bluuebunny/crossref_metadata_2025 huggingface dataset:
Benchmark of Surface Mount Autoclave Reliability Performance
Authors: Savage Timothy Scott , Masteller Melissa , Burkhard Dave , Lau S. C.
Published: March 2011

This benchmark study examined the effect of four different backmetal/ leadframe schemes on the time to failure from autoclave testing for surface mount, small signal transistors in the SC59 package configuration. The four schemes examined included die with Au backmetal bonded to a Cu plated Alloy 42 leadframe, Au backmetal bonded to a Ag striped, Ni plated, Cu plated alloy 42 leadframe, Au backmetal with a thin, permeable Ni layer bonded to a Ag striped, Ni plated Cu leadframe and V/Ni/AuGe/Au backmetal bonded to a Cu leadframe. Devices with AuSi eutectic bonded directly to the Cu plated Alloy 42 leadframe separated between the Si die and the AuSi eutectic after 240 hours of autoclave testing which produced VCESAT failures. Identical devices bonded to Ag striped, Ni plated, Cu plated Alloy 42 leadframes had the same failure mechanism after 624 hours of autoclave testing. Adding a permeable Ni layer to the AuSi eutectic structure and bonding to a Ag striped, Ni plated Cu leadframe increased the lifetime to 744 hours but still produced the same failure mechanism. Devices using a V/Ni/AuGeJAu bonded to a Cu leadframe remained electrically good and physically intact after 864 hours of autoclave testing. These results indicate the use of leadframe plating and/or backmetal barrier metals is needed in order to produce devices that can withstand extended reliability testing.
Noninvasive Real-Time Evaluation of the Anisotropic Thermal Diffusivity in Thin Polymer Films for Electronics Packaging
Authors: Rogers John A. , Mindas C. , Yang Y. , Nelson K. A.
Published: March 2011

We describe an experimental method capable of evaluating the in- and out-of-plane components of the anisotropic thermal diffusivity in supported and unsupported thin polymer films. The technique is used to quantify the in-plane thermal diffusivity in films of PMDA/ODA (Dupont's P12545), BTDA/ODA/MPD (Dupont's P12555), BPDA/PPD (Dupont's P12611), BCB (Dow's Cyclotene 3022) and HFDA-APBP (Amoco's UD4212) with thicknesses in the 1–10 micron range.
Raman and Photoluminescence Characterization of FIB Patterned AIGaAs/GaAs Multiple Quantum Wells
Authors: Choo Ahn Goo , Cao Xuelong. , Tlali Spirit , Jackson Howard E. , Chen Peter , Steckl Andrew J. , Boyd Joseph T.
Published: March 2011

Raman and photoluminescence (PL) spectra have been used to characterize A10.3Ga0.7As/GaAs multiple quantum well (MQW) structures that have been patterned by focused ion beam (FIB) implantation followed by rapid thermal annealing (RTA). Microprobe Raman scattering is used to identify the appropriate RTA and FIB implantation conditions that provide for removal of implantation-induced damage and for compositional intermixing. FIB patterned wire-like structures are characterized by spatially resolved PL spectra.
Photoreflectance Characterization of InGaAs/GaAs Superlattices Grown on [111]-Oriented Substrates
Authors: Rodrigues R. G. , Yang K. , Schowalter L. J. , Borrego J. M.
Published: March 2011

We report the results of a photoreflectance (PR) study of InGaAs/GaAs strained-layer quantum wells and superlattices (SLSs) grown by MBE on [111]B GaAs substrates. Under our measurement conditions, the PR spectra display features we can relate to the bandgaps of both materials and to optical transitions in the quantum structures. Using the photovoltaic effect to vary the surface electric field of our i-n+ and p+-i-n+ samples in a strictly contactless manner, we find optical transitions red-shifting with increasing intensity of illumination from a CW HeNe laser in [111]-grown structures, a well known effect which can be attributed to the straingenerated electric field (SGEF) present in these structures. We also find experimental support for the predicted effectiveness of free-carriers in screening the SGEF and thereby originating highly non-linear absorption.
Photoreflectance Characterization of InGaAs Lattice Matched to InP
Authors: Bellani V. , Amiotti M. , Geddo M. , Guizzetti G. , Landgren G.
Published: March 2011

We measured photoreflectance (PR) spectra at different temperatures between 80 and 300 K, and optical absorption (OA) at 3 K on MOVPE grown Inl-xGaxAs nearly lattice-matched to InP. x-ray diffraction measurements gave a lattice mismatch δa/ao = -0.9.10−3 between ternary alloy and InP, corresponding to × = 0.485. We obtained the energy gap dependence on T from PR spectra. The blue shift of the gap was accounted for in terms of compositional difference with respect to the perfectly lattice matched alloy (× = 0.472), and elastic strain; moreover PR and OA showed evidence of the valence bands splitting at k = 0 due to interfacial strain, in fine agreement with theory.
Room Temperature Measurement of Photoluminescence Spectra of Semiconductors Using an Ft-Raman Spectrophotometer
Authors: Webb J. D. , Dunlavy D. J. , Ciszek T. , Ahrenkiel R. K. , Wanlass M. W. , Noufi R. , Vernon S. M.
Published: March 2011

This paper demonstrates the utility of a Fourier transform (FT) Raman spectrophotometer in obtaining the room-temperature photoluminescence (PL) spectra of semiconductors used in photovoltaic and electro-optical devices. Sample types analyzed by FT-PL spectroscopy included bulk silicon and films of copper indium diselenide (CuInSej), gallium indium arsenide (GaInAs), indium phosphide arsenide, (InPAs), and gallium arsenide-germanium alloy (GaAsGe) on various substrates. The FTIR-PL technique exhibits advantages in speed, sensitivity, and freedom from stray light over conventional dispersive methods, and can be used in some cases to characterize complete semiconductor devices as well as component materials at room temperature. Recent innovations that improve the spectral range of the technique and eliminate instrumental spectral artifacts are described.
Application of Ftir Spectroscopy to the Characterization of as-Deposited and Chemical Mechanical Polished (CMP) Electron Cyclotron Resonance (ECR) Plasma Based SiO2 Films
Authors: Desai Mukesh , Carpio Ron , Jairath Rahul , Stell Matt , Tolles Robert
Published: March 2011

FTIR spectroscopy has been used to characterize as-deposited and chemical mechanical polished (CMP) electron cyclotron resonance (ECR) plasma based SiOx films. The ECR films were deposited at different O2/SiH4 gas ratios in an attempt to vary the film stochiometry. Transmission and reflectance-absorbance IR spectral data were combined with CMP removal rate information to characterize the SiOx films and their polishing behavior. The asymmetric O-Si-O stretching (ASM) and Si-OH vibrational bands were found to be principal sources of information.
Characterization of Polysilicon Films by Raman Spectroscopy and Transmission Electron Microscopy: a Comparative Study
Authors: Tallant David R. , Headley Thomas J. , Medernach John W. , Geyling Franz
Published: March 2011

Samples of chemically-vapor-deposited sub-micrometer-thick films of polysilicon were analyzed by transmission electron microscopy (TEM) in cross-section and by Raman spectroscopy with illumination at their surface. TEM and Raman spectroscopy both find varying amounts of polycrystalline and amorphous silicon in the wafers. Raman spectra obtained using blue, green and red excitation wavelengths to vary the Raman sampling depth are compared with TEM crosssections of these films. Some films have Raman spectra with a band near 497 cm−1, corresponding to numerous nanometer-scale faulted regions in the TEM micrographs.
Characterization of Interfacial Structure of InGaAs/InP Short Period Superlattices by Raman Scattering and High Resolution X-Ray Diffraction
Authors: Mozume Teruo
Published: March 2011

The x-ray diffraction (XRD) of InGaAs/InP short-period superlattices (SPSL's) grown on (001)InP substrates by gas source molecular beam epitaxy (GSMBE) and by gas source migration enhanced epitaxy (GSMEE) shows that the GSMBE grown SPSL is strain free, and that GSMEE grown SPSL's with InGa-P and In-As heterointerfaces have strain-induced zerothorder satellite peak shift consistent with that in simulation results for the InGaAs/InP SPSL with one monolayer of InGaP and InAs inserted in each interface. Partial destruction of the long-range order is confirmed by the observation of the extra diffraction peak in GSMBE grown SPSL and by weak intensity of satellite peaks and nonuniform spacing between satellite peaks in GSMEE grown SPSL's. Raman scattering shows that the strain is accommodated in the interface layer in GSMEE grown samples. A confinement model without interface disorder fits the GaAs LO phonon very well. These results indicate that the local atomic arrangements are tailored by GSMEE, but that long range-order is impaired by the misfit dislocations in GSMEE grown SPSL's and by the exchange between As to P at the interfaces in GSMBE grown SPSL.
Relating Photoresist Etch Characteristics to Langmuir Probe Measurements in an Electron Cyclotron Resonance Source
Authors: Sung K. T. , Juan W. H. , Pang S. W. , Dahimene M.
Published: March 2011

In this work, Langmuir probe measurements were used to characterize a multipolar electron cyclotron resonance (ECR) plasma source. This system has many controllable parameters including microwave power, rf power, gas, pressure, flow rate, and source distance. Both double and triple Langmuir probes were used for the plasma characterization. The results from the Langmuir probe measurements were correlated to the etch characteristics of photoresist. Ion density and photoresist etch rate were found to increase with microwave power but decrease with source distance. However, rf power does not have significant influence on ion density although the photoresist etch rate increases substantially with if power. Ion density first increases then decreases at higher pressure. Maximum ion density occurs at lower pressure for larger distance below the ECR source. Ion density uniformity for an O2 plasma is ±2% across a 16 cm diameter region at 23 cm below the source. For photoresist etched at 10 cm source distance, etch rate uniformity is ±2% for a 15 cm diameter wafer. The results from the Langmuir probe measurements indicate that photoresist etching is enhanced by ion density and ion energy.
Surface Reactivity of Silicon and Germanium in CF4 -O2 Reactive Ion Etching
Authors: Cardinaud Christophe , Campo A. , Turban G.
Published: March 2011

Reactive ion etching of silicon and germanium in CF4 -O2 was investigated. Above 20% O2 germanium etching is selective with respect to silicon. In agreement with the evolution of the fluorine and oxygen concentration in the plasma and of the etch products formation rate, surface analysis reveals that the growth of a SiOxFy layer slows down the silicon etching whereas the formation of GeOxFy does not inhibit germanium etching. Using a simple kinetic model, the silicon and germanium reactivity and its dependency with respect to the plasma composition are expressed in function of the experimental data. Results suggest that surface composition controls silicon etching, whereas germanium etching depends only on the fluorine flux on the surface.
In Situ Substrate Temperature Measurement During MBE by Band-Edge Reflection Spectroscopy
Authors: Roth J. A. , Lyon T. J. De , Adel M. E.
Published: March 2011

The use of band-edge reflection spectroscopy (BRS) to determine the substrate temperature during MBE is reviewed. Data are presented for Si, GaAs, InP and CdZnTe substrates, and the use of BRS during the growth of ZnTe on Si is demonstrated. We discuss complications that arise due to optical interference in the epitaxial layers, and methods to compensate for the effects of interference are described.
Trapping of Molecular Hydrogen in Porous Silicon and at Si/SiO2 Interfaces and a Possible Reinterpretation of the Pb Center
Authors: Stallinga Peter , Gregorkiewicz T. , Ammerlaan C.A.J.
Published: March 2011

Many recent studies of the highlighted problem of visible-range photoluminescence of porous silicon (po-Si) indicate the presence of hydrogen in this material. However, its actual role is not clear with the discussed possibilities ranging from passivation of the surface defects to some form of active participation in the photoluminescence (PL) mechanism itself. At the same time, in several magnetic resonance studies of po-Si the so-called Pb center, originally identified with the <111>-directed silicon broken bond stabilized at Si/SiO2 interfaces, has been reported.

Very recently the paramagnetic state of molecular hydrogen in bulk silicon has been identified. The spin-Hamiltonian parameters of the related Si-NL52 EPR spectrum appear to be identical to those of the Pb center. This observation casts severe doubts on the original interpretation of the Pb center while, on the other hand, offering new evidence of a prominent presence of hydrogen molecules both in po-Si and at the Si/SiO2 interface. In this paper the similarities of Si-NL52 and Pb centers are examined in detail, and it is argued that the centers are the same. It is concluded that many features of the Pb center which could not be explained within the broken-bond model can be understood with the interstitial hydrogen molecule model.
Spectroscopic Ellipsometry Characterisation of Thin Film Polysilicon
Authors: Lynch S. , Spinelli L. , Sherlock M. , Barrett J. , Crean G.M.
Published: March 2011

Phase modulated Spectroscopic Ellipsometry (SE), in the spectral range from 1.5eV to 4.6eV, was employed to characterise thin film polysilicon (poly-Si) deposited by Low Pressure Chemical Vapour Deposition (LPCVD) on SiO2/Si(100) substrates as a function of process parameters. The LPCVD deposition temperature was varied from 550°C to 620°C for silane pressures ranging from 100mTorr to 230mTorr. A variation in poly-Si microstructure was observed as a function of film depth. The influence of deposition conditions on poly-Si surface morphology was quantified using both atomic force microscopy (AFM) and SE. An increase in the measured Raman TO phonon amplitude was observed for the 620°C sample set as a function of increasing LPCVD process pressure.
Determination of Hydrogen in Semiconductors and Related Materials by Cold Neutron Capture Prompt Gamma-Ray Activation Analysis
Authors: Paul Rick L. , Lindstrom Richard M.
Published: March 2011

A reliable nondestructive method for measuring trace amounts of hydrogen in semiconductors and related materials has long been needed. Cold neutron capture prompt γ-ray activation analysis (CNPGAA) is a nondestructive, multielement technique which has found application in the measurement of trace amounts of hydrogen. The sample is irradiated by a beam of “cold” neutrons; the presence of hydrogen is confirmed by the detection of a 2223 keV gamma-ray. The technique gives bulk analyses (the neutron and gamma radiation penetrate the sample), the hydrogen peak is free of interferences, and the results are independent of the chemical form of hydrogen present. The instrument is capable of detecting less than 10 mg/kg of hydrogen in many matrices. We have used the technique to measure hydrogen levels in a dielectric film on a silicon wafer, semiconductor grade germanium, and quartz.
Characterization of Reactive Ion Etch Damage in GaAs by Triple Crystal X-Ray Diffraction
Authors: Wang Victor S. , Matyi Richard J. , Nordheden Karen J.
Published: March 2011

Triple crystal x-ray diffraction (TCXD) is a non-destructive structural characterization tool capable of the separation and direct observation of the dynamic (perfect crystal) and the kinematic (imperfect crystal) components of the total intensity diffracted by a crystal. Specifically, TCXD can be used to measure the magnitude of the diffuse scattering arising from defects in the crystal structure in the immediate vicinity of a reciprocal lattice point. In this study, the effects of BC13 reactive ion etching (RIE) on the near-surface region of GaAs were investigated by analyzing the changes in the diffuse scattering using both the symmetric 004 reflection as well as the highly asymmetric and more surface sensitive 113 reflection. While the results from the 004 reflections revealed little difference between the unetched and the BC13-etched samples, maps of the diffracted intensity around the 113 reflections showed an unexpected and reproducible decrease in the extent of the diffuse scattering in the transverse direction (perpendicular to the < 113 > direction) as the RIE bias voltage was increased. This decrease suggests that the degree of etch damage induced in the GaAs near-surface region is reduced with increasing bias voltage and ion energy. Additionally, the symmetry and orientation of the kinematic scattering was altered. Possible mechanisms for these results willbe discussed.
New Algorithms for Rapid Full-Wafer Mapping by High Resolution Double Axis X-Ray Diffraction
Authors: Loxley N , Cockerton S , Cooke L M , Gray T , Tanner B K , Bowen D K
Published: March 2011

We describe successful algorithms for rapid alignment of the Bragg planes normal to the incidence plane in a high resolution X-ray diffraction experiment. One is appropriate to the surface symmetric geometry and uses a technique of rotation about the specimen normal.

From an experimental study of the rocking curve shape as a function of tilt, we have developed a new algorithm which uses tilting about an axis formed by the intersection of the specimen and incidence planes. This has been shown to be reliable for rapid optimization of the diffraction conditions for wafers cut up to 15° off the (001) plane and for asymmetric reflections. Additionally algorithms are outlined which permit rapid location of the maximum of the Bragg peak and deduction of the mean wafer curvature from the X-ray data
Ultra-Smooth Dry Etching of GaAs Using a Hydrogen Plasma Pretreatment
Authors: Shul R. J. , Choquette Kent D. , Howard A. J. , Rieger D. J. , Dirubio C. A. , Freund R. S. , Wetzel R. C.
Published: March 2011

We have attained extremely smooth etched surfaces on GaAs using a hydrogen plasma pretreatment before etching. The resultant morphology exhibits smooth surfaces since the etching proceeds uniformly through the GaAs without micromasking effects arising from a nonuniform surface oxide. We report the effects of hydrogen plasma treatments before RIE of GaAs in two different reactors using a SiCI4 plasma. Optimization of H2 plasma pretreatments has produced improvements in RMS roughness greater than 1 order of magnitude (22.4 to 1.51 nm).
Reflectance Anisotropy and Spectroscopic Ellipsometry Characterisation of Wet Silicon Wafer Cleaning
Authors: Beechinor J. T. , Kelly P.V. , Crean G.M.
Published: March 2011

Silicon surfaces cleaned using standard wet chemical processes used in silicon device fabrication have been characterised by two optical techniques, spectroscopic ellipsometry (SE) and reflectance anisotropy spectrometry (RAS). Standard peroxide-based Si(100) wafer cleans were studied by SE. It is demonstrated that the residual film on the Si surface is critically dependent on both the sequence and type of cleaning steps performed. The sensitivity of RAS performed on-line under an air ambient to HF etched Si(110) and 4° off axis Si(100) surfaces is evaluated in comparison with kinetic SE data.
Process Monitoring for Fabrication of Mercuric Iodide Room Temperature Radiation Detectors
Authors: Van Scyoc J. M. , Schlesinger T. E. , Yao H. , James R. B. , Natarajan M. , Bao X. J. , Iwanczyk J. S. , Patt B. E. , van den Berg L.
Published: March 2011

In the fabrication of mercuric iodide room temperature radiation detectors, as in any semiconductor process, the quality of the final device can be very sensitive to the details of the processing steps. Each processing step can either reduce the intrinsic defects and those extrinsic defects introduced by earlier steps, or it can introduce new defects. In mercuric iodide these defects can act as trapping and recombination centers, thereby degrading immediate device performance or leading to long-term reliability problems. With careful study and monitoring of each step, the process can be modified to improve the end product. In this work we used several techniques to study processing steps and their effects. Photoluminescence spectroscopy and photoionization revealed defects introduced during processing. One critical step is the formation of electrical contacts, as both the material choice and deposition method have an impact. Four point probe sheet resistance methods were used to characterize the loss of material from the contact as it reacted with or moved into the bulk semiconductor. Ellipsometry was used to characterize the intrinsic optical functions of the material, and to study the effects of surface aging on these functions. Results from this work provide suggestions for the modification and monitoring of the detector fabrication process.
Characterization of Electronic Materials by Optical Reflectance Spectroscopy and Digital Signal Processing
Authors: Swart Pieter L.
Published: March 2011

Ion implantation, diffusion, epitaxy, oxidation and ion exchange are common processing steps which alter the refractive index of dielectric media. These changes can be probed non-destructively by optical methods such as infrared and ultraviolet-visible spectroscopy, and related to material structure. An overview is given of the bilinear transform of reflectance and its use in conjunction with Fourier spectral analysis for thickness and refractive index estimation. Closed-form solutions are presently available for the bilinear transformed reflectance of heteroepitaxial multilayer structures, and for materials containing graded refractive index profiles. Salient features such as positions of interfaces and refractive index steps in multilayer media; depth and width of buried inhomogeneous layers; and width of a transition region between layers of constant refractive index can be determined directly. Under certain restrictive assumptions the bilinear transformed reflectance is shown to be invertible, which allows one to determine the complete refractive index profile. Examples are presented which illustrate the determination of thickness and refractive index of individual layers in multilayered structures. Specific examples include silicon-on-insulator, and Il-V heteroepitaxial structures such as InP/InGaAs/lnP. Analysis of the reflectance of medium to high energy implanted Si or GaAs allows determination of mean damage depth and standard deviation. The invertibility of the bilinear transformed reflectance is illustrated by estimating the refractive index profile of nitrogen implanted silicon.
Phosphorus-Vacancy-Related Deep Levels in Gainp Layers Grown by Molecular Beam Epitaxy
Authors: Huang Z.C. , Wie C.R. , Varriano J.A. , Koch M.W. , Wicks G.W.
Published: March 2011

Deep levels in lattice matched Ga0.51In0.49P/GaAs heterostructure have been investigated by thermal-electric effect spectroscopy(TEES) and temperature dependent conductivity measurements. Four samples were grown by molecular beam epitaxy with various phosphorus (P2) beam equivalent pressure(BEP) of 0.125, 0.5, 2, and 4×10−4 Torr. We report for the first time, to our knowledge, an electrical observation of phosphorus vacancy point defects in the GaInP/GaAs material system. The phosphorus vacancies, Vp. behave as an electron trap which is located at EC−0.28±0.02 eV. We have found that this trap dominates the conduction band conduction when T> 220K, and is responsible for the variable-range hopping conduction when T < 220K. Its concentration decreases with the increasing phosphrous BEP. Successive rapid thermal annealing showed that its concentration increases with the increasing annealing temperature. Another electron trap at EC−0.51eV was also observed only in samples with P2 BEP less than 2×10−4 Torr. Its capture cross section is 4.5×10−15 cm 2 as obtained from the illumination time dependent TEES spectra.
Electronic Characterization of Dislocations in Rtcvd Germanium-Silicon/Silicon Grown by Graded Layer Epitaxy
Authors: Grillot P.N. , Ringel S.A. , Watsona G.P. , Fitzgerald E.A. , Xie Y.H.
Published: March 2011

Carrier trapping and recombination activity have been studied with DLTS and EBIC in RTCVD grown compositionally graded Ge0.3Si0.7/Si heterostructures. DLTS peak height is found to vary with applied bias, and the bias conditions used indicate that at least one peak is present in the homoepitaxial Si buffer layer and perhaps the substrate as well. Variations in EBIC contrast as a function of reverse bias, and DLTS fill pulse experiments both indicate that the DLTS peaks observed are dislocation related. Moreover, the bias dependent decrease in DLTS peak height is observed to occur at different rates for different peaks, indicating a possible connection between certain DLTS peaks and dislocation orientation or type. Activation energies of one electron trapping center and one hole trapping center add up to roughly the expected bandgap in a relaxed GexSi1−x, alloy with x ≦ 0.3, indicating that the electron and hole trapping centers observed with DLTS may, in fact, be associated with the R-G center observed by EBIC.
Structural Defects in Partially Relaxed InGaAs Layers
Authors: Maigne P. , Baribeau J.-M. , Roth A.P. , Boong C.L.
Published: March 2011

The development of novel optoelectronic devices using thick, defect free, strain free buffer layers mismatched to the substrate requires an understanding of the mechanisms responsible for the relaxation of the elastic strain. Using X-ray diffraction, we have studied the structural properties of partially relaxed InGaAs layers as a function of thickness and substrate misorientation and measured the residual strain. This study shows that strain free layers are difficult to achieve even for thicknesses well above the critical layer thickness. Our measurements also show that the relaxation of the strain induces geometrical effects such as a triclinic distortion of the epilayer unit cell and a tilt with respect to the substrate. These deviations from the ideal structure may seriously degrade the quality of optoelectronic active layers grown on relaxed lnGaAs buffer layers.
Deep Level Characterization of LP-MOCVD Grown Al0.48In0.52As
Authors: Ducroquet F. , Guillot G. , Hong K. , Hong C.H. , Pavlidis D. , Gauneau M.
Published: March 2011

Deep levels in unintentionally doped A10. 48In0.52As layers epitaxially grown on InP substrates by low-pressure MOCVD have been investigated as a function of growth temperature (Tg ranging from 570 to 690°C). Two different origins for the residual carrier concentration are deduced depending on Tg: i) low growth temperatures favor the creation of a deep donor located at Ec-(0.13±0.04)eV; ii) At higher Tg, a preferential incorporation of a shallow donor occurs, which can be attributed to silicon by SIMS measurements. The oxygen contamination deduced by SIMS and the electrical characteristics of the AlInAs layers do not appear to be correlated.
Hydrogen Passivation Effects in Heteroepitaxial InSb Grown on GaAs by Lpmocvd
Authors: Yoo Byueng-Su , Kim Sang-Gi , Lee El-Hang
Published: March 2011

The effects of hydrogen plasma exposure upon electron Hall mobilities in InSb heteroepitaxial film grown on GaAs substrate have been investigated. After exposure to a hydrogen plasma at 250°C, the electron Hall mobility is significantly increased at low temperatures and the temperature dependence of the mobility is reduced. For the film with a broad x-ray rocking-curve width, 4 h-hydrogen plasma exposure can give rise to the enhancement of the mobility up to 6 times at low temperature. The mobility for the film with a narrow line width is enhanced around 1.5 times. These enhanced mobilities are nearly restored by 350°C rapid thermal annealing. The enhancement of the mobility due to hydrogenation is attributed to the satisfaction of the dangling bonds generated by the misfit dislocations.
Deep Levels in Type-II Superlattices
Authors: Dow John D. , Shen Jun , Ren Shang Yuan , Packard William E.
Published: March 2011

Quantum confinement in superlattices affects shallow levels and band edges considerably (length scale of order 100 Å), but not deep levels (length scale of order 5 Å). Thus by band-gap engineering, one can move a band edge through a deep level, causing the defect responsible for the level to change its doping character. For example, the cation-on-anion-site defect in AlxGa1−xSb alloys is predicted to change from a shallow acceptor to a deep acceptor-like trap as the valence band edge passes through its T2 deep level with increasing At alloy content x. In a, Type-II superlattice, such as InAs/AlxGa1−xSb for x>0.2, where the conduction band minimum of the InAs should lie energetically below the antisite defect's T2 level in bulk AlxGa1−xSb, the electrons normally trapped in this deep level (when the defect is neutral) remotely dope the InAs n-type in the superlattice, leaving the defect positively charged. Thus a native defect that is thought of as an acceptor can actually be a donor and control the n-type doping of InAs quantum wells. The physics of such deep levels in superlattices and in quantum wells is summarized, and related to high-speed devices.
Pressure Ratio (PAs/PGa) Dependence on Low Temperature GaAs Buffer Layers Grown by MBE
Authors: Lagadas M. , Hatzopoulos Z. , Calamiotou M. , Kayiambaki M. , Christou A.
Published: March 2011

We have investigated the influence of the pressure ratio (PAs4/PGa) on the structural and electrical properties of GaAs layers grown at 250°C by MBE. SEM photographs have revealed smooth surfaces for PAs4/PGa≥15 and Double crystal X-ray rocking curves have shown an increase on the lattice mismatch δaI/a of the L.T. grown layers and high crystalline quality. Resistivity has not been affected by the different values of PAs4/PGa. n-GaAs epilayers grown on top of L.T. buffer layers have their mobility decreased and the electron trap density increased as revealed by Hall and DLTS measurements.
Effects of Impurities on the Optical Properties of Quantum Dots, Wires, and Multiple Wells
Authors: Bryant Garneit W.
Published: March 2011

Identifying and understanding the effects of impurities and defects in quantum dots, wires, and multiple wells is important for the development of nanostructures with good optical properties. Simple model calculations are presented to show when and how shallow impurities affect the radiative recombination of confined electron-hole pairs. Results for nanostructures are compared with results for bulk systems. Qualitative differences between bulk and confined systems are described.
Optical Investigation of Strained-Layer GaInAs/GaInAsP Heterostructures
Authors: Queisser I. , HÄrle V. , DÖrnen A. , Scholz F.
Published: March 2011

We performed low temperature photocurrent and photoluminescence excitation spectroscopy on tensile and compressively strained GaxIn1-xAs/GaInAsP quantum well layers to determine the band offset of the heterojunction (0.3 <XGa < 0.7). The ratio of the conduction band discontinuity to the heavy hole discontinuity has been obtained from well to barrier transitions and is found to be about 35/65 for gallium contents between 0.4 and 0.6. We obtained the effective heavy hole mass by comparison of PLE transition energies with calculations of the subband levels. We observe that the effective heavy hole mass increases with the gallium content from 0.3 m0 for XGa = 0.31 to about 0.45m0 for XGa = 0.55.
Magnetooptical Studies of Acceptors Confined in GaAs/AIGaAs Quantum Wells
Authors: Holtz P.O. , Zhao Q.X. , Monemar B. , Pasquarello A. , Sundaram M. , Merz J.L. , Gossard A.C.
Published: March 2011

Magnetooptical studies have been performed on the shallow Be acceptor confined in the central region of narrow GaAs/AlGaAs quantum wells (QWs) with the magnetic field along the growth direction. The magnetic field dependence of the acceptor transition between the 1S(Г6) hh-like ground state and the excited hh-like 2S(Г6) state has been investigated by means of two independent techniques: Two-hole transitions of the acceptor bound exciton (BE) and resonant Raman scattering. The 1S(Г6) – 2S(Г6) transition energy as a function of the magnetic field has been measured for central acceptors in QWs of widths in the range 50 – 150 Å. The energy levels for the 1S ground states and 2S excited states of the confined acceptor with a magnetic field as a perturbation have also been calculated. These calculations predict a larger splitting between the mj=+3/2 and mj=−3/2 components of the acceptor 1S(Г6) ground state in comparison with the corresponding splitting of the excited 2S(Г6) state. The experimental results are in good agreement with the theoretical predictions derived without any fitting parameters. Furthermore, the Zeeman splitting of the acceptor BE emission has been measured and it is concluded that the J = 5/2 BE state is lowest in energy, similar to shallow acceptor BEs in bulk GaAs.
Hot Filament Assisted CVD of Titanium Nitride Films
Authors: Deshpande Sadanand V. , Gulari Erdogan
Published: March 2011

Titanium nitride thin films have been deposited using a novel Hot Filament Chemical Vapor Deposition (HFCVD) technique. In this technique, a resistively heated tungsten wire (∼1700°C) is used to decompose ammonia to obtain highly reactive nitrogen precursor species. This approach allows for low temperature deposition of nitride thin films. In the past, we have used this method to deposit good quality silicon and aluminum nitride films. Titanium nitride thin films have been deposited on Si(100) at substrate temperatures from 500°C to 600°C. These films were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction, Rutherford backscattering spectroscopy (RBS) and scanning electron microscopy. The effects of deposition pressure, substrate temperature and titanium chloride flow rate on film properties have been studied. TiN films with resistivities as low as 80.0 μΩ-cm have been deposited. RBS analysis indicates that the films serve as excellent diffusion barriers for copper and aluminum metallization on silicon.
The Development of CVR Coatings for PBR Fuels
Authors: Barletta Robert. E. , Vanier P. E. , Dowell M. B. , Lennartz J. A.
Published: March 2011

Particle bed reactors (PBRs) are being developed for both space power and propulsion applications. These reactors operate with exhaust gas temperatures in the range of 2500 to 3000 K and fuel temperatures which may be hundreds of degrees higher. One fuel design for these reactors consists of uranium carbide encapsulated in either carbon or graphite. This fuel kernel must be protected from the coolant gas, usually H2, both to prevent attack of the kernel and to limit fission product release. Refractory carbide coatings have been proposed for this purpose. The typical coating process used for this is a chemical vapor deposition. Testing of other components have indicated the superiority of refractory carbide coatings applied using a chemical vapor reaction (CVR) process, however technology to apply these coatings to large numbers of fuel particles with diameters on the order of 500 gim were not readily available.

A process to deposit these CVR coatings on surrogate fuel consisting of graphite particles is described. Several types of coatings have been applied to the graphite substrate. These include NbC in various thicknesses and a bilayer coating consisting of NbC and TaC with a intermediate layer of pyrolytic graphite. These coated particles have been characterized prior to test and the results of this characterization will be presented.
New Chemical Approaches to Synthesize Titanium Disulfide
Authors: Sriram Mandyam A. , Kumta Prashant N.
Published: March 2011

The synthesis of oxides by the use of metal alkoxides is well known in the sol-gel process. However, little is known regarding the use of alkoxides as starting materials for nonoxides. In this work titanium isopropoxide has been reacted with different sulfidizing agents to form alkoxy sulfide precursors. In all the processes the transformation of the precursors to form TiS2 has been studied and the morphologies of the sulfide powders have also been compared. Gas chromatography and infrared spectroscopy have been used to study the molecular processes that occur in one of the reactions.
Properties and Potential Areas of Application
Authors: Rempel Andrei A. , Gusev Alexander I. , Berger Lutz-M. , Richter Volkmar
Published: March 2011

In this paper the differences of properties of stoichiometric and nonstoichiometric IVBand VB-Group carbides will be discussed. On the base of newer investigations of their physical and chemical properties it seems to be possible to improve material properties by using them instead of stoichiometric ones in some applications.
Thermal Decomposition of a Copolymer of Methylcyclosiloxanes and Methylcyclosilazanes to Non-Oxide Ceramics
Authors: Yu Ga-Er , Finch Dudley , Edirisinghe Mohan , Parrick John , Ralph Brian , Clarkc David
Published: March 2011

A copolymer prepared using methylcyclosiloxanes and methylcyclosilazanes has been pyrolysed in N2 and a NH3/N2 mixture. Thermogravimetric analysis (TGA) in both atmospheres and thermogravimetry-Fourier transform infrared (TG-FTIR) studies in N2 are discussed. The latter results have been used to suggest a mechanism for the thermal decomposition of the copolymer.
Combustion for the Synthesis of β-SiC and Diamond/SiC Composite
Authors: Raghunathan Rohini , Chowdhury Rina , Narayan Jagdish
Published: March 2011

Cubic β-SiC was processed under conditions of self-propagating high-temperature synthesis, based on the exothermic reaction between elemental Si and C powders. The set up for the synthesis of SiC using a mixture of Si and C is described. X-Ray and Raman spectroscopy studies were performed to characterize the quality of the β-SiC produced using the new set up. Scanning Electron Microscopy and Transmission Electron Microscopy studies were also carried out to study the mechanism of the formation of β-SiC from the elemental powders. The density of the compact and grain size of the graphite was found to be critical in the formation of the SiC. Diamond seeds were also implanted on the SiC pellet while compaction and this implanted diamond provided the necessary seed for the growth of a thick diamond film. The adhesion of the film is good because of its growth from the implanted diamond. Diamond films were grown on SiC using HFCVD. The quality and the adhesion of the diamond films on SiC were studied using SEM.
Copper-Containing Ceramic Precursor Synthesis: Solid-State Transformations and Materials Technology
Authors: Hepp Aloysius F. , Eckles William E. , Duraj Stan A. , Andras Maria T. , Fanwick Phillip E. , Richman Robert M. , Sabat Michael L. , Power Michael B. , Gordon Edward M. , Barron Andrew R.
Published: March 2011

Three copper systems with relevance to materials technology are discussed. In the first, a CuS precursor, Cu4S 10(4-methylpyridine)4 (4-MePy), was prepared by three routes: reaction of Cu2S, reaction of CuBr•SMe2 and oxidation of copper powder with excess sulfur in 4-methylpyridine by sulfur. In the second, copper powder was found to react with excess thiourea (H2NC(S)NH2) in 4-methylpyridine to produce thiocyanate (NCS-) complexes. Three isolated and characterized compounds are: Cu(NCS)(4-MePy)2, a polymer, [4-MePy•H][Cu(NCS)3(4-MePy)2], a salt, and t-Cu(NCS)2(4-MePy)4. Finally, an attempt to produce a mixed-metal sulfide precursor of Cu and Ga in N-methylimidazole (N-MeIm) resulted in the synthesis of a Cu-containing polymer, Cu(S04)(N-Melm). The structures are presented; the chemistry will be briefly discussed in the context of preparation and processing of copper-containing materials for aerospace applications.
Processing and Property Evaluation of Si(N,C) Coatings on Silica Glass/Quartz Substrates
Authors: Gonsalves Kenneth E. , Xiao Tongsan D. , Strutt Peter R.
Published: March 2011

This investigation outlines a process for the synthesis of preceramic/ceramic hard coatings on glass substrates. The precursor used was an organosilazane monomer [CH3SiHNH]n, with n=3 or 4. The glass substrates were dip coated in organosilazane solutions. The coated samples were then heat treated in different gaseous environments to produce the desired preceramic and ceramic coatings. The mechanical properties of the coatings were evaluated, such as rupture strength and microhardness. The former was measured using a four-point bend test (ASTM c150). Vicker's hardness rupture strength measurement were performed on both coated and uncoated specimens subjected to the heat treatment conditions. Microstructural examination was performed using a SEM. Chemical information, such as bonding was investigated via FTIR spectroscopy.
Stresses and Adhesion of Thin Polycrystalline 3C SiC Films Grown by CVD on Silicon Substrates
Authors: Ivanova L.M. , Kovalenko V.V. , Tkacheva T.M.
Published: March 2011

SiC thin films less than 1 μm thick are grown by thermal decomposition of CH3SiC13 in a hydrogen atmosphere in an open CVD system. The interface stress is shown to be depend on the growth conditions. The optimal conditions for the preparation of uniform SiC films have been determined. Thermal annealing of the films has also been studied, and the conditions that provide for relaxation of the interface stresses are determined.
Surface and Bulk Interactions in M-SiC Systems (M = Au, Cu, Ni).
Authors: Rado C. , Kalogeropoulou S. , Eustathopoulos N.
Published: March 2011

Surface and bulk interactions between a metal M (M = Au, Cu or Ni) and monocrystalline α-SiC are studied. Surface interactions are quantified by the work of adhesion measured by the sessile drop technique under high vacuum. Products of M-SiC bulk reactions are characterised by electron microscopy and microprobe analysis. Interpretation of experimental results is based on classical thermodynamics for equilibria of bulk phases and on interfacial thermodynamics for adsorption phenomena and wetting.
X-ray Absorption Study of Pulsed Laser Deposited Boron Nitride Films
Authors: Chaiken A. , Terminello L.J. , Wong J. , Doll G.L. , Sato T.
Published: March 2011

B and N K-edge x-ray absorption spectroscopy measurements have been performed on three BN thin films grown on Si substrates using ion-assisted pulsed laser deposition. Comparison of the films’ spectra to those of several single-phase BN powder standards shows that the films consist primarily of sp2 bonds. Other features in the films’ spectra suggest the presence of secondary phases, possibly cubic or rhombohedral BN. Films grown at higher deposition rates and higher ion-beam voltages are found to be more disordered, in agreement with previous work.
The Effect of Impurities on the Ideal Tensile Strength of Covalent Crystals - Ab-Initio Quantum Molecular Dynamics Calculations
Authors: Huang Y.M. , Spence J.C.H. , Sankey Otto F.
Published: March 2011

Using first-principles electronic structure calculations in the local density approximation combined with lattice dynamics, we investigate the effect of III/V impurities on the ideal strength of covalent solids (C, Si, and Ge). Our results show that undoped crystalline solids are stronger in tension along [111] than n-type crystalline solids. P doping has a negligible effect on ideal tensile strength, while n-type doping causes a small reduction in strength of about 6%. The n-type impurity effect is due to the negative (repulsive) contribution from the bottom state of the distorted conduction band to the ideal strength of the solid.
Physical Properties of Nanocrystalline MoS2 and WS2 Particles Produced by CO2 Laser Pyrolysis
Authors: Bi Xiang-Xin , Wang Ying , Lee W. T. , Wang Kai-An , Bandow S. , Eklund P. C.
Published: March 2011

Nanocrystalline powders of 2H-MoS2 and 2H-WS2 with average particle size 5 and 9 nm, respectively, have been produced using C02laser pyrolysis. Typical production rate for these nanoparticles is 2g/hr. Particle size, crystallite size, and the structural phase were determined using X-ray diffraction(XRD), transmission electron microscopy(TEM), and Raman scattering. Particle size effects may have been observed in the Raman-active modes (WS2 and MoS2) and in the band-edge excitons (MoS2).
Hafnium Nitride Dielectric Phase Films Fabricated by Ion-Beam Sputtering
Authors: Klemm Karl. A. , Johnson L. F. , Kosik W. E. , Mckenzie D. R. , Perez I. , Pontelandolfo M.
Published: March 2011

Hafnium nitride films were deposited by ion-beam sputtering, and characterized for their composition, electrical, structural, mechanical and optical characteristics. Films were found to vary widely in their properties, based upon the parameters under which they were deposited. The films were found to have a nitrogen to hafnium ratio of up to 1.45:1, resistivity varying from 10−2 to 105 Ω-cm, as well as widely variable optical characteristics, depending on process variables. Structural characterization of the dielectric phase HfNx (x>l) material by X-ray and electron diffraction reveals a distortion of the hafnium mononitride rock salt structure with increasing amounts of nitrogen, in accordance with previous findings. Infrared spectroscopic characterization of the thin film dielectric phase hafnium nitride optical properties reveals the likely existence of multiple bonding between nitrogen in the material.
Nonthermochromic Forms of the Polydiacetylene ETCD
Authors: Sandman Daniel J. , Downey Milton J. , Hankin Sandra H.W.
Published: March 2011

Subjecting crystals of the thermochromic polydiacetylene (PDA) from the bis (ethyl ure thane) of 5,7-dodecadiyne-1, 12-diol (ETCD) to the solvents chlorobenzene and ?,?-dimethylformamide above the thermochromic transition temperature of PDA-ETCD irreversibly converts the material to nonthermochromic forms. These new forms have been characterized by their structural, thermal, and spectral properties. The materials isolated after exposure to chlorobenzene are highly crystalline with a structure that has expanded and disordered, yet is still related to that of the pristine polymer. The observed properties are discussed in the framework of the crystal structure-thermochromism relationship for urethane-substituted PDA.
The Metallic State of Conducting Polymers: Microwave Dielectric Response and Optical Conductivity
Authors: Epstein A. J. , Joo J. , Kohlman R. S. , Macdiarmid A. G. , Weisinger J. M. , Min Y. , Pouget J. P. , Tsukamoto J.
Published: March 2011

Recent advances in processing of polyaniline and polyacetylene have resulted in a new generation of conducting polymers with higher dc conductivities. We present the temperature (T) dependent microwave frequency dielectric constant, dc conductivity, and Kramers-Kronig analysis of conducting polyaniline and polyacetylene. The low temperature dielectric constant, ε, increases with the square of the x-ray crystalline domain length for preparations of HCl protonated polyaniline. For the highest crystalline polyaniline samples, ε increases dramatically with increasing T, supporting formation of three-dimensional (3-D) coupled “mesoscopic” Metallic regions. A “metallic” negative ε is observed for d,1-camphor sulfonie acid doped polyaniline prepared in m-cresol. Optical studies show a linear increase in reflectivity below 7000 cm-1. Below 600 cm-1 the reflectance increases rapidly. Kramers-Kronig analysis of the ir-visible results are presented. Highly conducting polyaniline is shown to have two plasma frequencies, one at ∼ 1.1 eV involving all the conduction band electrons, and one at ∼0.015 eV (120 cm-1) that is suggested to arise from the most delocalized electrons. The concept of inhomogeneous disorder is introduced. The results for polyaniline are compared to those of highly doped polyacetylene which also show metallic negative ε demonstrating the intrinsic metallic nature of the new generation of conducting polymers.