrication processes of metal-oxide semiconductor (MOS) capacitors on n-type, Si-face, 6H-SiC were studied. The effects of thermal oxidation conditions at temperatures between 1100 and 1250°C on the electrical properties of MOS capacitors were determined. The wafers were annealed under argon to improve the C-V characteristics. C-V characteristics of AI-SiO2-SiC metal-oxide-semiconductor were measured at high frequency in the dark and under illumination. In the dark inversion does not occur, probably owing to the absence of minority carriers due to the large band gap of 6H-SiC. The accumulation, depletion, and inversion regions were clearly observed when the C-V measurements were made under illumination for both wet and dry thermally grown oxides. The interface trap densities and emission time constants of fast states were determined by ac conductance measurements. From the analysis of data we obtained a total of Fixed charges and the slow interface traps, Nf + NssSlow of 1.5 to 3.3 × 1012 cm-2, fast interface trap densities, NssFast of 0.5 to 1.7 × 1011 cm-2 eV-1 and emission times constant of 0.3 to 1.4 μsec for wet oxidation. For dry oxidation, Nf + N, ssSlow of 3.5 to 11.2 × 10cm-2, NssFast of 0.7 to 1.25 × 1010 cm-2 eV-1 and emission time constants of 0.6 to 2 μsec were obtained.
Submillimeter Optical Properties of Hexagonal Boron Nitride
Authors: Gatesman A. J. , Giles R. H. , Waldman J. 
Published: March 2011

ABSTRACTThe submillimeter optical properties of hot-pressed boron nitride with a hexagonal crystal structure were studied at room temperature from approximately 20 cm-1 to 120 cm-1 (500μm -84 μm) with a Fourier Transform Spectrometer. Several grades were studied and probed both parallel and perpendicular to the material's optic axis. The material was found to behave as a negatively uniaxial birefringent crystal. In one case, the birefringence (Δ = ne - no) was quite large with a value of-0.152. The material's absorption properties were also studied. For certain grades, a modest dichroism was observed. The low absorption (α < 1 cm-1) for grade A at frequencies below 38 cm-1 suggests the possibility for millimeter/submillimeter wave applications. Results are compared with data by other researchers on related materials.
Effects of Reactive Sputtering Parameters on the Growth and Properties of Acoustooptic ZnO Films
Authors: Jacobsohn E. , Shechtman D. 
Published: March 2011

ABSTRACT1 μm ZnO films were deposited on SiO2 by reactive sputtering using a D. C. magnetron gun. The microstructure, orientation and chemistry of the deposited layers were examined. It is shown that the oxygen partial pressure plays an important role in the structure of the layer through a mechanism of surface diffusion.
Effect of Laser Irradiation on Carbon-Implanted Copper Substrates
Authors: Singh Rajiv K. , Viatella John 
Published: March 2011

ABSTRACTWe have analyzed the non-equilibrium thermal effects of pulsed nanosecond lasers on carbon-implanted copper substrates. The thermal effects of pulsed nanosecond lasers were simulated by numerically solving the heat flow equation and taking into account the phase changes which occur at the surface of the irradiated solid. Intense pulsed laser irradiation induces rapid heating at the near surface resulting in melting, followed by rapid quenching of the melt phase. The effect of laser variables (energy density, etc.) on the maximum melt depth, melt-in and solidification velocities and transient temperature profiles have been computed. Maximum melt depths and the surface temperatures were found to increase approximately in a linear manner with pulse energy density. Extremely high average solidification velocities (20–45 m/sec) were calculated which may give rise to solute trapping and other non-equilibrium segregation effects. The change in laser-irradiated characteristics of copper substrates as a result of carbon-ion implantation is also discussed.
Preparation of Pb-Based Ferroelectric thin films by Ion- and Photo-Assisted Deposition
Authors: Hayashi Shigenori , Iijima Kenji , Hirao Takashi 
Published: March 2011

AbstractThin film process for Pb-based perovskite ferroelectrics has been investigated. Synthesis of epitaxial PLZT, PLT and PZT thin films by rfmagnetron sputtering in our laboratory was reviewed. Basic thin film process and applications were discussed. For further investigation, film preparation process was developed by co-deposition and assisted deposition techniques. The substrate temperature required for in-situ preparation of perovskite could be reduced to room temperature by an ion- and photoassisted co-evaporation technique.
Ferroelectric PbZrxTi1-xO3 Thin Films Grown by Organometallic Chemical Vapor Deposition
Authors: Dormans G.J.M. , de Keijser M. , Veldhoven P. J. van 
Published: March 2011

AbstractFor the successful integration of ferroelectric thin films in IC technology, there is a need for a deposition technique capable of growing homogeneous layers at high growth rates over large-area structured substrates. Organometallic chemical vapor deposition (OMCVD) is a promising technique for meeting these demands.Ferroelectric layers of PbZrxTi1-xO3 (PZT) were grown by OMCVD on Pt-coated 10 cm diameter Si-substrates using the precursors tetra-ethyl-lead, tetra-iso-propoxy-titanium and tetra-tertiary-butoxy-zirconium at 700 °C without any post anneal. At this temperature the layers are single phase and highly (h00) and/or (00l) oriented. The layers show good ferroelectric switching properties with high remanent polarizations, but also with high coercive field strengths. Fatigue measurements are presented for these OMCVD grown PZT layers. The layers have a switching lifetime exceeding 1011 cycles at a switching amplitude of 5 V.
Spectroscopic and Microstructural Characterization of Solution Chemistry Effects in Pzt Thin Film Processing
Authors: Schwartz Robert W. , Ink R. A. Ass , Headley T. J. 
Published: March 2011

AbstractFerroelectric PZT 53:47 thin films were prepared by two different solution deposition methodologies. Both routes utilized carboxylate and alkoxide precursors and acetic acid, which served as both a solvent and a chemical modifier. We have studied the effects of solution preparation conditions on film microstructure and ferroelectric properties, and have used NMR spectroscopy to characterize chemical differences between the two precursor solutions. Films prepared by a sequential precursor addition (SPA) process were characterized by slightly lossy hysteresis loops, with a Pr of 18.7 μC/cm2 and an Ec of 55.2 kV/cm. Films prepared by an inverted mixing order (IMO) process were characterized by well saturated hysteresis loops, a Pr of 26.2 μC/cm2 and an Ec of 43.3 kV/cm. While NMR investigations indicated that the chemical environments of both the proton and carbon species were similar for the two processes, differences in the amounts of by-products (esters, and therefore, water) formed were noted. These differences apparently impacted ceramic microstructure. Although both films were characterized by a columnar growth morphology, the SPA derived film displayed a residual pyrochlore layer at the film surface, which did not transform into the stable perovskite phase. The presence of this layer resulted in poor dielectric properties and lossy ferroelectric behavior.
Structural and Electrical Properties of BaTiO3 Thin Film Capacitors
Authors: Shi Z.Q. , Jia Q.X. , Anderson W.A. 
Published: March 2011

AbstractThin film BaTiO3 capacitors were deposited by RF magnetron sputtering. The leakage current was suppressed by more than 3 orders of magnitude if a trace of hydrogen was introduced into the sputtering chamber during film deposition. The introduction of hydrogen gas during sputtering makes the dc conductivity as low as 1×10−13 (Ω−cm)−1 for the amorphous films but still gives the dielectric constant a value of around 17. However, this accomplishment could not be achieved for polycrystal BaTiO3 thin film capacitors. As the substrate temperature increased from room temperature to 700°C, the dielectric constant was increased from 16 to 300 by using Ar + O2 gas. But, the dielectric constant was only around 30 at a deposition temperature of 700°C while the leakage current was decreased when using a gas mixture of Ar + H2 + O2 during sputtering.
Electrochemical Preparation of Barium Titanate Films at Ultra-Low Temperatures
Authors: Venigalla S. , Bendale P. , Ambrose J.R. , Verink E.D. , Adair J.H. 
Published: March 2011

AbstractPreparation of BaTiO3 thin films on titanium substrates by hydrothermal-electrochemical methods at temperatures ranging from 80 to 200°C have recently been reported in literature. In the present work, polycrystalline, homogeneous, and electrically insulating films of BaTiO3 have been electrochemically synthesized at temperatures as low as 55°C. Effects of various electrochemical and thermodynamic parameters such as temperature, solution pH, electrolyte composition, current density, and atmosphere on phase stability and film characteristics have been investigated. Formation of BaTiO3 is favored only under highly alkaline conditions. This finding is consistent with the reported phase stability criteria for BaTiO3 in Ba-Ti-CO2-H2O system. Auger spectroscopic analyses with depth profiling indicate a titanium oxide layer, whose thickness depends on current density, acts as a precursor to BaTiO3. Use of highly oxidizing atmospheres promotes the formation of thick, well-crystallized and electrically insulating films of BaTiO3 at low temperatures. Films synthesized at 55'C exhibit a characteristic bilayer structure consisting of a large grained porous top layer above a fine grained and dense bottom layer. In contrast, the films prepared at higher temperatures are uniform, fine grained but porous. Preliminary experiments indicate the feasibility to electrochemically synthesize BaTiO3 at temperatures near 25°C.
Modeling of Hysteresis Properties of Lead Zirconate Titanate Thin Films
Authors: Yoo In K. , Desu Seshu B. 
Published: March 2011

AbstractIt is proposed that the polarization reversal mechanism in ferroelectric ceramics such as titanates is controlled by nucleation, growth, merging and shrinkage of ferroelectric domains. These domain phenomena are in turn determined by the nature of Barkhausen jumps, internal electric field, and dielectric relaxation times of the dipoles. Based on the proposed polarization reversal mechanism, a quantitative model was developed for simulating the hysteresis properties of lead zirconate titanate (PZT) thin films. The simulated hysteresis loops are in good agreement with the experimental results.It was observed that dielectric viscosity, which is very useful in understanding fatigue and aging behavior of PZT thin films, is one of the key parameters that controls the hysteresis properties.
Crystallization Dynamics and Rapid Thermal Processing of PZT Thin Films
Authors: Chen Jiayu , Brooks Keith G. , Udayakumar K.R. , Cross L. Eric 
Published: March 2011

AbstractThe crystallization process of PZT thin films has been studied in situ by means of Environmental Scanning Electron Microscopy ( ESEM ). Based on the ESEM observations, the Rapid Thermal Processing (RTP) technique has been employed to crystallize ferroelectric thin films. Various annealing temperature-time combinations were investigated; the results indicate the crystallization process to be very fast. X-ray diffraction data shows the crystallization to be complete in 10 seconds at 600°C, and in 1 second at 700°C. In comparison with conventionally furnace processed films, the RTP films have comparable ferroelectric and dielectric properties, but are distinguished by superior breakdown strengths and morphologically smoother surface. The relation between microstructure of films and crystallizing parameters has been studied.