bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Al-Si Ohmic Contacts Obtained on Shallow Junctions by Laser and Electron Beam Annealing
Authors: Armigliato A. , De Luca P. , Finetti M. , Solmi S.
Published: March 2011

In this work the capability of pulsed ruby laser and multiscan electron beam techniques in the formation of Al-Si ohmic contacts on shallow (0.3 μm) junctions has been investigated. To measure the contact resistivity, properly designed test patterns have been employed, whereas to evaluate the junction leakage induced by the Al-Si interaction during sintering, the diode reverse current has been tested.

Laser beam annealing gives rise to scattered values of contact resistivity, ranging from 10-4 to 5 × 10-3 ohm-cm2 without any clear dependence on the energy used. The corresponding diode reverse currents were higher than those of the unannealed specimens by about three orders of magnitude.

E-beam annealing achieves contact resistivities on the order of 10-5 ohm-cm2 typical of conventional thermal treatment, with a parallel increase in the reverse current by only one order of magnitude.

These results indicate electron-beam annealing as a promising technique in the realization of Al-Si ohmic contacts for VLSI technology.
Beam Processing in Silicon Device Technology
Authors: Hill C.
Published: March 2011

Three modes of beam processing are distinguished, characterised by the heat pulse duration. The suitability of each of these modes as a process step in integrated circuit fabrication is discussed with reference to six criteria for applicability. Some conclusions are made as to the eventual application of each mode of processing.
Scanning E-Beam Annealing of Mos Devices
Authors: Speight J.D. , Glaccum A.E. , Machin D. , Mcmahon R.A. , Ahmed H.
Published: March 2011

Conditions for the scanning e-beam activation of P and As implanted source and drain junctions in production NMOS Si gate devices have been established. MOS devices with e-beam annealed, As-implanted, source and drain regions have been produced. The transistor parameters are found to be close to those of furnace annealed control devices, but e-beam annealed devices exbibit a smaller short-channel effect.
Phase Transitions in Amorphous SI Produced by Pulsed Laser or Electron Irradiation
Authors: Baeri P. , Foti G. , Poate J. M. , Cullis A. G.
Published: March 2011

Amorphous, implanted, Si layers have been melted by pulsed electron irradiation. Implanted As has been used as a marker for determining melt duration. Systematic differences between As diffusion in initially amorphous or crystalline Si are interpreted in terms of different enthalpies of melting between amorphous (1220 J/g) and crystalline (1790 J/g) Si. The amorphous Si layers melt and crystallize at significantly lower electron energies than those required to melt crystalline Si, indicating that amorphous Si melts at 1170K compared to 1685 K for crystalline Si. We have used these thermodynamic parameters to successfully predict some of the phenomena associated with the laser induced melting and crystallization of amorphous Si.
Formation of Sic, Si3N4 and SiO2 by High-Dose Ion Implantation and Laser Annealing
Authors: Chiang S.W. , Liu Y.S. , Reihl R.F.
Published: March 2011

High-dose ion implantation (1017 ions-cm−2) of C+, N+, and O+ at 50 KeV into silicon followed by pulsed laser annealing at 1.06 μm was studied. Formation of SiC, Si3N4, and SiO2 has been observed and investigated using Transmission Electron Microscopy (TEM) and Differential Fourier-Transform Infrared (FT-IR) Spectroscopy. Furthermore, in N+-implanted and laser-annealed silicon samples, we have observed a cell-like structure which has been identified to be spheroidal polycrystalline silicon formed by the rapid laser irradiation.
Generation of Electron Beams for Materials Processing
Authors: Fabian Pease R.
Published: March 2011

Electron beams can be used for processing materials both through thermal effects and through nonthermal, or chemical, effects. Although most interest for the last 10 years or more has been on nonthermal effects, there has recently been revived interest in electron beam heating. Such beams can be pulsed flood beams of large area (8 cm diameter), large current density (500 A cm−2) and electron energies of 5–30 keV. At the other extreme are focused cw beams of a few μm diameter and currents of about 50 μA which can be used for selective heating. There are also systems which generate ribbon beams which are effective for well controlled annealing of large areas.
Laser Annealing of the Double-Hetero Si(lll)/CoSi2/Si Structure
Authors: Ishiwara Hiroshi , Saitoh Shuichi , Mitsui Kuniaki , Furukawa Seijiro
Published: March 2011

Theoretical and experimental studies on the laser annealing of a Si/CoSi2/Si structure are presented. The power absorption in each layer in this structure is theoretically considered using the refractive index and extinction coefficient in CoSi2 and Si, which have been measured by the ellipsometric analysis. Next, an amorphous Si film deposited onto a Si(lll)/CoSi2 structure is annealed by a Q-switched ruby laser. It has been shown from Rutherford backscattering and channeling measurements that the Si film grows epitaxially onto the Si/CoSi2 structure and that an optimum power density to minimize the aligned yield in a Si film 100 nm thick exists around 1.5 J/cm2. Reflecticn electron diffraction and otpical ricroscope analyses are also used to check the crystalline quality and surface structures of the laser-annealed samples.
Post-Irradiation Annealing of Laser-Formed Silicide Layers
Authors: Wittmer M. , von Allmen M.
Published: March 2011

We have investigated the post-irradiation annealing effects of laser-formed Pt, Pd, Rh and Ni-silicides. It was found from Rutherford backscattering and x-ray analysis that compositional changes occur during subsequent high temperature annealing in a vacuum furnace. Generally, a single silicide phase tends to form at the expense of the other phases present following laser irradiation. The surviving phase is not necessarily identical to the end-phase found in a binary solid-state reaction couple of the same system.
Raman Spectroscopic Evaluation of Silicides Formed with A Scanned Electron Beam
Authors: Nemanich R. J. , Sigmon T. W. , Johnson N. M. , Moyer M. D. , Lau S. S.
Published: March 2011

Raman scattering and Rutherford backscattering are used to study the products of SEM processing of Pd and Pt thin films on Si(100) substrates. The RBS measurements indicate the compositional depth profile of the resulting silicide while the Raman scattering indicates the crystal structure. For both cases it is found that the resultant silicide is dominated by Pd2 Si (or Pt2Si) structures but evidence of deviations are also noted.
Laser Quenched Metal-Silicon Alloys
Authors: Allmen M. Von , Affolter K. , Wittmer M.
Published: March 2011

Q-Switch laser pulses are used to convert vapor-deposited metal-Si thin films into the amorphous state by a melting, mixing and quenching process. Experimental findings obtained with the metals Au, Pt, Pd, V and Nb are presented and compared with results from a numerical simulation of the laser induced melting and quenching process.
Pulsed Laser Annealing of Aluminum
Authors: Wampler W. R. , Follstaedt D. M. , Peercy P. S.
Published: March 2011

Pulsed ruby laser irradiation of unimplanted single crystal and implanted polycrystalline Al has been studied with ion beam analysis and TEM. The results show that Al is melted to a depth of ∼ 0.9 μm with a 4.2 J/cm2 , 15 nsec pulse, and that vacancies are quenched into Al during resolidification. Diffusion of Zn in liquid Al is observed, and a melt time of ∼ 65 nsec is estimated for a 3.8 J/cm2, 30 nsec pulse. The observations are in reasonable agreement with calculations of sample temperature and melt times. We observe no precipitation of AlSb in liquid Al for Sbimplanted Al, and conclude that the nucleation time satisfies 50 nsec ≲ tnuc ≲ 200 nsec. We find no evidence for amorphous Al after irradiation of single crystal Al with energies ≳ 1.5 J/cm2.
Kinetic Effects and Mechanisms Limiting Substitutional Solubility in the Formation of Supersaturated Alloys by Pulsed Laser Annealing
Authors: White C. W. , Appleton B. R. , Stritzker B. , Zeiner D. M. , Wilson S. R.
Published: March 2011

Pulsed laser annealing of silicon implanted by Group (III, V) dopants leads to the formation of supersaturated alloys by nonequilibrium processes occurring in the interfacial region during liquid phase epitaxial regrowth. The distribution coefficient from the melt (k') and the maximum dopant substitutional solubility (CSmax) are far greater than equilibrium values and both are functions of growth velocity. Substitutional solubility is limited by lattice strain and by constitutional supercooling at the interface during regrowth. Values for CSmax obtained at different growth velocities are compared with predictions of thermodynamic limits for solute trapping.
Laser Pulse Melting of Metals: Epitaxy and Allotropy
Authors: Buene L. , Kaufmann E. N. , Preece C. M. , Draper C. W.
Published: March 2011

Laser pulse melted single crystals of several metals have been examined by the Rutherford backscattering/channeling technique and with optical and scanning electron microscopy. Metals belonging to the three major structure groups; fcc (Ni, Pd, Rh); bcc(Mo, Nb, W, Fe); and hcp (Be, Ti, Re) have been studied at various laser power levels and in different crystallographic orientations. Of these cases, Be, Ti and Fe show high temperature allotropes which are expected to influence the character of the resolidified surface layer.
Laser Induced Defects and Materials Interactions in the V-Si System
Authors: Appleton B. R. , Stritzker B. , White C. W. , Narayan J. , Fletcher J. , Meyer O. , Lau S. S.
Published: March 2011

Pulsed laser annealing has been evaluated as a technique for fabricating superconducting V3 Si from multilayer V-Si samples, and the nature of laser-induced defects in V3 Si single crystals has been examined. Correlated analyses by ion scattering, ion channeling, Tc measurements and TEM were used to examine the composition and structure of samples subjected to single and multiple laser pulses. It was observed that although the superconducting A15 phase could be formed by pulsed laser mixing, the associated rapid quenching effects introduced defects which were not completely removed by thermal annealing to 925 K for 1 hour. Ion channeling and TEM studies of V3 Si single crystals showed that pulsed laser irradiation caused microcracks to develop in the surface, probably from mechanical stresses induced by thermal gradients.
High Power Laser Effects on Unimplanted and Implanted Aluminium Single Crystals
Authors: Battaglin G. , Carnera A. , Mea G. Della , Mazzoldi P. , Jain A.K. , Kulkarni V.N. , Sood D.K.
Published: March 2011

Mechanisms involved in laser processing of ion implanted semiconductors have been extensively investigated (1,2). Relatively little work has been done on implanted metals (3,10). The liquid solid interface (melt front) velocity in metals (11,12) is much larger than that in Si. Therefore several nonequilibrium effects on recrystallization (6) solute segregation (9) and metastable phase formation (4,6,7) are observed. Such effects would depend on the melt front velocity, equilibrium phase diagram considerations (such as equilibrium segregation coefficient Ko, miscibility in licuid phase, intermediate phases etc.) and also on the as implanted nonequilibrium phase and defect structure. In this paper we present a study of the influence of some of these parameters during laser treatment of sincle crystals of virgin Al and dilute implanted alloys of Mo and Cd in Al.
Convection in Pulsed Laser Formed Melts
Authors: Possin G. E. , Parks H. G. , Chiang S. W.
Published: March 2011

In 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

Two 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

Laser 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

Sputtered 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

A 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

ZnSe: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

We 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

The 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

This 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

The 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

A 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

Hg1−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

A 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

The 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

Anodic 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

A 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

Synchrotron 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

Single 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

Growth 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

A 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

The 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

The 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

HgTe: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

We 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

Results 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

The 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.
HgTe-CdTe Multiple Quantum Wells
Authors: Hoffman C. A. , Arnold D. J. , Meyer J. R. , Bartoli F. J. , Lansari Y. , Cook J. W. , Schetzina J. F. , Schulman J. N.
Published: March 2011

We report a detailed magneto-transport investigation of HgTe-CdTe multiple quantum wells. The data yield the first experimental confirmation of a theoretically-predicted “negative-gap” semiconducting region in wide-well Hg-based heterostructures. Gaps of up to 19 meV are observed.
Quantum-Confined Stark Effect in II-VI Semiconductor Coupled Quantum Wells
Authors: Yang Z. , Schetzina J. F.
Published: March 2011

The Quantum-Confined Stark Effect in II-VI semiconductor coupled quantum wells is studied theoretically. It is found that because of the difference in localization of the wavefunctions of the heavy hole and the electron subbands involved, large band gap shifts can be induced by an external electric field for quantum wells with zero-field band gaps in the spectrum region from 0.4 µm to 12 µm. Several potential device applications based on this effect are proposed.
Energy Level Spectra of Transition Metal Ions In Diluted Magnetic Semiconductors
Authors: Villeret Murielle , Rodriguez S. , Kartheuser E.
Published: March 2011

We present a study of the low lying energy levels of Fe2+, Co2+, Ni2+ and Cu2+ in diluted magnetic semiconductors such as Cd1−xCoxTe and Cd1−xCoxSe and their counterparts. In the first of these compounds the magnetic ion sits on a site of symmetry Td while in the second the symmetry is trigonal (C3v). We develop a formulation that permits a continuous variation from Td to C3v symmetry. Comparison with experimental data in Cd1−xCoxSe shows that the C3v distortion amounts to about 10% of the crystal potential at the Co2+ site. Our study of the energy spectra of Fe2+ in Td and C3v crystal potentials reveals that, even in the cubic field, the levels exhibit an anisotropy which manifests it- self in an anisotropy of the magnetization, , in the regime in which is not a linear function of the magnetic field . The study includes all the levels in the lowest terms of the (3d)n (n=6,7,8,9) configurations. The calculations are carried out to second order in the spin-orbit interaction and in for the lowest orbital states and to first order in for the excited states. The g-factors of all the levels are obtained including their anisotropy for the Co2+ and Cu2+Γ8states.
Raman Spectroscopy of A Novel Diluted Magnetic Semiconductor: Cubic Cd1−xMnxSe.
Authors: Alonso R. G. , Suh E.-K. , Pascher H. , Oh E. , Ramdas A. K. , Samarth N. , Luo H. , Furdyna J. K.
Published: March 2011

In contrast to the bulk diluted magnetic semiconductor (DMS) Cd1−xMnxSe which occurs with the wurtzite structure, its epilayers grown on (001) GaAs substrate by Molecular Beam Epitaxy exhibit the cubic zinc-blende structure. Raman spectroscopy and photoluminescence studies on this novel DMS show (1) a “two-mode” behavior of the zone center optical phonons, (2) the Raman line associated with the spin-flip in the Zeeman split S = 5/2 ground state of Mn2+, and (3) large Raman shifts associated with the spin-flip of donor-bound electrons. The large magnetic field dependence in (3) with saturation at high fields and low temperature shows that the s-d exchange interaction characteristic of DMS's is also manifested strikingly in the zinc-blende phase of Cd1−xMnxSe.
Free Exciton Magnetospectroscopy of CdFeSe Diluted Magnetic Semiconductor
Authors: A Twardowski , K Pakula , M Arciszewska , A Mycielski
Published: March 2011

The magnetospectroscopy data of free exciton in hexagonal Cd1−xFexSe are presented for different magnetic field orientation. Combining exciton splitting data with magnetic susceptibility data we estimate p-d exchange integral for CdFeSe valence band.
High Resolution and Analytical Electron Microscopy of Multilayer Heteroepitaxial Semiconductors
Authors: Kleebe H.-J. , Hamilton W.J. , Ahlgren W.L. , Johnson S.M. , Rühle M.
Published: March 2011

Thin-film epitaxial layers on silicon substrates are being actively developed as an alternative to bulk substrates for infrared detectors. Success in this development is expected to yield improvements in size, strength, monolithic signal processing, and cost of the detector arrays. To provide feedback to the thin-film growth process, this study has investigated the structural and chemical properties of these films. CdTe or CdZnTe was grown on GaAs on Si wafers by metalorganic chemical vapor deposition (MOCVD) followed by the growth of HgCdTe by liquid-phase epitaxy (LPE). Development of TEM specimen preparation techniques permitted investigation of materials with up to four layers. Cross sectional TEM and AEM investigations resulted in the following observations: Selected area diffraction and CTEM show relations between the layers and structural defects. High resolution imaging of the multilayers reveals that most of the heteroepitaxial misfit is accomodated by misfit dislocations. Many, but not all, stacking faults and dislocations which propagate across the films appear to be related to structural interface defects. The evidence indicates that there is little, if any, contamination at MOCVD and LPE interfaces. Interface defects mainly appear to be extremely minute pits or hillocks. AEM investigations of interface regions have demonstrated a redistribution of material close to the CdZnTe / HgCdTe interface.
Thickness Measurement of Thin Films by X-Ray Absorption
Authors: Chaudhuri J. , Shah S.
Published: March 2011

An x-ray diffraction method is described for determining thicknesses of thin films grown on single crystal substrates. The equations, based on the kinematical theory of x-ray diffraction and the mosaic crystal model, were developed. The thickness of the thin film was computed from the absorption of the integrated diffracted x-ray intensity from the single crystal substrate by the film. Since the diffracted intensity from the film is not required, the film does not have to be single crystal in nature. Thus, thicknesses of less ordered, polycrystalline or even amorphous films can be measured with high precision by this technique.
MOCVD Growth and Doping of ZnSe and Related II-VI Materials
Authors: Kukimoto Hiroshi
Published: March 2011

Recent progress in metalorganic chemical vapor deposition (MOCVD) of wide bandgap II-VI materials, especially of ZnSe, ZnS and their alloys, is discussed with emphasis on the general principles for obtaining uniform and high quality epitaxial layers and the current major issue of impurity doping for achieving conductivity control. The surface morphology and crystalline quality can be improved by a suitable choice of source materials and by lattice-matching the epitaxial layer to the substrate. By using appropriate sources, high conductivity n-type epitaxial layers of ZnSe and ZnS doped with impurities from group HI and VII of the periodic table have been successfully grown by low temperature MOCVD. We have also grown p-type ZnSe layers with carrier concentration ranging from low 1016 to high 1017 cm−3 using Li3N as the dopant. Extensive studies are now focussed on the better p-type control. High purity source materials, appropriate p-type dopants and low temperature growth are important keys.
Growth and Doping of Zinc Selenide by Molecular Bean Epitaxy
Authors: Depuydt J.M. , Cheng H. , Haase M.A. , Potts J.E.
Published: March 2011

Recently, with the advent of thermal nonequilibrium growth techniques like molecular beam epitaxy and metalorganic chemical vapor deposition, great progress has been made in overcoming some of the problems traditionally encountered in the growth and doping of ZnSe. Breakthroughs have been made in several areas including the growth of high quality undoped films, in intentional n-type doping and, most importantly, in p-type doping. In this paper we will review the progress made in the growth and doping of ZnSe by molecular beam epitaxy.
A Ten Study of an Adhesive / Sheet Molding Compound Interface
Authors: Kamenetzky Eduardo A. , Farinato Raymond S.
Published: March 2011

The interface between an epoxy adhesive and sheet molding compound (SMC) was studied by TEM. The interface width is less than 20 nm where it is sharp, and on the order of 40 nm where it is more diffuse. The interfacial area in the TEM sample is located first by the difference between adhesive and SMC microstructures. Where there are no microstructural features we can investigate further the location of the interface by using the Mg Kx peak from magnesia thickener in the polyester matrix of the SMC. Calcium carbonate crystals in the SMC extend to within less than 25 nm of the interface. Measurements of interface extent and roughness indicate that there is intimate contact and good mechanical bonding between the adhesive and SMC. The surface and interfacial energetics of this epoxy-SMC system were evaluated using sessile drop advancing contact angles. Good mechanical bonding observed by TEM is consistent with a small advancing contact angle of 20°the epoxy adhesive on the SMC at 121 °C which shows a good thermodynamic driving force for the intimate contact during the bonding process.
The Influence of Water on the Epoxy-Resin-Glass Interphases
Authors: Marzi T. , Schröder U. , Heß M. , Kosfeld R.
Published: March 2011

abstract

The absorption of water in glass fiber reinforced epoxy resins is a complex process. With dynamic-mechanical measurements it is possible to distinguish locations of water in the resin-glass interphase, in micro-cracks of the resin, and diluted in the bulk polymer. The dominant mechanism of incorporation depends on the resin/hardener system, the surface treatment of the glass fabrics, and the sorption temperature.
ACID/BASE Interactions with Silicon Carbide Fiber
Authors: Wesson Sheldon P. , Allred Ronald E.
Published: March 2011

Silicon carbide fiber surfaces were analyzed by programmed thermal desorption and inverse gas chromatography, using Lewis acids and bases as probe adsorbates to compare the effect of RF glow discharge plasma and thermal treatment on surface energetics. Changes in surface acid/base character were correlated with wetting data, surface titrations, and surface chemical composition deduced from x-ray photoelectron spectroscopy. Thermal treatment did not alter fiber surface energetics significantly. Plasma treatment rendered the surface more acidic and more basic. XPS and thermal desorption analysis indicate that the plasma removed: strongly adsorbed organic contaminants, exposing and activating the underlying glassy surface.
Interfacial Reactions of Refractory Metals Niobium and Tantalum with Ceramics Silicon Carbide and Alumina
Authors: Joshl A. , Hu H. S. , Wadsworth J.
Published: March 2011

Recent interest in the development of advanced metal matrix composites has prompted research on interfacial reactions of Nb and Ta with candidate reinforcements such as silicon carbide and alumina. Formation of reaction layers as small as 0.1 μm can be detrimental to composite strength and ductility and in some instances to the corrosion behavior, which suggests the importance of understanding the early stages of interfacial reactions. Thin films of Nb and Ta were sputter deposited on single crystal and polycrystalline silicon carbide and on sapphire substrates, and the nature and extent of reaction evahiated using Auger depth profiling and electron microscopy. In the Nb/SiC system, NbCX is the first reaction product to form, but the overall extent of the reaction is dominated by the formation of the more stable NbCXSiY ternary phase. Little or no interfacial reaction was observed in the Nb/Al2O3 system for up to 4 hburs at 1100°C, which also suggests that Al2O3 may be a potential diffusion barrier to minimize reactions in the Nb/SiC system. Similar interesting observations were made in the Ta/SiC and Ta/Al2O3 systems.
Chemical Interactions in the Aluminum-Carbon and Aluminum-Silicon Carbide Systems
Authors: Maruyama Benji , Ohuchi Fumio S. , Rabenberg L.
Published: March 2011

X-ray Photoelectron Spectroscopy (XPS) was used to investigate the influence of O2 and H2O on the formation of aluminum carbide at aluminum-carbon and aluminumsilicon carbide interfaces. It was determined that dosing the interfaces with H2O catalyzed the formation of aluminum carbide in both the aluminum-carbon and aluminum-silicon carbide systems. This result is consistent with the oxidation model of carbide formation [1], previously developed to understand the kinetics of aluminum carbide formation at graphite-aluminum interfaces. These results imply that the formation of aluminum carbide in graphite and silicon carbide reinforced metal matrix composites, which severely degrades the composite mechanical properties by degrading the fiber and interface strength [2], is catalyzed.