bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth and Characterization of CDTE and CDTE Alloys
Authors: Mcdevitt S. , John D.R. , Sepich J.L. , Bowers K.A. , Schetzina J.F. , Rai R.S. , Mahajan S. 
Published: March 2011

ABSTRACTMethods used to grow bulk, CdTe crystals, effects of alloying on their perfection and typical single crystal properties are reviewed in this paper. Crystals grown by a modified horizontal Bridgman technique have lower dislocation densities than those grown by a modified vertical Bridgman method. Dislocation densities of the order of 1×103/cm2 have been observed in CdTeSe crystals grown by the former technique. Due to the difference in the distribution coefficients of Zn and Se in CdTe, CdTeSe ingots are chemically more uniform than CdZnTe ingots. Purity studies of starting materials indicate that Se substitutions may introduce more impurities than Zn additions.
Growth of ZnSxSe1−x by Mbe Using An Electrochemical Sulphur Source.
Authors: Wallace J.M. , Prior K.A. , Caveneif B.C. , Hunter J.J. , Adams S.J.A. , Haines M.J.L.S. 
Published: March 2011

ABSTRACTIn this paper we describe the use of an electrochemical sulphur cell to grow ZnSxSe1−x alloys on GaAs substrates. The cell uses the ionic transport of Ag ions in Ag2S to produce a sulphur flux which depends on the applied voltage. The advantages and disadvantages of this type of source will be discussed. We also describe the versatility of the cell for fabricating ZnSxSe1−x/ZnSySe1−y multilayers as well as more complex profiles.
Selective Area Deposition of Passivants, Insulators, and Epitaxial Films of II-VI Compound Semiconductors
Authors: Dreifus D.L. , Lansari Y. , Han J.W. , Hwang S. , Cook J.W. , Schetzina J.F. 
Published: March 2011

ABSTRACTII-VI semiconductor surface passivants, insulators, and epitaxial films have been deposited onto selective surface areas by employing a new masking and lift-off technique. The II-VI layers were grown by either conventional or photoassisted molecular beam epitaxy (MBE). CdTe has been selectively deposited onto HgCdTe epitaxial layers as a surface passivant. Selective-area deposition of ZnS has been used in metal-insulator-semiconductor (MIS) structures. Low resistance ohmic contacts to p-type CdTe:As have also been realized through the use of selectively-placed thin films of the semi-metal HgTe followed by a thermal evaporation of In. Epitaxial layers of HgTe, HgCdTe, and HgTe-CdTe superlattices have also been grown in selective areas on CdZnTe substrates, exhibiting specular morphologies and double-crystal x-ray diffraction rocking curves (DCXD) with full widths at half maximum (FWHMs) as narrow as 140 arcseconds.
Atomic Layer Epitaxy of Wide Bandgap II-VI Compound Semiconductor Superlattices
Authors: Konagai M. , Takemura Y. , Kimura R. , Teraguchi N. , Takahashl K. 
Published: March 2011

ABSTRACTZnSe, ZnTe and ZnSe-ZnTe strained-layer superlattices (SLS's) have been successfully grown by atomic layer epitaxy (ALE) using molecular beam epitaxy (MBE-ALE). The ideal ALE growth, i.e., one monolayer per cycle of opening and closing the shutters of the constituent elements, was obtained for ZnSe in the substrate temperature range of 250-350° C. However, for ZnTe, precise control of the Te beam intensity is needed to obtain the ALE growth. Optical properties of the (ZnSe)l-(ZnTe) 1 SLS were evaluated by photoluminesence. ZnSe films were also grown by ALE using metalorganic molecular beam epitaxy (MOMBE-ALE). Diethylzinc (DEZn), diethylsulfur (DES) and diethylselenium (DESe) were used as source gases for Zn, S and Se, respectively. The ALE growth of ZnSe was achieved at substrate temperature between 250 and 300° C which is about 150° C lower than that for the conventional MOMBE.
Excitonic Properties of ZnSe-ZnS Strained-Layer Superlattices and A Fibonacci Sequence
Authors: Taguchi Tsunemasa , Yamada Yoichi 
Published: March 2011

ABSTRACTExcitonic properties of ZnSe-ZnS strained-layer quantum wells (SLQWs) with type I band lineups are reviewed on the basis of our recent results of temperature- and strain-dependent photoluminescence and absorption spectra. In order to estimate the conduction and valence band offsets as a function of ZnSe well thickness, we have modified the “model-solid” theory in which the valence bands (heavy-hole band in ZnSe and light-hole band in ZnS) are relatively moved with strains. Temperature and high excitation dependent studies of the n=1 heavy-hole excitons suggest a localization of excitons and reveals the important evidence on scatterings of excitons with acoustic and optical phonons. The thermal quenching of the exciton emission is caused by thermal dissociation of quasi-two-dimensional excitons through electrons and holes, from which the activation energy for this dissociation is 4 times larger than Ea.3D (a binding energy of bulk exciton) of ZnSe. A new superlattice structure with a quasiperiodic crystal which is derived from a finite Fibonacci sequence, has been fabricated by a low-pressure MOCVD method and its photoluminescence properties are for the first time introduced.
Photoassisted MBE of II-VI Semiconductor Films and Superlattices
Authors: Giles N.C. , Harper R.L. , Han J.W. , Schetzina J.F. 
Published: March 2011

ABSTRACTThis paper will review recent progress in the growth of II-VI semiconductors at NCSU by photoassisted molecular beam epitaxy, an energy-assisted growth technique in which the substrate is illuminated during the entire growth process. The materials focused on here include undoped and As-doped CdTe, As-doped HgCdTe, and In-doped HgCdTe. These materials were grown as single epilayers, as well as incorporated in other structures including heterojunctions and modulation-doped superlattices. The photo-assist during growth has allowed a substantial reduction in substrate growth temperatures, as well as an enhanced activation of n-type and p-type dopant species. The structural, electrical, and optical properties of the samples will be discussed below.
First and Second Order Raman Studies of Composition and Structural Ordering in Hg1−xCdxTe
Authors: Compaan A. , Bowman R. C. 
Published: March 2011

ABSTRACTThe effects of alloy fluctuations, defect densities, and short-range clustering on the resonance behavior of first and second order LO and TO Raman scattering are studied in Hg1−xCdxTe (MCT). X-values between 0.20 and 0.32 and photon energies from 2.35 to 2.7 eV were used with samples prepared by a wide range of techniques--LPE, MOCVD, MBE, bulk growth, and pulsed laser annealing. We examine the resonance behavior of the HgTe-like TO mode at ∼120 cm−1 and the mode at 133 cm−1, which has been identified as originating from the preferential clustering of 3 Hg and 1 Cd about the Te. We find that the intensity of this peak for various bulk and epitaxially grown samples is unusually large only near the E, resonance. Pulsed laser annealing with a Nd:YAG-pumped dye laser strongly suppresses this mode in all samples suggesting that extremely rapid epitaxial regrowth may inhibit the 3:1 cluster formation. In addition, the resonance-enhanced LO overtones are suppressed by the pulsed laser anneal.
Temperature-Dependent Infrared Absorption of Hg-Based II-VI Semiconductor Superlattices
Authors: Yang Z. , Lansari Y. , Han J. W. , Yu Z. , Schetzina J. F. 
Published: March 2011

ABSTRACTThe optical absorption of a series of HgTe/Cd0.85 Hg0. 15 Te superlattices (SLs) have been measured in the spectral region from 2 to 12 µm at temperatures from 300 K down to 4.2 K. Several subband transitions were identified and their transition energies were compared with theoretical calculations, with the valence band offset δEv between HgTe and CdTe as a fitting parameter. It is found that at a given temperature, a value of δEv = 420 ± 100 meV fits the results of all the SLs, and δEv does not depend on temperature to within ±100 meV.
Properties of Modulation-Doped HgCdTe Superlattices
Authors: Hwang S. , Yang Z. , Lansari Y. , Han J.W. , Cook J.W. , Giles N.C. , Schetzina J.F. 
Published: March 2011

ABSTRACTPhotoassisted molecular beam epitaxy has been employed to successfully prepare p-type and n-type modulation-doped HgCdTe superlattices. The samples were grown at 170°C. In this paper, we report details of the MBE growth experiments and describe the optical and electrical properties that these new multilayered quantum well structures of HgCdTe possess.
Electrical Characterisation of P-Type CdxHg1−xTe Grown by Movpe
Authors: Royle Anne , Gough J S , Irvine S J C , Mullin J B 
Published: March 2011

ABSTRACTThe results of electrical characterisation of a series of MOVPE layers of CdxHg1−xTe (CMT) grown by the interdiffused multilayer process (IMP) are reported. It is shown that the properties of the CMT layers when grown as a “sandwich” between CdTe buffer and cap layers display classical p-type Hall effect curves. These have been modelled and the sensitivity of the fitting parameters are reported. It is shown that there is evidence of complex (“anomalous”) two-layer like behaviour in low x material which is not attributable to inversion behaviour.
Low Temperature Device Processing Technology for II-VI Semiconductors
Authors: Dreifus D.L. , Kolbas R.M. , Sneed B.P. , Schetzina J.F. 
Published: March 2011

ABSTRACTLow temperature (<60° C) processing technologies that avoid potentially damaging processing steps have been developed for devices fabricated from II-VI semiconductor epitaxial layers grown by photoassisted molecular beam epitaxy (MBE). These low temperature technologies include: 1) photolithography (1 µm geometries), 2) calibrated etchants (rates as low as 30 Å/s), 3) a metallization lift-off process employing a photoresist profiler, 4) an interlevel metal dielectric, and 5) an insulator technology for metal-insulator-semiconductor (MIS) structures. A number of first demonstration devices including field-effect transistors and p-n junctions have been fabricated from II-VI epitaxial layers grown by photoassisted MBE and processed using the technology described here. In this paper, two advanced device structures, processed at <60° C, will be presented: 1) CdTe:As-CdTe:In p-n junction detectors, grown in situ by photoassisted MBE, and 2) HgCdTe-HgTe-CdZnTe quantum-well modulation-doped field-effect transistors (MODFETs).
Free-Carrier Induced Optical Nonlinearities in Narrow Bandgap Semiconductors
Authors: Walrod D. , Auyang S. Y. , Wolff P. A. 
Published: March 2011

ABSTRACTFree-carrier induced third-order optical nonlinearities can be both large and fast in narrow-gap semiconductors. We have studied a variety of mechanisms in bulk semiconductors and heterostructures using CO2 lasers and found third-order susceptibilities as large as 2×10−3 esu with picosecond relaxation times. These mechanisms saturate at much higher intensities than do slower mechanisms and hence induce huge modulations of the dielectric function. In addition, most of these processes are nonresonant so they do not require the exact matching of material parameters and are relatively insensitive to temperature.
Narrow-Gap Nonlinear Optical Materials
Authors: Youngdale E. R. , Hoffman C. A. , Meyer J. R. , Bartoli F. J. , Han J. W. , Cook J. W. , Schetzina J. F. , Martinez A. 
Published: March 2011

ABSTRACTWe report an experimental study of the nonlinear optical properties of HgTe-CdTe superlattices grown by MBE and Pb1−x,SnxSe grown by hot wall epitaxy. Nondegenerate four-wave mixing has been employed to measure third-order nonlinear susceptibilities at 10.6 µm as a function of temperature, laser intensity, and difference frequency. The nonlinearity is believed to be due to modulation of the free carrier temperature and density by the optical beams. The HgTe-CdTe results are compared to theoretical calculations based on free carrier contributions to the susceptibility, and the agreement with experiment is quite good. In 1-µm-thick Pb1−xSnxSe layers, multiple internal reflections of the light within the sample is found to enhance the nonlinear signal by an order of magnitude.
Recent Developments in II-VI Diluted Magnetic Semiconductors
Authors: Samarth N. , Furdyna J. K. 
Published: March 2011

ABSTRACTMuch of the work in diluted magnetic semiconductors (DMS) in past years has focused on the alloys such as Cd1−xMnxTe. Recently, there has been an increasing accent on DMS alloys containing the transition metal ions Fe2+ and Co2+. We review here the properties of these new materials and compare them with the alloys. We also examine the novel opportunities afforded by the molecular beam epitaxy of epilayers and heterostructures containing the “metastable” zinc-blende phase of Cd1−xMnxSe.
Photoluminescence Studies of Diluted Magnetic Semiconductors Under Hydrostatic Pressure: Cd1−xMnxTe
Authors: Prakash Maneesha , Chandrasekhar Meera , Chandrasekhar H.R. , Miotkowski I. , Ramdas A.K. 
Published: March 2011

ABSTRACTWe present a photoluminescence study of the excitons and electron-to-acceptor (e-°) transitions in Cd1−xMnxTe (x = 0.05 and 0.15) under hydrostatic pressure at 15K. We investigate the changing magnetic and Coulombic binding energies of the e-° transition under pressure. We find that the e-° binding energy increases with pressure for x = 0.15 where the magnetic term due to the acceptor bound magnetic polaron is large, while it decreases for x = 0.05. We also obtain the pressure coefficients of the excitonic and acceptor related transitions.
In-Situ Studies of Semimagnetic Heterojunction Parameters
Authors: Yu Xiaohua , Troullier N. , Raisanen A. , Haugstad G. , Franciosi A. 
Published: March 2011

ABSTRACTWe have conducted a systematic study of Ge-Cd1−xMnxTe heterostructures prepared in situ by deposition of polycrystalline Ge onto atomically clean Cd1−xMnx (110) surfaces. We examined by means of high resolution synchrotron radiation photoemission the valence band offset δEv as a function of the substrate composition x (x=0, 0.35, and 0.60) and bandgap Eg (Eg = 1.47, 1.93, and 2.13 eV). We find δEv=0.84±0.10eV in all cases, and no dependence of δEv on the substrate bandgap within experimental uncertainty. This finding indicates that within the range of validity of the transitivity rule, Cd1−xMnx-Cd1−yMny heterojunctions may actually follow the common anion rule.
Pulsed Laser Evaporation and Epitaxy Growth of Cd1−xMnxTe
Authors: Zheng X.L. , Huber C.A. , Becla P. , Shih M. , Heiman D. 
Published: March 2011

ABSTRACTEpitaxial layers of Cd1−xMnxTe have been grown on CdTe (100) substrates by evaporating a target with a 1.06 µm pulsed laser. The high - quality materials were characterized by photoluminescence spectroscopy (PL) and energy dispersive analysis of x-ray (EDAX). We find that the incorporation of the Mn in the epitaxial layer is about two - thirds of the concentration in the target. A comparison is made to the epitaxial layers grown on CdTe (111) and GaAs (100) substrates.
Photoluminescence of ZnSe Epilayers on GaAs Under Hydrostatic Pressure
Authors: Tuchman Judah A. , Sui Zhifeng , Herman Irving P. , Gunshor R. L. , Kolodziejski L. A. , Cammack D. A. , Shone M. 
Published: March 2011

ABSTRACTThe near bandgap photoluminescence of ZnSe epilayers grown on GaAs substrates is measured for pressures up to ∼25 kbar using a diamond anvil cell at T = 9 K. The bandgap changes with pressure, dE/dp, for pseudomorphic and nonpseudomorphic films are obtained, and are compared with results for bulk crystalline ZnSe.
Preparation and Characterisation of (ZnTe)x(CdSe)1−x Single Crystals
Authors: Rani V.K. Madhu Smitha , Vijayalakshmi R.P. , Reddy D. Raja , Reddy B.K. 
Published: March 2011

ABSTRACTThe titlematerial is one of the least studied among the II-VI alloy systems. So far it has not been possible to prepare ZnTe in n-type and CdSe in p-type with appreciable conductivities. Moreover ZnTe crystallises in zincblende whereas CdSe crystallises in wurtzite structure. Because of the varied nature of the end compounds, an attempt has been made to prepare single crystals of (ZnTe)x(CdSe)1−x in the entire range of ‘x’. The alloy material in the entire range Xof composition in the single crystalline form was grown by a modified Piper-Plich method. The grown crystals of this alloy system have been subjected to chemical analysis. DTA and DTG studies carried out on these alloys did not show any phasec transitions. However two exothermic peaks associated with increase in mass were noticed. This has been attributed to oxidation effects of Se/Te or Cd/Zn. XRD data though showed some regularity near end compositions there is still some ambiguity for the middle compositions. Energy gap obtained from reflection spectra and also photocurrent spectral response showed bowing. However, there is a marked different feature at one of the end regions. The growth and the results of all the above mentioned investigations are presented and discussed in this paper.
Deep Level Luminescence Measurements of MBE CdTe Growth Quality and Processing
Authors: Shaw J. L. , Brillson L. J. , Sivananthan S. , Faurie J. P. 
Published: March 2011

ABSTRACTWe used photoluminescence spectroscopy to monitor CdTe in-situ during surface processing in order to optimize the surface electronic quality. Spectra of optimally-prepared (100) films grown by molecular beam epitaxy reveal low intensity emission from deep states relative to typical bulk-grown material.
Solubility of Impurities and Defect Impurity Interaction In II-VI Semiconductors
Authors: Marfaing Y. 
Published: March 2011

ABSTRACTA description of incorporation and solubility limit of substitutional impurities is made using the alloy CdxHgloxTe as a model of analysis and a source of experimental data.Then non-equilibrium incorporation of impurities under light excitation is considered. A model of photo assisted doping is presented which accounts for the high doping efficiency reported for the donor indium in photoassisted grown CdTe.
Study of Transcrystallization in Polymer Composites
Authors: Hsiao Benjamin S. , Eric J. H. 
Published: March 2011

AbstractTranscrystallization of semicrystalline polymers, such as PEEK, PEKK and PPS, in high performance composites has been investigated. It is found that PPDT aramid fiber and pitch-based carbon fiber induce a transcrystalline interphase in all three polymers, whereas in PAN-based carbon fiber and glass fiber systems, transcrystallization occurs only under specific circumstances. Epitaxy is used to explain the surface-induced transcrystalline interphase in the first case. In the latter case, transcrystallization is probably not due to epitaxy, but may be attributed to the thermal conductivity mismatch. Plasma treatment on the fiber surface showed a negligible effect on inducing transcrystallization, implying that surface-free energy was not important. A microdebonding test was adopted to evaluate the interfacial strength between the fiber and matrix. Our preliminary results did not reveal any effect on the fiber/matrix interfacial strength of transcrystallinity.
Effect of Ambient Atmosphere on Thin Film Reaction of Si3N4 with Ti
Authors: Desu Seshu B. , Taylor J. Ashley 
Published: March 2011

AbstractThe reaction of sputtered deposited Ti films of 100 nm thick with low pressure chemical vapor deposited Si3N4 films (300 nm thick) was studied in N2 or Ar, in a rapid thermal annealer. Reactions are followed using x-ray diffraction, Auger electron spectroscopy, and transmission electron microscopy. In argon, the Si3N4 and Ti reaction at low temperatures led to the product formation of two layer structure (TiN/Ti5Si3), with some contaminant oxygen and nitrogen released from the reaction uniformly dissolved throughout the remaining unreacted Ti. At higher temperatures, a three layer structure, TiN/TixSiy/TiN, on unreacted Si3N4 was developed. With increasing temperature the value of x and y decreased from 5 to 0 and 3 to 1, respectively. Reactions in N2 ambient, irrespective of temperature, always produced the three layer structure, but the thickness of TixSiy layer was much smaller than that produced in argon ambient for the corresponding temperatures. The reaction mechanism can be explained in terms of relative diffusion coefficients and the stability of the interfaces.
Stability and Reactions at Composite Interfaces of Titanium Aluminides with Potential Fiber Materials
Authors: Dekock J. A. , Chang Y. A. , Zhang M.-X. , Chen O. Y. 
Published: March 2011

AbstractThe Ti-Al-O and Ti-Al-B phase diagrams at 1100°C were estimated using thermodynamic data available in the literature assuming no ternary phases in either of the systems. Diffusion experiments consisting of a matrix of titanium aluminide with 2 at% Ta m contact with both Al2O3 and TiB2 were carded out at 1100° C for up to 192 hours.
The Effect of Temperature on the Chemistry and Morphology of the Interphase in an SCS6/Ti-6AI-4V Metal Matrix composite.
Authors: Jonesa C. , Kielya C. J. , Wang S. S. 
Published: March 2011

AbstractThe changes in chemistry and morphology within the interphase region of an SCS6/Ti-6A1-4V metal matrix composite upon exposure to varying heat treatments have been studied. It is thought that changes such as the formation of small TiC particles at one interface, and the narrowing of a protective pyrocarbon layer at another, induce fracture to occur at different places within the interphase upon heating. Evidence for a phase change on heat treatment of a TixSiy(C) layer to the more thermodynamically stable silicide phase,Ti5 Si3, is also presented.
The Effect of Fiber Coatings on Interfacial Shear Strength and the Mechanical Behavior of Ceramic Composites
Authors: Lowden Richard A. , More Karren L. 
Published: March 2011

AbstractThin coatings deposited on ceramic fibers prior to densification employing chemical vapor infiltration techniques have been used to limit fiber-matrix bonding. This has resulted in improvements in strength and toughness at room and elevated temperatures in Nicalon® fiber-reinforced/SiC matrix composites. The properties of the fiber-matrix interface in fiber-reinforced ceramic composites have been examined utilizing an indentation method in which a standard microhardness indentor is used to push on fibers embedded in the ceramic matrix. Compositions and microstructures at the interface have been characterized employing analytical electton microscopy. Correlations between interfacial phenomena and observed mechanical behavior have been made.
Tailored Interphases in Fibre Reinforced Polymers
Authors: Piggott Michael R. 
Published: March 2011

AbstractThe use of fibre coatings to enhance adhesion between fibres and polymers normally means that, in the fibre composite, some residue of the coating is present at the fibre-matrix interface. This constitutes the interphase. The mechanical properties of this material may be measured using simple fibre pull out tests. These tests have the advantage of revealing the interphase failure mode (i.e. brittle or ductile) as well as providing such data as work of fracture, yield stress, interfacial pressure and the coefficient of friction for post-debonding slip. Results obtained so far indicate some ductility and yielding with thermoplastic interphases, although final failure is brittle. Thermoset interphases appear to be universally brittle, with small works of fracture (10-200 Jm−2 ). The change in Young's modulus across the interphase may be a factor influencing brittle fracture, the biggest change giving the most brittle interphase.The ideal interphase should probably have a modulus intermediate between that of the fibre and the polymer, together with moderate yield stress, to give the composites adequate shear strength and good impact resistance through promotion of fibre pull outs.