bluuebunny/crossref_metadata_2025_split huggingface dataset:
Convection in Pulsed Laser Formed Melts
Authors: Possin G. E. , Parks H. G. , Chiang S. W. 
Published: March 2011

ABSTRACTIn this paper we treat surface tension driven convection effects in pulsed laser formed melts. Mass transport is determined from an approximate solution of the Navier Stokes equation. It is shown that for small laser spot diameters the characteristic mixing times are on the order of 100's of ns. The dependence of the convection mechanism on material and laser parameters is discussed and extended to thin metal films on Si. Experimental results substantiating the theoretical considerations are presented.
Measurement of Phase Boundary Dynamics During Scanned Laser Crystallization of Amorphous Ge Films
Authors: Chapman R. L. , Fan John C. C. , Zeiger H. J. , Gale R. P. 
Published: March 2011

ABSTRACTTwo techniques have been used to measure the velocity of the amorphous-crystalline boundary during scanned laser crystallization of amorphous Ge films on fused-silica substrates. Values in the vicinity of 200 cm sec-1 have been measured by both methods. The results obtained by the first technique, an optical transmission method, confirm our theoretical model for the periodic motion of the boundary. The measurements made by the second technique, which is based on an examination of the structural features obtained at laser scanning rates up to about 600 cm sec-1 , show the boundary velocity to be rather insensitive to film thickness and background temperature. Controlled crystallization is expected to require stability of the laser beam power.
Explosive Crystallization of Amorphous Germanium Films
Authors: Leamy H. J. , Brown W. L. , Celler G. K. , Foti G. , Gilmer G. H. , Fan J. C. C. 
Published: March 2011

ABSTRACTLaser processing of amorphous thin films of amorphous Ge often results in an explosive or self-sustaining crystallization reaction. The reaction is sustained by the heat liberated during crystallization. In a theoretical analysis of the process that was presented at this symposium last year, Gilmer and Leamy postulated the existence of a thin layer of liquid at the propagating interface. The liquid layer forms at temperatures above Ta, the melting point of amorphous Ge, and is predicted to be ~ 0.02 – 0.1 of the film thickness in width. We have obtained experimental confirmation of the presence of this liquid layer.
Thin-Film Gd4 Bi3 Grown on a Glass Substrate
Authors: Baba Kyuya , Ishii H. , Yamaguchi I. , Nakamura O. , Takeda T. 
Published: March 2011

ABSTRACTSputtered thin-films of Gd-Bi (4:3 in atomic ratio) were annealed in vacuum under various annealing conditions. The samples annealed at a temperature near 530°C and 4 hours contained 40% of poly-crystalline Gd4Bi3 phase, which is of the anti-Th3P4 structure. The main peak in the x-ray diffraction spectrum due to Gd4Bi3 is of (310). The phase of Gd4Bi3 was not found for a lower annealing temperature; for a higher annealing temperature (above 550°C), this phase could not be observed, because other phases or structures were beginning to grow, e. g. Gd5Bi3 and/or GdBi phases.The Curie temperature of the Gd4Bi3 thin-films was estimated to be about 330 K; this value is nearly the same as that of bulk Gd4Bi3. The residual resistance of the Gd4Bi3 thin-films was several times as large as that of bulk Gd4Bi3 poly-crystal.
Pseudomorphic ZnTe/AlSb/GaSb Heterostructures by Molecular Beam Epitaxy
Authors: Mathine D.L. , Han J. , Kobayashi M. , Gunshor R.L. , Menke D.R. , Vaziri M. , Gonsalves J. , Otsuka N. , Fu Q. , Hagerott M. , Nurmikko A.V. 
Published: March 2011

ABSTRACTA series of pseudomorphic ZnTe/AlSb/GaSb epilayer/epilayer heterostructures, aimed at the realization of novel wide bandgap light emitting devices, were grown by molecular beam epitaxy. The low temperature photoluminescence (PL) spectra of ZnTe epilayers showed dominant near-band-edge features related to free, and shallow impurity bound excitons. The PL could be seen at room temperature. Both GaSb and AlSb were doped n-type using a PbSe source.
Properties of Chlorine-Doped Zinc Selenide Grown by Molecular Beam Epitaxy
Authors: Hwang S. , Ren J. , Bowers K.A. , Cook J.W. , Schetzina J.F. 
Published: March 2011

ABSTRACTZnSe:Cl epilayers have been grown on (100) GaAs by MBE using a Zn to Se beam flux ratio of 2:1 and substrate temperatures as low as 225 °C. The ZnSe:Cl epilayers are highly conducting and exhibit bright blue-violet edge luminescence at 300 K. A mobility of 2480 cm2 /V-s at 40 K was measured for an n-type ZnSe:CI film that was Cl-doped to ∼2.3×1017 cm−3 and for which a compensation ratio (NA/ND) of ∼3% was calculated. Carrier concentrations as large as 6.7×1018cm−3 were obtained by increasing the temperature of the MBE oven containing the C1 dopant.
Surface Morphology and Photoluminescence Spectra of ZnSe (Na) After Excimer Laser Annealing
Authors: Yi Guan-Jiun , Neumark G F. , Lu Z. , Newiury P.R. , Yu C.F. , Fitzpatrick B.J. , Shone M. , Sicignano A. 
Published: March 2011

ABSTRACTWe have investigated excimer laser annnealing of Na doped ZnSe, with emphasis on photoluminescence (PL) characterization as a probe of resultant changes in materials properties. We observed a relative increase, after annealing, of Na on substitutional (acceptor) sites vs. Na on interstitial (donor) sites. Another result was the occurrence of extensive twinning; unfortunately such twinning has complicated the analysis of other changes.
Photoluminescence Properties of Graded Composition MgxZn1−xSe Crystals
Authors: Lozykowski H. J. , Jiang X. D. , Merz J. L. , Barbara S. 
Published: March 2011

ABSTRACTThe photoluminescence properties of MgxZn1−xSe solid solution grown on ZnSe substrate by a closed solid-state diffusion technique have been investigated. The depth profiles of the diffusion region shows distinguished surface layer and thick graded layer. The PL. spectra of MgxZn1−xSe side of the sample excited with a wide range of excitation energy shift the edge emission band toward longer wavelengths with decreasing excitation energy. The edge emission spectrum was found to shift toward the shorter wavelength with electric field applied parallel to the compositional gradient ofMgxZn1−xSe-ZnSe heterostructure.
Growth of Lattice-Matched ZnSe-ZnS Strained-Layer Superlattices Onto GaAs as An Alternative to ZnSSe Alloys
Authors: Oniyama H. , Yamaga S. , Yoshikawa A. 
Published: March 2011

ABSTRACTThis paper describes the results of the first attempt to reduce misfit dislocations in epilayers of a wide bandgap II-VI semiconductor on GaAs substrates by utilizing the ZnSe-ZnS strained-layer superlattice (SLS) structure. From a theoretical calculation, SLSs consisting of a 200A-ZnSe and a IOA-ZnS layer in one period can be grown as lattice-matched films to GaAs substrates. It has been found from the photoluminescence measurements and electron-beam-induced-current (EBIC) image observations that the generation of misfit dislocations can be markedly reduced, as expected.
Optical Properties of CdZnS-ZnS Strained-Layer Superiattices
Authors: Endoh Yasuyuki , Taguchi Tsunemasa 
Published: March 2011

ABSTRACTThe Cd0.3 Zn0.7S-ZnS strained-layer superlattices has for the first time been fabricated on (100)GaAs substrates by a low-pressure MOCVD method. Exciton luminescence properties were investigated by the photoluminescence spectroscopies which show that the quantum confinement effect of excitons occurs in the CdZnS alloy layer. Temperature dependence of the exciton properties reveals a dominant scattering process which originates from exciton-phonon interaction(Γ10 =68meV). Nevertheless, the large exciton binding energy of about 166meV makes it possible to produce the exciton peak at room temperature. The effect of external electric field on the exciton intensity and its peak position is found and is tentatively interpreted in terms of a quantum confined Stark effect.
Precise Measurements of Transient Excess Carrier Lifetimes in II-VI Films and Superlattices
Authors: Doggett W. O. , Thelander Michael W. , Schetzina J. F. 
Published: March 2011

ABSTRACTA system has been developed for accurately measuring lifetimes for photo-induced excess current carriers in semiconductors using the transient photoconductivity decay method. The specifications of state-of-the-art equipment, considerations peculiar to the capture of fast transient pulses, and sophisticated statistical data analysis techniques are discussed. Experimental results are presented to demonstrate the capability of the system (a) to measure lifetimes in the 40-ns - 75-µs range for temperatures varying from 77K to 300K with 10% accuracy for single lifetime decays and 30% accuracy for individual effective lifetimes in a multi-component decay, and (b) to use a 300-ns lifetime photoconductor as a detector to measure nanosecond-time-scale structure of laser pulses. The predominant excess carrier lifetimes of HgCdTe samples grown at NCSU by photoassisted molecular beam epitaxy (PAMBE) ranged from 46 ns at 300K to 341 ns at 77K. CdTe samples and CdMnTe-CdTe superlattices exhibited a multi-component decay with the two longest components having effective lifetimes of 26 µs and 4 µs for CdTe and 75 µs and 10 µs for CdMnTe-CdTe. These values were relatively insensitive to temperature variation.
Growth and Initial Characterization of Novel Hgte-Based II-VI Materials
Authors: Moore F.G. , Abele J.C. , Kremer R.E. 
Published: March 2011

ABSTRACTHg1−xAxTe materials where A= {Be, Mg, Ba, Sr, Ca} have been synthesized by the vertical Bridgman technique. Hydrostatic density measurements showing segregation are presented and for HgMgTe an effective segregation coefficient is obtained. For HgMgTe a relationship between bandgap E and composition x, is developed based on FTIR measurements of cut-on wavelengths. The variation of energy gap with composition is found to be comparable to that of HgMnTe and twice as rapid as that of HgCdTe. Carrier concentration and mobility data from room temperature and 77K Hall measurements are presented for samples annealed in a saturated overpressure of Mercury.
Electrical Properties of Mbe-Grown HgCdTe
Authors: Hwang S. , Schetzina J.F. 
Published: March 2011

ABSTRACTA detailed analysis of Hall data obtained at temperatures between 20K and 300K has been made for n-type HgCdTe epilayers prepared by molecular beam epitaxy (MBE). Based on a theoretical calculation for intrinsic concentrations that takes into account the non-parabolicity of the conduction band, the electron concentrations are shown to follow nicely the model for semiconductors in their intrinsic and extrinsic ranges. The scattering mechanisms in these materials are studied through the analysis of electron mobility. Polar mode phonon scattering, acoustic mode via deformation-potential coupling, acoustic mode via piezoelectric coupling, and impurity scattering are included in the mobility calculation. The results indicate that these mechanisms are insufficient to explain the measured mobility.
Photoluminescence Detection of Native Defects in The Surface Region of Bulk CdTe
Authors: Amirtharaj P.M. , Dhar N.K. 
Published: March 2011

ABSTRACTThe native defects introduced by Br2/CH3 OH etching and aging under atmospheric conditions have been investigated in In doped, bulk CdTe using photoluminescence (PL) spectroscopy. The results indicate a large enhancement of the Cd vacancy related 1.5896 eV excitonic feature with chemical treatment and aging. Hence, the primary perturbation is interpreted to be a small loss of Cd within the sampling region. This result is compared and contrasted with previous studies of etching induced modifications. The implications of Cd depletion on interpreting PL spectra, device processing and long term stability are considered.
Surface Electrons in Inverted Layers of p-HgCdTe
Authors: Schacham Samuel E. , Finkman Eliezer 
Published: March 2011

ABSTRACTAnodic oxide passivation of p-type HgCdTe generates an inversion layer. Extremely high Hall mobility data for electrons in this layer indicated the presence of a two-dimensional electron gas. This is verified by use of the Shubnikov-de Haas effect from 1.45-4.15K. Data is extracted utilizing a numerical second derivative of DC measurement. Three sub-bands are detected. Their relative occupancies are in excellent agreement with theory and with experimental results obtained on anodic oxide as accumulation layers of n-type HgCdTe. The effective mass derived is comparable to expected.
Surface Roughness Theory and Low-Temperature Epitaxy
Authors: Krishnamurthy Srinivasan , Berding M.A. , Sher A. , Chen A.-B. 
Published: March 2011

ABSTRACTA single-and multilayer growth model is presented. Surface order-disorder transitions are studied with the entropy calculated in the Bragg-William approximation and in the quasi-chemical approximation. A plausible explanation for high-quality growth obtained with energy-assistance is given. The model has been extended to study low-temperature epitaxial growth of HgTe and CdTe on different surfaces. The relevant surface energies are evaluated in a Green's function approach.
Enhanced Metallization Stability on Mercury-Cadmium-Telluride
Authors: Raisanen A. , Haugstad G. , Yu X. , Ceccone G. , Franciosi A. 
Published: March 2011

ABSTRACTSynchrotron radiation photoemission studies of ultra-thin Yb diffusion barriers at the interface between Mercury-Cadmium-Telluride semiconductors and Ag overlayers show that the interlayers act as effective diffusion barrier only after thicknesses of 10-15 Å are reached. Studies of interlayer morphology by means of photoemission from physisorbed Xe indicate that effective diffusion barriers are consistent with a model in which a continous Yb-Te reacted layer is covered by an Yb-rich layer with high alloying enthalpy for Hg.
Growth of Large-Diameter CdZnTe and CdTeSe Boules for Hg1−xCdxTe Epitaxy: Status and Prospects
Authors: Sen S. , Johnson S.M. , Kiele J.A. , Konkel W.H. , Stannard J.E. 
Published: March 2011

ABSTRACTSingle crystals of CdTe or dilute alloys of Cd1−yZnyTe (y ≤ 0.04) and CdTe1−zSez (z ≤ 0.04) with low defect density and large single-crystal area (>30 cm2) are required as substrates for high-quality epitaxial Hg1−xCdxTe thin films in the infrared (IR) detector industry. Bridgman or gradient freeze has been the most common current technique used for growing these materials. This paper reviews the current status and the evolution at SBRC of one variation of the Bridgman technique, viz., vertical-modified Bridgman (VMB), for producing large-area substrates with excellent uniformity and reproducibility. CdTe, Cd1−yZnyTe (y ≤ 0.04) and CdTe1−zSez (z ≤ 0.04) boules of 5-to 7.5-cm diameter have been grown unseeded in the present version of the VMB growth system. In general, under optimum growth conditions, the boules have the smallest grain structure (several grains) at the tip end with enhancement of grain selection as the cylindrical body of the boule is approached, resulting in one predominant and large grain occupying 70 to 80 percent of the entire boule volume; {111}-oriented Cd1−yZnyTe and CdTe1−zSez substrates with single-crystal areas as large as 50 to 60 cm2 have been obtained from these boules. Crystal quality characterized by x-ray rocking curve, IR transmission (2.5 to 20 µm), low-temperature photoluminescence, and Hall-effect measurements as a function of temperature, showed a strong correlation with the starting material quality (especially that of elemental Te and Se). Analyses of the thermal history during growth reveals that the presence of the ampoule (with charge) increases the temperature inside the furnace by 10 to 15 degrees. The temperature gradient at the tip was measured to be 8 to 10°C/cm and it dropped to 4 to 5°C/cm beyond 2.5 cm from the tip - where rapid enhancement of grain selection takes place in most boules. The effect of this temperature rise on the initial crystallization near the tip of a boule can be explained from the numerical thermal model that was developed for the growth process with radiative and conductive heat transfer included and using a temperature profile similar to that existing in the actual growth furnace. Conditions for maximizing the fraction solidifying with a slightly convex interface, hence maximizing the single-crystal yield are discussed.
Growth of High Quality Lwir Films by Liquid Phase Epitaxy
Authors: Chandra Dipankar 
Published: March 2011

ABSTRACTGrowth of long wavelength infra-red mercury cadmium telluride films by liquid phase epitaxy has usually yielded films of inferior electrical properties as evidenced by Hall mobilities lower than theoretical values by factors of 5 or more at 77°K. In addition the Hall behavior over the entire temperature range did not follow classical patterns. A systematic series of investigations was conducted to improve the electrical performance of these films by four methods: i) growth of HgCdZnTe films, where a portion of the cadmium was replaced by zinc, ii) growth at temperatures > 550°C, iii) growth at a slow rate on a CdZnTe substrate following ‘Cleaning’ in the melt of the substrate surface and iv) doping the film by controlled levels of indium. The first method did not lead to any improvements in the Hall behavior. In addition, the films grown displayed varying dislocation densities. The second method led to a small but definite increase in the yield of non-anomalous or classical films (5%). The third method yielded films with classical or non-anomalous Hall behavior about 20% of the time. The last method consistently led to films with classical Hall behavior. This was accomplished with indium doping levels at 1.5× 1014/cm3. Preliminary data indicate that it will be possible to go to still lower doping levels while maintaining classical Hall behavior. The improvement in electrical properties of these epifilms can be attributed to the reduction or elimination of type inhomogeneities known to degrade Hall mobilities in films grown by liquid phase epitaxy.
Effects of Defects on Metal-Insulator-Semiconductor Properties of HgCdTe Films Grown by Liquid Phase Epitaxy
Authors: Chandra Dipankar , Goodwin Michael W. 
Published: March 2011

ABSTRACTA comprehensive study of all materials parameters influencing metal-insulator-semiconductor (MIS) properties of n-type HgCdTe films grown by liquid phase epitaxy from tellurium rich melts was conducted. When the epitaxy process was optimized to grow films free of inclusions and terracing, the first indications of the MIS properties to be expected could be obtained from the temperature dependence of the Hall electron mobility.Films displaying an anomalous dependence of the Hall mobility on temperature yielded non-classical low frequency MIS properties with little or no measurable ‘dark’ storage times (< 2×10−6 second). The MIS performance of these films appeared relatively independent of other materials parameters; remaining, for example, virtually unaffected by the film dislocation density changing between 5×104 and 2 × 106/cm2.Films displaying a classical dependence of the Hall mobility on temperature yielded drastically improved classical high frequency MIS properties. For these films, the MIS performance appeared almost exclusively dependent on dislocation density levels as long as the donor density remained lower than 1×1015/cm3. The dark storage time of classical films increased continuously with decreasing dislocation density levels, rising to 100µsec for a dislocation density level of 1 × 105/cm2 for materials with a 77°K cutoff wavelength of 10.5 µm. A simple monotonic relationship could be established between the MIS performance parameters and the dislocation density over the entire measurement span: from 5×104 to 2.5×106/cm2.
Recent Progress in The Omvpe Growth of HgCdTe
Authors: Ghandhi Sorab K. 
Published: March 2011

ABSTRACTThe last two years has seen rapid development in the growth of mercury cadmium telluride material for use in far infrared detectors. This paper will briefly review the progress before this period, and will focus on recent developments in these materials.The emphasis will be on the direct alloy growth of HgCdTe material by organometallic vapor phase epitaxy (OMVPE).
Structural and Electrical Properties of Heteroepitaxial HgCdTe/CdZnTe/GaAs/Si
Authors: Johnson S.M. , Ahlgren W.L. , Kalisher M. H. , James J. B. , Hamilton W. J. 
Published: March 2011

ABSTRACTThe structural and electrical properties of heteroepitaxial HgCdTe/CdZnTe/GaAs/Si were evaluated using high-resolution x-ray diffraction techniques and Hall-effect measurements as a function of temperature. Significant tilting of the layers was found for both {100} and {111} CdZnTe layers grown on misoriented {100}GaAs/Si substrates, consistent with the interpretation of a low-angle tilt boundary being formed at the interface to relieve the large lattice mismatch between the layers. The GaAs layer is in a state of biaxial tension before and after the growth of the CdZnTe layers. The x-ray FWHM of HgCdTe layers grown by LPE on these substrates was found to be reduced from that of the MOCVD-grown CdZnTe buffer layer due to both an annealing effect during LPE growth and to the increased distance of layer surface from the defective CdZnTe/GaAs interface. Hall-effect mobility for {100}HgCdTe layers was nearly identical to that of layers grown on bulk CdZnTe substrates. High-quality heterojunction infrared detectors have been fabricated using these materials.
Properties of HgTe:ZnTe Strained Layer Superlattices Grown by MOVPE
Authors: Mullins J.T. , Clifton P.A. , Brown P.D. , Hall D.O. , Brinkman A.W. 
Published: March 2011

ABSTRACTHgTe:ZnTe superlattices have been grown by thermal MOVPE at temperatures down to 325°C. At this temperature, interdiffusion is sufficiently low to make superlattice periods as low as 45A practicable. The results of theoretical calculations of the electronic structure of these materials are also reported. These show that the electronic structure may be significantly different to that found for the HgTe:CdTe system due to the large biaxial compression present in the HgTe well layers.
Mbe Growth and Characterization of Lwir HgCdTe
Authors: Lee M.B. , Decarlo J. , Dimarzio D. , Kesselman M. 
Published: March 2011

ABSTRACTWe have grown high-mobility LWIR HgCdTe thin films on CdTe substrates, using molecular beam epitaxy (MBE). The structural, optical, and electrical properties of these epilayers were determined by SEM, DCRC, FTIR, and Hall effect measurements. For films of 10 to 11 µm thick and composition X value ranging from 0.152 to 0.172, the highest mobility observed was 7.5 × 105 cm2 /V-sec, and the FWHMs of the rocking curves were 75 to 110 arcsec. We also have carried out the temperature-dependent EXAFS study of HgCdTe.
Nondestructive Compositional and Defect Characterization of CdZnTe Alloys Using Photoluminescence Spectroscopy
Authors: Duncan W.M. , Koestner R.J. , Tregilgas J.H. , Liu H.-Y. , Chen M.-C. 
Published: March 2011

ABSTRACTResults from high resolution helium temperature photoluminescence (PL) spectroscopy have been correlated to precision lattice constant and transport measurements and to theoretical band gap versus composition behavior. It is found that low temperature PL spectra provide precise determination (+/- 0.02%) of ZnTe mole fraction as well as carrier type, relative impurity concentration and point defect properties of these substrates. In addition helium and room temperature PL results are correlated to determine the accuracy of room temperature measurements for composition determination.
Transport Properties of Narrow Gap II-VI Superlattices
Authors: Hoffman C. A. , Meyer J. R. , Bartoli F. J. 
Published: March 2011

ABSTRACTThe present understanding of the carrier transport properties in Hg-based super-lattices such as the HgTe-CdTe system is reviewed. Novel features in the calculated superlattice band structures and their implications for macroscopic transport properties are discussed. Nearly all of the main experimental results are qualitatively consistent with a large valence band offset, but are difficult to explain if the offset is small. The valence band offset controversy thus appears to have been largely resolved.