bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-Quality InGaAsP Crystals Grown by MOVPE Using TBA and TBP
Authors: Kuramata A. , Yasmazaki S. , Nakajima K. 
Published: March 2011

ABSTRACTTBA and TBP are attractive candidates for group V sources for MOVPE growth from the viewpoint of safety. We studied how the composition of InGaAsP crystals depends on growth conditions, and investigated its electrical and optical properties. The relationship between group V sources and crystals indicates that TBA and TBP decompose into AsH and PH. Since there is no carbon in AsH and PH, carbon contamination in the crystals is expected to be small. Carrier concentrations ranged from 5×1014 cm−3 to 1.5×1015 cm−3. Photoluminescence spectra at 4.2K showed strong band-edge emission with no acceptor-related emission. Based on the electrical and optical properties of the crystals, we conclude that high-quality InGaAsP crystals can be grown using TBA and TBP.
Peculiarities of the Far-Infrared Reflection Spectra of the Doped Lead-Tin Tellurides Revealing the Persistent Photoconductivity Effect
Authors: Belogorokhov Aleksander I. , Ivanchik Ivan I. , Khokhlov Dmitriy R. , Popovich Zoran V. , Romchevich Nebojsha 
Published: March 2011

ABSTRACTWe measured the far-infrared reflectivity spectra of PbTe(Ga) and Pb1−xSnxTe(In) - materials revealing the Persistent Photoconductivity effect at the low temperatures T<Tc; Tc≈80K and 25K, respectively-The reflectivity spectra display the singuliarity nearby the plasmon-phonon minimum. The spectra may be fitted satisfactory by means of the introduction of an additional oscillator into the dispersion relation. The result is interpreted in the framework of the model taking into account the temperature change of the one-electron metastable impurity state Position in the configuration-coordinate space. The oscillator corresponds to the two-electron - one-electron state transitions. Some previously unexplained results find the satisfactory interpretation in the framework of the model Proposed.
Structure and Properties of WNx Thin Film on GaAs Substrate
Authors: Mao Dali , Yu Weili , Lin Dongliang , Lin T.L. 
Published: March 2011

ABSTRACTIn this paper, the effect of sputtering parameters on the interfacial reaction and the electronic properties of the WNx system were reported.The report showed that W and W2 N phases were observed in WNx film on GaAs substrate annealed at 800–900°C, in which no UN phase was found and W2N was the stable phase. Throughout the WNx film, W,N distributed uniformly. There was no interdiffusion between WN, films and GaAs substrate annealed at 80°C. However, at 900°C, there was some N in-diffusion to substrate, but no Ga or As out-diffusion. The electrical resistivity p of WNx films increased with increasing nitrogen partial pressure r. All the samples with r<0.2 showed the p below 200 µΩcm. By the I/V measurement, the Schottky Barrier Height was obtained with the value: øB=0.93ev, n=1.30 for WNx/n-GaAs contact that annealed at 850°C, 15 minutes.
Effect of Substrate Orientation on CdTe Film Growth by OMVPE
Authors: Snyder D.W. , Ko E.I. , Mahajan S. , Sides P.J. 
Published: March 2011

ABSTRACTMost CdTe epilayers grown by OMVPE have been deposited on two low index orientations: {111}Te and {100}. In this study we have examined the OMVPE of CdTe as a function of deposition temperature on CdTe substrates having the four low index orientations ({111}Te, P111}Cd, {110}, and {100}) and on the {211}Te and {211}Cd orientations. Results are presented for deposition rate, surface morphology, and structural quality of the epilayers.
Near Ir Emissions from Er, Tm, AND Pr Implanted GaAs and AlGaAs
Authors: Pomrenke G.S. , Yeo Y.K. , Hengehold R.L. 
Published: March 2011

ABSTRACTOptical properties of Er, Tr, and Pr ion implanted GaAs and A1xGa1−xAs were investigated using photoluminescenoe. For Er, the characteristic sharp emissions around 1.54 μm were observed at sample temperatures as high as 296 K, which are due to the transitions between the weakly crystal-field-split spin-orbit levels 4I13/2 and 4I15/2 of Er3+ (4f11) ; the strongest luminescence signal was from A10.4Ga0 6As. For Tm, the sharp 4f-emissions were observed between 1.22 to 1.33 μm at sample temperatures up to 200 K, and are due to the transitions between levels 3H5 and 3H6 of Tm3+ (4f12). For Pr, three sets of 4f-emissions were observed at 1.05, 1.35, and 1.6 μm due to transitions between levels 1G4∼3H4, 1G4∼3H5, and 3F3 ∼ 3H4 of Pr3+(4f2), respectively, and the highest temperature at which sharp emissions were observed was around 175 K.
II-VI Semiconductor Heterostructures: Pointers to Appropriate Analysis Techniques
Authors: Bithell Erica G. 
Published: March 2011

ABSTRACTApproximate methods are used, for a variety of II–VI semiconductor alloys, to estimate the sensitivity to composition change of quantitative transmission electron microscopy techniques which have proved successful in characterising III–V heterostructures. It is shown that bright field thickness fringe matching at the [001] axis is likely to prove relatively more successful than 200 dark field intensity measurement for many alloy systems. It is also noted that alternative methods would be necessary if quantitative characterisation of (Mn,Zn) compounds were required.
In Situ Spectroscopic Ellipsometry for Real Time Semiconductor Growth Monitor
Authors: Johs Blaine , Meyer Duane , Cooney Gerald , Yao Huade , Snyder Paul G. , Woollam John A. , Edwards John , Maracas George 
Published: March 2011

ABSTRACTA modular spectroscopic ellipsometer for in situ and ex situ materials analysis is described, and results for in situ MBE growth of GaAs/AlGaAs are reported.
Thermoelectric Power in Quantum Confined Bismuth Under Classically Large Magnetic Field
Authors: Ghatak Kamakhya P. , Biswas S. N. 
Published: March 2011

ABSTRACTIn this paper we studied the thermoelectric power under classically large magnetic field (TPM) in quantum wells (QWs), quantum well wires (QWWS) and quantum dots (QDs) of Bi by formulating the respective electron dispersion laws. The TPM increases with increasing film thickness in an oscillatory manner in all the cases. The TPM in QD is greatest and the least for quantum wells respectively. The theoretical results are in agreement with the experimental observations as reported elsewhere.
On the Photoemission from Ternary and Quaternary Alloys Systems Under Strong Magnetic Quantization
Authors: Ghatak Kamakhya P. 
Published: March 2011

ABSTRACTWe study the photomission from ternary and quanternary alloys systems by formulating the respective expressions considering the spin & broadening of Landau levels. It is found taking n-Hg1−x CdxTe and In1−xGaxAsyP1−y lattice matched to InP as examples of ternary and quaternary alloys respectively that the photoemission exhibits oscillatory magnetic field dependence and increases with increasing electron concentration in spiky manner for both the cases. The numerical magnitudes of photoemission in ternary alloys are greater than that of the quaternary systems and the theoretical formulations are in agreement with the experimental observations as reported elsewhere.
Micro-Ellipsometric Measurements of Strained Layer Structures
Authors: Xiong Yi-Ming , Snyder Paul G. 
Published: March 2011

ABSTRACTEllipsometric measurements are extremely sensitive (on the monolayer scale) to layer thicknesses and surface or interfacial roughness. However, lateral resolution is poor, because of the need for a highly collimated ( ≤0.05° ) and therefore large diameter (typically 1 mm) optical beam. Many materials are inhomogeneous on a smaller lateral scale, in which case conventional ellipsometry simply measures some average value. Focusing the beam leads, for an incoherent light source, to an uncollimated beam and a consequential spread in the angle of incidence, which in turn degrades the sensitivity. We describe here a technique for focusing a coherent, Gaussian laser beam to a minimum spot size of about 30μm × 130μm, while maintaining a negligible effective spread in angle of incidence. The technique was used to measure semi-insulating (S.I.) GaAs, laser annealed ion implanted GaAs, and InIGa1−xAs strained layer structures.
Ion Milling Damage in InP and GaAs
Authors: Pearton S. J. , Chakrabarti U. K. , Perley A. P. 
Published: March 2011

ABSTRACTNear-surface damage created by Ar+ ion milling in InP and GaAs was characterized by capacitance-voltage, current-voltage, photoluminescence, ion channeling and transmission electron microscopy. We find no evidence of amorphous layer formation in either material even for Ar+ ion energies of 800eV. Low ion energies (200eV) create thin (≤100 Å) damaged regions which can be removed by annealing at 500°C. Higher ion energies (≤500 eV) create more thermally stable damaged layers which actually show higher backscattering yields after 500°C annealing. Heating to 800°C is required to restore the near-surface crystallinity, although a layer of extended defects forms in GaAs after such a treatment. No dislocations are observed in InP after this type of annealing. The electrical characteristics of both InP and GaAs after ion milling at ≥500 eV cannot be restored by annealing, and it is necessary to remove the damaged surface by wet chemical etching. For the same Ar+ ion energies the damaged layers are deeper for InP than for GaAs-after 500 eV ion milling at 45° incidence angle, removal of ∼485 Å and ∼650 Å from GaAs and InP respectively restores the initial current-voltage charaeteristics of simple Schottky diodes.
Traps and Trap-Assisted Tunneling in HgCdTe Photodiodes
Authors: Rosenfeld D. , Bahir G. 
Published: March 2011

ABSTRACTThe performance of HgCdTe photodiodes, realized for the purpose of thermal imaging in the 8–12μm atmospheric window, is often limited by traps and by the tunneling mechanism associated with them. This mechanism dominates the leakage current and the dynamic resistance in diodes operated in reverse bias above 1OOmV and at temperatures below 77K. In usual working conditions, namely low reverse bias and a temperature of 77K, the presence of traps and the tunneling mechanism associated with them, degrades the performance of the diodes. Although the diffusion mechanism dominating the leakage current and the dynamic resistance in diodes operated under the above conditions is of major concern, the presence of the traps should not be ignored. The traps result in shorter electron lifetime in the bulk as well as in the generation of 1/f noise, which degrades the device's figures of merit such as NETD. Therefore, a thorough understanding of the trapassisted tunneling mechanism is a prerequisite to studying its impact on the device performance.In this paper we present a model which describes the connection between the leakage current associated with the traps and the trap characteristics: concentration, energy level and capture cross-section. The validity of the model is confirmed by the good fit between measured and calculated characteristics of the diodes.
Three-Dimensional Nuclear Magnetic Resonance and X-Ray Microtomographic Imaging of Composite Materials
Authors: Dieckman S.L. , Rizo P. , Gopalsami N. , Botto R. E. 
Published: March 2011

ABSTRACTThis paper presents a new, three-dimensional (3-D) nuclear magnetic resonance (NMR) imaging technique for spatially mapping proton distributions in green-state ceramic composites. The technique is based on a 3-D back-projection protocol for data acquisition, and a reconstruction technique based on 3-D Radon transform inversion. In principle, the 3-D methodology provides higher spatial resolution of solid materials than is possible with conventional slice-selection protocols. The applicability of 3-D NMR imaging has been demonstrated by mapping the organic additive distribution (2.5 wt.%) in cold-pressed Si34 whisker-reinforced Si34 ceramic composites. Three-dimensional X-ray computed tomography (CT) also has been employed for mapping voids and inclusions within the composite specimen. Combining information from both imaging modalities provides an extremely powerful nondestructive evaluation tool for materials characterization.
Characterization of Low Density Carbon Foams by X-ray Computed Tomography (CT) and Ion Microtomography (IMT)
Authors: Moddeman W. E. , Kramer D. P. , Firsich D. W. , Trainer P. D. , Yancy R. N. , Weirup D. L. , Logan C. M. , Pontau A. E. , Antolak A. J. , Morse D. H. 
Published: March 2011

ABSTRACTTwo NDT techniques were used to characterize low-density, microcellular, carbon foams fabricated from a salt replica process. The two techniques are x-ray computed tomography (CT) and ion microtomography (IMT); data are presented on carbon foams that contain high-density regions. The data show that densities which differ by <10% are easily observable for these low density (<100 mg/cm3) materials. The data reveal that the carbon foams produced by this replica process have small density variations; the density being ∼30% greater at the outer edges than when compared to the interior of the foam. In addition, the density gradient is found to be rather sharp, that is the density drops-off rapidly from the outer edges to a uniform one in the interior of the foam. This edge build-up in carbon density was explained in terms of polymer concentrating on the foam exterior during drying which immediately followed a polymer infusion processing step. Supporting analytical data from other techniques show the foam material to be >99.9 % carbon
NMR Imaging of Elastomers and Porous Media
Authors: Komoroski Richard A. , Sarkar Subhendra N. 
Published: March 2011

ABSTRACTNMR imaging has been applied to some elastomeric materials of industrial interest. The T2s of common elastomers, Particularly after filling and curing, are sufficiently short That spin-echo sequences at submillisecond echo times cannot Produce T2 independent images. The sensitivity to T2 Potentially makes spin echo imaging a good probe of elastomer Blend composition, as demonstrated for a series of filled and Cured cis-polybutadiene, styrene-butadiene rubber blends. The Technique can be used to distinguish good and bad carbon black Dispersion in actual tire tread samples. The configuration of Polyester tire cord, voids, rubber layer boundaries, differences of molecular mobility and composition, and other inhomogeneities can be detected in end-product tire samples. The value of isotropic voxels at 80–100 um and the effect of resolution Relative to pore size are demonstrated on a model, H2O-saturated Porous glass disk of 200-um average pore size. The feasibility of multinuclear NMR imaging for fluid-specific characterization of porous materials such as oil cores is demonstrated for 7Li and 19F
Development of Quantitative X-Ray Microtomography
Authors: Deckman H. W. , Dunsmuir J. H. , D'Amico K. L. , Ferguson S. R. , Flannery B. P. 
Published: March 2011

ABSTRACTWe have developed several x-ray microtomography systems which function as quantitative three dimensional x-ray microscopes. In this paper we describe the evolutionary path followed from making the first high resolution experimental microscopes to later generations which can be routinely used for investigating materials. Developing the instrumentation for reliable quantitative x-ray microscopy using synchrotron and laboratory based x-ray sources has led to other imaging modalities for obtaining temporal and spatial two dimensional information.
Temperature Dependent Defect Density Calculated from Activated Conductivity of a-Si:H
Authors: Drusedau T. , Kirbs V. , Fiedler H. 
Published: March 2011

ABSTRACTThermally activated conductivity of a—Si:H at a slow cooling rate of 0.3 K/min is connected with temperature dependent changes of the mobility gap states. By means of the Fermi—level shift calculated from these data and a density of states model it is possible to determine this dependence. The results mainly reveal a decrease of the defect state density by about a tenth between 375 K and 400 K.
Defect Creation by Forward Bias in Amorphous Silicon P-I-N Diodes
Authors: Street R. A. , Hack M. 
Published: March 2011

ABSTRACTMetastable defects are induced in a-Si:H p-i-n devices by a forward bias current. The defect density increases approximately as the square root of time, reaching saturation at long inducing times, and with a weak temperature dependence. Current-induced defect annihilation is observed, in which the current causes a reduction in the previously induced defect density. Calculations of the changes in the forward bias current for different bulk defect densities are able to account for the measured results.
Metastable Defects in a-SiOx:H and a-SiCx:H
Authors: Deng X.-M. , Hamed A. , Fritzsche H. , Tran M. Q. 
Published: March 2011

ABSTRACTMetastable defects are created in hydrogenated amorphous silicon alloys presumably by the same mechanism as in a-Si:H. We find metastable defects created in a-SiCx:H and a-SiOx:H by hopping injection of photocarriers from adjacent a-Si:H layers. In a-SiCx:H the defects can be created only below T=150K, they anneal at TE=400K. In a-SiOx:H they are created at or below T=300K, they anneal at TE=480K. The anneal temperature is nearly independent of the creation temperature. The defects are detected by their charge exchange with adjacent a-Si:H layers whose conductance is thereby changed.
Characterization of A-Si : H and A-SiGe : H Films in Liquid Crystal Light Valve
Authors: Qiao Jianmin , Han Gaorong , Du Piyi , Han Weiqiang , Huang Wanquan , Ding Zishang 
Published: March 2011

ABSTRACTA-Si : H and a-Si : H/a-SiGe : H heterojunctions have been prepared as the photoconductors in the liquid crystal light valves. The impedance matching conditions of the a-Si : H and the heterojunction in the valves have been carefully analysed, which has shown that the adjustment for the capacitance of the photoconductor is the key procedure for the matching, but the low photocapacitance effect in the a-Si : H limits the further improvements on the matching. The formation of the a-Si : H/a-SiGe : H diode promotes the photocapacitance effect in the photoconductor, and the matching behavior in the valve is greatly improved.
Theoretical and Experimental Analysis of Amorphous Silicon Image Sensor
Authors: Su Chih-Yuang , Su Ying-Wen , Hwang Huey-Liang 
Published: March 2011

ABSTRACTThe experimental results for different structures of contact image sensor are reported in this paper, which includes Schottky barrier, p-i junction, p-l-n junction, and MIS structures. The J-V characteristics of p-i-n a-Si: H contact image sensor under dark and illuminated conditions have been simulated by solving the Poisson's equation and the continuity equations, and the results are correlated with the experiments. The dependence of the dark and photo currents on the parameters such as the density of states in the gap, intrinsic layer width, dopant concentrations of p* layer and n+ layer are discussed.
Characteristics of a-Si:H Schottky Photodiode by Using Mo Barrier Metal at Al/ITO Contact
Authors: Sakai Yoshihiko , Hotta Hiroyuki , Hamada Tsutomu , Ito Hisao , Ozawa Takashi 
Published: March 2011

ABSTRACTAn ITO/a-Si:H Schottky Photodiode(PD) with Mo as a barrier metal at Al/ITO contact has been made and it shows its useful characteristics. The PD without Mo had high dark current proportional to the contact-via-hole area and quite a large resistance at the contact area. The XPS analysis of the Al/ITO interface indicated that Al and O in ITO mutually diffused around the interface, resulting in the degradation of ITO/a-Si:H Schottky barrier. Most of the diffused Al formed aluminum oxide (AI2O3) at the Al/ITO interface, and which caused high resistance of the contact area.Inserting Mo barrier metal 500Å thick, the dark current got less dependent on the contact area and decreased by 2/3 on 254×227 μm PD with 106×106//m contact-via-hole. The contact resistance also decreased significantly to 1/105 of those of the conventional ones. From the XPS analysis of interface, it was also found that Mo barrier metal prevented Al diffusion into the ITO and formation of aluminum oxide at the interface.
Results from First Principles Molecular Dynamics Simulations on a-Si
Authors: Fedders Peter A. , Drabold David D. 
Published: March 2011

ABSTRACTWe report on some recent results of first principles molecular dynamics simulations on a-Si. These simulations yield interesting results that challenge the standard beliefs about what constitutes a defect, how light induced defects arise, and about the origins of conduction band tailing.
Effects of Annealing Time and Temperature on Hydrogen in Doped and Intrinsic Amorphous Silicon
Authors: Ready S. E. , Boyce J. B. 
Published: March 2011

ABSTRACTThe local environment and diffusion of hydrogen in hydrogenated amorphous silicon (a-Si:H) depend on both temperature and doping. Previous studies of hydrogen evolution indicate that the manner in which hydrogen diffuses and desorbs from the material depends on doping and may occur at relatively low temperatures over extended time frames. We have examined the microstructure of hydrogen in intrinsic, boron doped and phosphorous doped a-Si:H as a function of annealing temperature and annealing time using hydrogen NMR. Changes in both the H NMR spectrum and spin-lattice relaxation times occur. We find annealing time has only a small effect on these parameters, whereas the annealing temperature has a substantial effect. The bonded-H content drops and the molecular-H2 content is seen to decrease slightly as the samples are annealed to higher temperatures. However the bonded-H remains essentially constant for long time, low-temperature anneals, while the molecular-H2 content is also seen to diminish slightly. The changes are more profound for B-doped samples than for P-doped or intrinsic material, consistent with the conclusions of other studies.
In Situ IR Absorption Study of H Bonding in a-Si:H Thin Films
Authors: Katiyar M. , Feng G. F. , Abelson J. R. , Maley N. 
Published: March 2011

ABSTRACTWe have used real time, in situ infrared reflectance spectroscopy to study the evolution of Si-H bonding during the growth of hydrogenated amorphous silicon (a-Si:H) by dc magnetron reactive sputtering. The surface Si-H stretching mode (2100 cm-l) is observed in films 5 Å thick and the 2000 cm-l mode, which has been attributed to isolated monohydrides in the bulk, appears for thickness (d) < 10–15 Å For larger thicknesses the intensity of both modes increases approximately linearly. These trends are interpreted in terms of the nucleation and coalescence of islands for d> 15 Å followed by bulk-like growth.
Lattice Relaxation of Deep Defects in Light-Soaked N-Type Hydrogenated Amorphous Silicon
Authors: Leen Thomas M. , David Cohen J. 
Published: March 2011

ABSTRACTWe report evidence for a deep defect exhibiting very large lattice relaxation in n-type a-Si:H. In light-soaked partially-annealed samples with low phosphorus doping levels one obtains large controlled variation of the Fermi energy position in the mobility gap. Examination by photocapacitance spectroscopy of a sample having a Fermi energy near the minimum in the density of states shows dramatic change in the shape of the photocapacitance spectra. We interpret this as strong evidence for lattice relaxation of deep defects.
Excimer Laser Crystallized Amorphous Silicon Films: Effects of Shot Density and Substrate Temperature
Authors: Johnson R. I. , Anderson G. B. , Ready S. E. , Boyce J. B. 
Published: March 2011

ABSTRACTLaser crystallization of a-Si thin films has been shown to produce materials with enhanced electrical properties and devices that are faster and capable of carrying higher currents. The quality of these polycrystalline films depends on a number of parameters such as laser energy density, shot density, substrate temperature, and the quality of the starting material. We find that the average grain size and transport properties of laser crystallized amorphous silicon films increase substantially with laser energy density, increase only slightly with laser shot density, and are unaffected by substrate temperatures of up to 400°C. The best films are those processed in vacuum but films of fair quality can also be obtained in air and nitrogen atmospheres.