bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid densification of borophosphosilicate glass
Authors: Madsen Lynnette D. , Mercier Jacques S.
Published: April 2011

The effect of densification, using a rapid thermal annealer, on properties of low pressure chemical vapor deposited borophosphosilicate glass films (4 wt.% B, 4 wt.% P) has been investigated. After densification, the wet etch rate of the films decreased by a factor of 12, while the infrared Si–O band peak height increased by 10%. Application of these findings to process monitoring and the impact of densification on subsequent processing have been examined. Results show that a single densification cycle at 950 °C/20 s induces glass flow behavior. Furthermore, for densification cycles from 500 to 1000 °C for 20 s followed by a fusion cycle of 1100 °C/20 s, densification temperature has no effect on the smoothing of glass over step structures. However, for contact sidewalls a densification cycle of at least 700 °C/20 s is required for sufficient tapering of the sharp corner. An optimal densification cycle for device processing was determined to be 800 °C/20 s.
Fabrication of devices using vacuum deposited a–Si
Authors: Audas R. D. , Brodie D. E.
Published: April 2011

The long-term objective of this work is to produce a stable, efficient amorphous Si (a-Si) solar cell by a safe and inexpensive method. A process of reactive evaporation in a silane ambient was developed. This technique permits the fabrication of "intrinsic-like" a-Si:H. p-Type and n-type samples (carrier type was confirmed by Seebeck measurements) were prepared by the coevaporation of boron or reactive evaporation in a phosphorus ambient. The intrinsic-like samples have a room temperature conductivity of about 2 × 10−12 S cm−1, high temperature activation energies of 0.9 eV, and optical bandgaps near 1.8 eV. An all-amorphous Si:H pin diode was fabricated using this reactive evaporation process. The device consists of a tantalum contact, 20 – 40 nm of phosphorus doped a-Si:H, 300 – 400 nm of undoped a-Si:H, 20 – 40 nm of boron doped a-Si:H, and another tantalum contact.
Influence of surface effects on the sensitivity of magnetic-field sensors
Authors: Ristić LJ. , Truong T. Q. , Doan M. , Mladenovic D. , Baltes H. P.
Published: April 2011

A comparative study of the role of surface effects in the sensitivity of lateral magnetotransistors and magnetodiodes is presented. The surface potential at the Si–SiO2 interface is changed by means of the gate voltage. Both types of devices are realized in standard complementary metal oxide semiconductor technology. The results indicate that improvement of the sensitivity can be achieved in both cases, but the dependence of sensitivity of magnetotransistor on surface effects is much lower than that of magnetodiode.
GaAs charge-coupled devices
Authors: Davidson D. A. , Berolo O.
Published: April 2011

This paper reports on the first Canadian involvement in the design, process development, fabrication, and evaluation of a gallium arsenide (GaAs) charge-coupled device (CCD). The project is applications driven, and is eventually expected to yield devices capable of performing at microwave frequencies with broad bandwidths. The devices were originally designed to operate in a transient digitizer for high-energy nuclear-event analysis at the the Tri- University Meson Facility (TRIUMF) in B.C.The prototype device consists of a 32-stage, four-phase GaAs CCD intended to function at radio-frequencies (if). The work that has been undertaken will be discussed under the following aspects: device design, layout description, and substrate-material specifications. This discussion will be supported by an in-depth explanation of the functioning and operation of the GaAs CCD, and how the above considerations affect it. A description will be given of the procedures, methodology, and the test-bed utilized to evaluate the devices. Results will be given for CCDs operating close to 1 GHz. The rf waveform will be analyzed in the context of charge-transfer efficiency (CTE) and the presence of clock feedthrough. Because of the need for an eventual integration of the GaAs CCD on-chip with other essential auxiliary electronic circuitry, results will be given for devices working in conjunction with other GaAs digital and analog circuits, such as a broad-band four-phase clock generator and a sample-and-hold circuit.
Electrically active multilayer n-GaAs–p-AlGaAs quarter wave mirrors grown by molecular beam epitaxy
Authors: Howard A. J. , Anderson T. J. , Larochelle S. , Bassignana I. C. , Mandeville P. , Svilans M. N.
Published: April 2011

A novel optoelectronic structure is presented, based on an optical interference filter with a stack of quarter-wave p–n heterojunctions in the GaAs–AlGaAs III–V semiconductor system. In a 40 layer structure with a peak reflectivity at 1.3 μm, good vertical period uniformity and crystalline quality was confirmed by optical reflectance peak widths, transmission electron microscope cross sections, and double crystal rocking curves. The structure is electro-optically active near the GaAs band gap and optically passive at longer wavelengths. Electrical bistability was observed. The potential device applications include electrically tunable optical filters for optoelectronic switching, modulation, and selective wavelength detection.
Reflection high-energy electron diffraction study of (111) and (001) CdTe grown on (001) GaAs by pulsed laser evaporation and epitaxy
Authors: Dubowski J. J. , Williams D. F. , Wrobel J. M. , Sewell P. B. , LeGeyt J. , Halpin C. , Todd D.
Published: April 2011

Reflection high-energy electron diffraction investigations of CdTe films grown on (001) GaAs have been carried out. The films were deposited with a pulsed laser evaporation and epitaxy system which was specially developed in order to grow thin films of AII–BVI compounds. Preparation of (001) GaAs substrates included degreasing in standard solvents, etching in a solution of H2S04–H2O2–H2O, vacuum bakeout, and ion etching. The ion etching was found to be relatively effective in obtaining a partially reconstructed surface of GaAs. The growth of (111) CdTe with [Formula: see text] GaAs took place on such a surface. Deposition on ion cleaned (001) GaAs substrates which did not show surface reconstruction resulted in the growth of (001) CdTe with [Formula: see text] GaAs. For samples thicker than ~1 μm, a (001) CdTe-(2 × 1) structure was observed.
Raman and X-ray diffraction study of relaxation in Si–Si1–xGex strained-layer superlattices
Authors: Lockwood D. J. , Baribeau J.-M. , Timbrell P. Y.
Published: April 2011

We report a study of the relaxation of Si–Si1–xGex strained single layers and superlattices by Raman scattering spectroscopy, double crystal X-ray diffraction, and transmission and scanning electron microscopy. Samples of various dimensions and compositions were produced by molecular beam epitaxy at a growth temperature of 500 ± 30 °C. The thermal stability of the various specimens was investigated by annealing experiments at temperatures between 600 and 900 °C. Considerable deterioration of the crystal quality and progressive relaxation were observed in some of the samples. Relaxation occurred through formation of misfit dislocations at the first Si–Si1–xGex interface and these caused threading dislocations to form within the epilayer. The degradation of the superlattice interfaces on annealing is correlated with a sharp decrease in the acoustic mode Raman intensities. Strain values perpendicular to the growth direction as a function of annealing temperature are obtained from a kinematical simulation of the X-ray rocking curves. These results are compared with the frequency shifts of the longitudinal optical phonons in the Raman spectra. The results obtained for the critical layer thicknesses versus x are consistent with the excess stress model of Tsao and co-workers.
X-ray photoelectron spectroscopy studies of aging effects on the surface of Au – a-Si:H – Sb-Cr Schottky diodes
Authors: Paquin L. , Wertheimer M. R. , Sacher E. , McIntyre N. S.
Published: April 2011

During investigations of Au – a-Si:H – Cr–Sb photovoltaic Schottky diodes, it was observed that photoconversion parameters (1sc, Voc, η) improved markedly with time for samples stored for several weeks in ambient air. This was always accompanied by apparent color changes in the area under the top (Au) electrode, from gold to deep purple, and by evolution of its surface conductivity (σ) from a highly conducting to an insulating state. Profilometry indicated that the colored area rose about 80 nm above the original surface during these changes. These diodes have been examined using depth-profiling surface analytical techniques, namely secondary-ion mass spectroscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy (XPS), but primarily the latter. The XPS studies of the entire layer thickness on the gold electrode were carried out using erosion by Ar+ ion bombardment. The XPS line positions were used to infer electrical properties of silicon and gold constituents.The results show that Si atoms first diffuse through the gold electrode, where they react with atmospheric constituents to form a thick layer composed mainly of SiO2. This layer is responsible for the observed changes in color, a, and 1sc. The latter change, which leads to a maximum rise in η of about 60%, is felt to result from the fact that the SiO2 layer acts as an antireflection coating. Gold from the electrode layer also diffuses outward, mixed intimately with the silicon oxide. Further aging results in a degradation of the electrical continuity of the Au electrode, which is believed to be responsible for the observed slow drop in η.
EL2 and gallium antisite defects in GaAs: Si
Authors: Teh C. K. , Weichman F. L. , Tin C. C. , Barnes P. A.
Published: April 2011

Photoluminescence (PL), Fourier-transform infrared (FTIR), and deep-level transient spectroscopy (DLTS) measurements have been made on various samples of silicon-doped liquid-encapsulated Czochralski-grown GaAs. All the samples show prominent PL peaks at 1.443 and 1.325 eV together with their longitudinal optic (LO) phonon peaks. The PL peak at 1.443 eV has been reported in the literature as being due to either GaAs or a boron-related defect. The FTIR results show the presence of BGa at 540.3 and 517.0 cm−1 and SiGa at 383.6 cm−1. We have observed that there is no correlation between the PL peak at 1.443 eV and BGa. Thus, we believe that this PL peak is related to the GaAs antisite defect. The presence of EL2 in the samples has been measured using DLTS. We have found that the intensity of the PL peak at 1.443 eV varies inversely with that of the EL2 peak. This relationship indirectly confirms that the 1.443 eV peak is due to the gallium antisite defect. The PL peak at 1.325 eV is significantly different from those reported in the literature for GaAs:Si. Measurements have also been made on samples of GaAs:Si annealed under different arsenic overpressures.
GLOSSARY
Authors: Freeman Gordon
Published: April 2011

A glossary of specialist terms speeds communication between workers in different disciplines. The definitions given here have been worked on by six interdisciplinary editorial groups and coordinated by the editor. In addition to the interdisciplinary aspect, there is a clarification of some of the concepts that some of us have been using for a long time.This Glossary and the Discussion Summaries that follow some of the papers greatly assist in the breaking down of communication barriers that tend to isolate different disciplines from each other.The Glossary terms and definitions were submitted by various authors and were selected, modified, or accepted by the editorial groups. The members of the groups, in alphabetical order were: H. Atmanspacher, F. Brochard-Wyart, J. A. Brooke, M. Daoud, P.-G. de Gennes, I. R. Epstein, D. T. Goodhead, L. Györgyi, A. Hummel, C. Jonah, J. L. Magee, L. K. Mansur, D. Möbius, J. Noolandi, R. M. Noyes, P. Oftedal, H. G. Paretzke, E. Sackmann, M. F Schumaker, P. Wesson, and D. Yuen.
Short-range-induced critical phenomena in the Landau–Ginzburg model
Authors: Tuszynski J. A. , Skierski M. , Grundland A. M.
Published: April 2011

Within the framework of the Landau–Ginzburg model of phase transitions, the type of physical behaviour that results from the sign reversal of the coefficient owing to inhomogeneities is investigated. As a result, a number of interesting phase-transition sequences are obtained. Some such sequences have been observed in metamagnets. These effects are interpreted as induced by short-range interactions.
Deterministic chaos, fractals, and quantumlike mechanics in atmospheric flows
Authors: Selvam A. Mary
Published: April 2011

The complex spatiotemporal patterns of atmospheric flows that result from the cooperative existence of fluctuations ranging in size from millimetres to thousands of kilometres are found to exhibit long-range spatial and temporal correlations. These correlations are manifested as the self-similar fractal geometry of the global cloud cover pattern and the inverse power-law form for the atmospheric eddy energy spectrum. Such long-range spatiotemporal correlations are ubiquitous in extended natural dynamical systems and are signatures of deterministic chaos or self-organized criticality. In this paper, a cell dynamical system model for atmospheric flows is developed by consideration of microscopic domain eddy dynamical processes. This nondeterministic model enables formulation of a simple closed set of governing equations for the prediction and description of observed atmospheric flow structure characteristics as follows. The strange-attractor design of the field of deterministic chaos in atmospheric flows consists of a nested continuum of logarithmic spiral circulations that trace out the quasi-periodic Penrose tiling pattern, identified as the quasi-crystalline structure in condensed matter physics. The atmospheric eddy energy structure follows laws similar to quantum mechanical laws. The apparent waveparticle duality that characterizes quantum mechanical laws is attributed to the bimodal phenomenological form of energy display in the bidirectional energy flow that is intrinsic to eddy circulations, e.g., formation of clouds in updrafts and dissipation of clouds in downdrafts that result in the observed discrete cellular geometry of cloud structure.
Self-organization in freezing soils: from microscopic ice lenses to patterned ground
Authors: Hallet Bernard
Published: April 2011

Freezing in moist fine-grained soils is a highly nonhomogeneous process. It involves transport of water to freezing sites and growth of distinct ice bodies separated by soil domains free of ice. On a much larger scale, recurrent ice growth and thawing of cold regions produce a rich diversity of patterns in soils; these patterns can be defined by local relief, soil cracks, or segregation of mineral material according to size. This paper reviews the principal spatial structures characteristic of freezing soils and discusses the underlying processes in the broader context of geomorphic self-organization.
An embedded-atom-method study of diffusion of an Ag adatom on (111) Ag
Authors: Rilling W. K. , Gilmore C. M. , Andreadis T. D. , Sprague J. A.
Published: April 2011

The activation energy, vibrational frequency, and surface-diffusion jumps of a single adatom on a perfect (111) surface were studied using the embedded-atom method. The activation energy was determined with a conjugate gradient energy-minimization procedure. The surface adatom was moved in steps across the (111) plane through a saddle point. The adatom position was fixed within (parallel to) the (111) plane; but, the Ag adatom was free to relax, normal to the (111) plane. In this way the adatom was free to ride up over the saddle point; so that at each fixed position within the (111) plane the Ag adatom was free to move to its minimum energy. Also all of the atoms within the Ag crystal were free to relax to minimum-energy positions as the Ag adatom was moved across the surface. The minimum activation energy calculated for adatom diffusion was 0.058 eV. The embedded-atom method was also combined with a molecular dynamics simulation to observe the vibrations of the surface atoms and the adatom and to observe surface-diffusion jumps of the adatom. The adatom jumped to new surface sites at a frequency of approximately 1 × 1012 jumps s−1 at a temperature of 700 K.
Nonuniformity of crack-growth resistance and breakdown zone near the propagating tip of a shear crack in brittle rock: A model for earthquake nucleation to dynamic rupture
Authors: Ohnaka Mitiyasu
Published: April 2011

This paper reviews our recent studies on (i) slip failure nucleation, which leads to the mechanical instability that gives rise to a dynamically propagating shear rupture, (ii) constitutive behavior during the local breakdown process near the propagating tip of the slipping zone, and (iii) the physical modeling of the earthquake-source process based on the constitutive relation inferred from laboratory experiments. Laboratory studies were done using a simulated fault in rock in the brittle regime under a mode II crack-growth condition, to gain a deeper understanding of the earthquake-source process, which is considered to be dynamically propagating shear rupture in the earth. A stable but accelerating phase of nucleation locally precedes an unstable dynamically propagating rupture even in the brittle regime. The appearance of a sizable zone of such nucleation is related to a nonuniform distribution of the crack-growth resistance on the fault. The local shear strength degrades to a residual friction stress level with ongoing slip near the propagating tip of the slipping zone. This slip-dependent constitutive relation shows that there is a breakdown zone near the propagating tip over which shear stress, slip displacement, slip velocity, and slip acceleration are highly nonuniform. This nonuniformity is responsible for generating high-frequency elastic radiation. A model of the breakdown zone, which incorporates the laboratory-based constitutive relation, does not give rise to unrealistic singularities of slip acceleration and stresses at and near the dynamically propagating tip of the slipping zone. The breakdown zone model enables one to give a common interpretation to both small-scale slip failure in the laboratory and large-scale shear failure as earthquake faulting in the earth, and it can explain the earthquake-source strong motion characterized by the high-frequency content.
Simulation of a simple model for aggregating telechelic ionomers
Authors: Schumaker Mark F. , Epstein Irving R.
Published: April 2011

We develop a simple model for the aggregation of telechelic ionomers by extending the well-known algorithm for particle diffusion-limited aggregation (DLA). The distribution of sticky and nonsticky regions of the polymer and specific rules for binding are incorporated. Thirteen aggregates are grown to a final size of 2441 polymers each. The distribution of accessible binding sites modifies the growth of these clusters as compared with DLA. The dynamical dimension estimated from the growth of the radius of gyration is found to have a value of 1.81 ± 0.04, significantly larger than values reported for particle DLA. However, a careful analysis of our data suggests that the dimension is nonstationary and decreasing at the largest cluster sizes attained. We have also investigated the scaling of the average mass of the cluster interface with the number of polymers and the radius of gyration. Our results suggest that the fractal dimension of the cluster interface is close to one, in agreement with previously reported findings for particle DLA.
Magnetotransistors sensitive to a magnetic field applied in two different directions
Authors: Doan M. , Ristic Lj.
Published: April 2011

A lateral magnetotransistor that is sensitive to a magnetic field applied either parallel or perpendicular to the chip's surface is reported. It is fabricated using the standard complementary metal oxide semiconductor process. The deflection of the carriers in the base region is considered as the basic principle of operation. The device shows a linear response to a magnetic field in both directions. The minimum magnetic induction to be detected is in the order of 10 μT at f = 1 kHz.
Stability and spatial characterization of electron cyclotron resonance processing plasmas
Authors: Shufflebotham P. K. , Thomson D. J.
Published: April 2011

This paper presents preliminary measurements of the spatial variation of the plasma density, electron temperature, plasma potential, and floating voltage within a divergent magnetic field electron cyclotron resonance (ECR) plasma processing reactor. The measurements are performed using an orbital-motion-limited cylindrical Langmuir probe designed specifically for use in these plasmas. A brief discussion of the stability and uniformity of divergent field plasmas in general, and qualitative techniques for the diagnosis of these properties, is also given. It was found that these plasmas generally occurred in distinct "modes," characterized by unique shapes and dependences on system variables, and between which discontinuous, noisy, and often bistable transitions occurred. Axially resolved probe measurements performed under ECR conditions showed that the plasma density exhibited a broadly peaked profile, while the electron temperature showed a sharp peak at ECR. The differences in these profiles leads to three qualitatively different plasma regions available for use in ECR processing. The variation of the plasma potential explains the origin of the axial ion beams that commonly occur in these systems.
Energy-momentum transport-based simulator adapted to the general purpose semiconductor device simulation development tool CHORD
Authors: Roberts James W. , Chamberlain Savvas G. , McMacken John R. F.
Published: April 2011

Application of the conventional drift–diffusion model to certain submicrometre devices may be inappropriate owing to hot carrier effects. These may include localized velocity saturation overshoot and impact ionization. Silicon device models based on the conservation of carrier momentum and energy have been shown to model such effects more accurately. However, to date, these energy-momentum transport (EMT)-based simulators have been limited in scope or designed for specific device application only. This paper describes the implementation of an EMT model into the modular semiconductor device simulation tool CHORD. The simulator fully couples energy-momentum transport equations for electrons and holes with the lattice heat equation in two space dimensions and time. The EMT model is designed to be consistent with the general purpose nature of the CHORD simulation system and thus can accommodate arbitrary device structure and bias conditions. A major strength in the CHORD system is that it allows for the addition of new models with minimal interface between the user and the simulator infrastructure. The addition of the EMT model to the existing set of models, already available to CHORD users, is a representative example of the procedures involved. The equations that define the EMT model are included along with results from simulations of an ultrashort channel MOSFET (metal oxide semiconductor field effect transistor) intended to highlight carrier heating and velocity saturation overshoot.
The influence of niobium-doping on lead zirconate titanate ferroelectric thin films
Authors: Griswold E. M. , Sayer M. , Amm D. T. , Calder I. D.
Published: April 2011

Ferroelectric thin films have recently proven viable for nonvolatile memory applications in semiconductor technology. Current research is focused on the development of processing technologies and deposition on metallized semiconductor substrates. In this study, niobium-doped lead zirconate titanate thin films were prepared by a dc magnetron-sputtering technique using a multielement metal target. Films were deposited on indium tin oxide coated glass and on metallizations on silicon substrates. The crystallographic structure and surface morphology of the films was examined by scanning electron microscopy and X-ray diffraction as a function of processing variables such as sputtering pressure, film thickness, and niobium content. Electrical characterization of the films is discussed in terms of ferroelectric hysteresis and polarization properties. Improved ferroelectric properties are achieved through a densified structure resulting from niobium-doping.
Photoluminescence of heavily doped GaAs and Ga0.85In0.15As
Authors: Benzaquen R. , Erland T. , Lacelle C. , Fortin E. , Roth A. P.
Published: April 2011

Zinc-doped, p-type, GaAs and Ga0.85In0.15As samples with a carrier concentration up to p = 1.95 × 1020 cm−3 were studied by low-temperature photoluminescence. At low doping levels, recombinations involving impurity states provide a measurement of the zinc-acceptor binding energy in the Ga0.85In0.15As alloy. At high concentrations, the discrete acceptor levels are replaced by an impurity band. In the presence of a high density of impurities, potential fluctuations and interparticle interactions result in a band-gap renormalization that is observed with photoluminescence experiments. This phenomenon is analyzed on the basis of available models that take into account the nonconservation of momentum for optical transitions as well as many-body effects.
Caractérisation physicochimique et électronique de la structure Pt–a-Si: H–c-Si(n)
Authors: Belkouch S. , Paquin L. , Deneuville A. , Gheeraert E.
Published: April 2011

Infrared absorption spectra, and electrical measurements I(V, T) and C(V) at 100 Hz of the Pt–a-Si:H–c-Si structure are presented. The thickness, d, of the hydrogenated amorphous silicium, a-Si:H, varies between 4800 and 180 Å(1 Å = 10−10 m). Infrared absorption measurements on a-Si:H show that with the decrease in d there is an increase in the number of defects and the hydrogen concentration on Si-H sites. The electrical results I(V, T) show a Schottky-like structure whose ideality factor increases with decreasing T, but remains limited even for small values of d (1.4 at 300 K for d = 180 Å). Two potential barriers are also deduced: at high temperature [Formula: see text] and is independent of d. This barrier is attributed to the Pt–a-Si:H interface. At low temperature, [Formula: see text] increases from 0.23 to 0.5 eV as d decreases from 2400 to 180 Å. This barrier is attributed to the a-Si = H–c-Si, interface, the transport in a-Si:H taking place by tunnelling between localized states. The C(V) measurements allow the separation between the c-Si and the a-Si:H responses. Above 100 kHz, there is no response from a-Si:H, which behaves then as a dielectric. The electrostatic potential drop in c-Si is deduced as a function of the applied voltage V for each value of d. A positive electrostatic potential is found when V = 0 for d ≤ 500 Å.[Journal translation]
Measurement of mobility-lifetime products in amorphous semiconductors
Authors: Polischuk B. , Kasap S. O. , Aiyah Viswanath , Baillie A. , Abkowitz M. A.
Published: April 2011

Charge-carrier drift-mobility-lifetime (μτ) product, the range of the carrier, is one of the most important electronic properties of a semiconductor material for device applications. The determination of μτ is, therefore, of fundamental importance in the characterization of amorphous semiconductors and has been the key issue in a number of recent papers. This paper describes two experimental techniques for μτ product measurements and their application to a-Se and Cl-doped Se:0.35%As electro-radiographic films. Xerographic measurements involve corona charging the surface of an amorphous semiconductor film to a voltage Vo. The film is then exposed to a highly absorbed step illumination at the end of which the residual potential, VR1, on the surface is measured. VR1/Vo is then related to μτ. In the interrupted field time-of-flight (IFTOF) measurement technique, during the flight of the photoinjected holes through the specimen, the applied field is removed at time T1 for an interruption duration of ti and then reapplied and the remaining holes extracted. The fractional recovered photocurrent at the end of the interruption time, ti was found to follow the deep-trapping kinetics described by i(T1 + ti)/i(T1) = exp (−ti/τ) where τ is the charge-carrier lifetime. By interrupting the time-of-flight photocurrent at different locations, the technique allows for the determination of the trapping time τ as a function of location across the specimen and hence the examination of sample inhomogeneities. Xerographic residual potential and IFTOF experiments carried out on a range of a-Se and Cl-doped a-Se:0.35%As electroradiographic films show that there is a good correlation between the trapping time determined from xerographic measurements and that determined from IFTOF. The results are discussed in terms of carrier-trapping processes in amorphous semiconductors. The capture cross section of deep hole traps in a-Se and Cl-doped a-Se:0.35%As is determined from the measurement of the hole-mobility-lifetime product and the saturated cycled-up residual potential. Application of the ballistic and diffusional models of Street (Philos. Mag. B, 49, L15 (1984)) indicate that the hole-capture radius in a-Se is 2–3 Å (1 Å = 10−1 m) and that the chemical modification of a-Se by combinational doping with 0.35%As and 10–20 ppm Cl does not affect the basic capture process. The two experimental techniques described represent the most meaningful methods of charge transport and trapping characterization in amorphous semiconductors.
Raman and infrared spectroscopy of In1−xGaxSb films grown on GaAs by metal-organic magnetron sputtering
Authors: Feng Z. C. , Perkowitz S. , Rousina R. , Webb J. B.
Published: April 2011

Thin films of the novel III–V ternary In1−xGaxSb were grown by metal-organic magnetron sputtering on (001) GaAs substrates. We used Raman scattering and infrared-reflectivity measurements to examine films of thickness 1–2 micrometres with x(Ga) = 0.0, 0.035, 0.07, 0.24, 0.32, 0.68, and 1. We observe two-mode phonon behavior over the range 0 < x < 0.7, and derive the dependence of the GaSb and InSb-like transverse and longitudinal optical phonon frequencies and intensities on Ga composition. The Raman line widths at half maximum are < 10 cm−1 and the polarization behavior of the Raman spectra obeys the selection rules for a (001) surface, indicating that the films are of good crystalline quality.
A new optical temperature measurement technique for semiconductor substrates in molecular beam epitaxy
Authors: Weilmeier M. K. , Colbow K. M. , Tiedje T. , Buuren T. Van , Xu Li
Published: April 2011

A new optical temperature measurement technique for use in molecular beam epitaxy is demonstrated with GaAs substrates. The temperature of the semiconductor is inferred from its band gap, which is measured by the diffuse reflectivity of the substrate that is textured on the back surface. The method has a sensitivity of better than 2 °C, and an absolute accuracy limited by the accuracy with which the band gap is known as a function of temperature. It was found to be necessary to calibrate the measurement technique with a thermocouple in contact with the sample in order to achieve satisfactory accuracy at high temperatures. Measurements of the optical absorption edge of GaAs, show that the slope of the Urbach edge is independent of temperature from room temperature to 450 °C.
Infrared emission from strained-Si1−xGex quantum wells
Authors: Rowell N. L. , Noël J.-P. , Houghton D. C.
Published: April 2011

Photoluminescence was observed for molecular beam epitaxy (MBE) grown Si1−xGex layers with 0.06 < x < 0.60. The spectrum was generally dominated by a ~80 meV wide peak centered ~120 meV below the strained Si1−xGex-alloy band gap, a peak which shifted consistently with Ge concentration. Electroluminescence with a peak energy of 860 meV was observed from a SiGe pin heterostructure grown by MBE and fabricated into mesa diodes. The electroluminescence persisted to temperatures up to 80 K with the diode forward biased at current densities as large as 50 A cm−2. Comparisons are made with the photoluminescence spectra of the same material and an estimate of quantum efficiency is given. A luminescence mechanism involving bound-exciton annihilation without phonon assistance is discussed.
Modelling of semiconductor rib wave guides by a finite difference method
Authors: Delâge A.
Published: April 2011

The method of finite differences is used to solve the scalar wave equation for semiconductor rib wave guides. Boundary conditions derived from continuity relations are applied between regions of different refractive index, allowing more accurate evaluation of the propagation constants for ideal cases of abrupt change in the index. Also appropriate external boundary conditions alleviate the inaccuracy generally introduced by setting the field equal to zero on the external limit of the mesh. Our results agree with various other techniques when applied to typical guiding structures. As an example, we model a multiple-quantum-well structure by using an equivalent layered structure. Mode characteristics and confinement factors obtained by the method are of interest in understanding the behaviour of the lasers and modulators fabricated in our laboratory.
Caractérisation des dispositifs photovoltaïques au a-Si:H
Authors: Diawara Y. , Currie J. F. , Najafi S. I. , Brebner J. L. , Cochrane R. W. , Gujrathi S. C.
Published: April 2011

not available
Color-filter arrays for silicon solid-state image arrays sensors
Authors: Hood Sheldon J. , Chamberlain Savvas G.
Published: April 2011

A monolithic fabrication process for color-filter arrays was developed. The color-filter arrays were composed of a blue, green, and red colored mosaic of transparent film elements. The color-filter arrays were fabricated on silicon wafers on which linear arrays of silicon photodiodes had previously been fabricated. Different colored film elements overlaid different photodiodes so that the spectral response of any photodiode was the produce of its intrinsic response and the transmittance characteristic of the color filter. This technology is applicable to the development of color image sensor arrays. The color-filter arrays utilized a transparent, organic polymer film base as a support for dyes. Organic solvent dyes were chosen to impart color into the film material. Solvent spin-casting techniques were used to coat silicon wafers with polymer films of different colors. The polymer films were patterned by selectively etching the films in an oxygen plasma through an aluminum mask. Measurements were performed on the color-filter-covered photodiodes to determine their spectral response as a function of the wavelength of the incident light. The measurements showed that the color-filter arrays had good color spectral characteristics.
Magnetometer and radar observations of magnetohydrodynamic cavity modes in the Earth's magnetosphere
Authors: Samson J. C. , Greenwald R. A. , Ruohoniemi J. M. , Hughes T. J. , Wallis D. D.
Published: April 2011

Night and early morning data from the Johns Hopkins University, Applied Physics Laboratory HF radar at Goose Bay and from the magnetometers in the Canadian CANOPUS array often show structured spectra with distinct spectral peaks at 1.3, 1.9, and 2.6 mHz. These frequencies are very stable and vary by less than ±5% for the 6 days of data we have analysed. The radar measurements of the F-region drift velocities indicate that these spectral peaks are often associated with field line resonances of the shear Alfvén wave, and that the resonances are seen at lower latitudes as the frequency increases. The magnetometer data indicate that the magnetohydrodynamic (MHD) waves have westward phase velocities. We shall show that these observations are compatible with the formation of MHD cavity modes in the early morning and nightside magnetosphere, between the magnetopause, at approximately 14.5 RE, and turning points in the dipolar magnetosphere, outside the plasmasphere. Likely sources of energy are compressional pulses from the solar wind or Kelvin–Helmholtz instabilities in the low-latitude boundary layer.
Changes in the cosmic-ray power spectrum during solar flares
Authors: Kudela K. , Ananth A. G. , Venkatesan D.
Published: April 2011

The power spectrum analyses of cosmic-ray neutron-monitor data at two different cutoff rigidity stations, Calgary (1.09 GV) and Lomnicky Stit (4.0 GV), exhibit similar changes in power spectral form in the frequency interval 10−5–10−3 Hz before and after the six solar flare events that occurred from January 1989 to June 1990. The power spectrum index n at both stations, which showed significantly lower values one day before the flare onset, indicated a sharp steepening of the spectral shape following the flare event. The change in the power spectrum is attributed to the redistribution of inhomogeneities near the sun, produced before the solar flares in which cosmic-ray particles are accelerated to high energies, to produce a ground level event.
A high-energy increase in cosmic-ray intensity
Authors: Venkatesan D. , Ananth A. G.
Published: April 2011

The increase in cosmic rays observed by neutron monitors with high-energy cutoff, on April 29, 1973, is interpreted to be a definite high-energy phenomenon. This is not associated with any solar flare or interplanetary disturbance. The association of the increase in intensity with geomagnetic index Dst variation indicates a possibility that the high-energy event was caused by a magnetospheric phenomenon.
The ultraviolet imager experiment on the Swedish Viking satellite: Contributions to auroral physics
Authors: Cogger L. L. , Murphree J. S. , Elphinstone R. D. , Hearn D. J. , King R. A.
Published: April 2011

The ultraviolet imager on board the Swedish Viking satellite was designed to provide real-time monitoring of the auroral distribution from space. This objective was achieved over the nominal lifetime of the satellite, March–December, 1986 during which period approximately 45 000 auroral images were acquired. A number of technical and operational innovations have resulted in a rich data base for studies of auroral and magnetospheric processes. Some of the significant scientific advances that have resulted from the investigation of the temporal and spatial development of the auroral distribution include observations of rapid changes of dayside aurora, the effects of this distribution due to the interplanetary magnetic field, and more detailed knowledge of the substorm process. The utilization of models of the Earth's magnetic field to map auroral signatures to the corresponding magnetospheric regions has led to an increased understanding of the mechanisms associated with the large-scale auroral distribution.
Polar airglow and aurora
Authors: McEwen D. J. , Harrington D. A.
Published: April 2011

A survey of night airglow emissions in the polar cap shows stable emission intensities during quiet periods through the winter solstice. Those affected by particle precipitation, OI λ5577 and λ6300, show great variability with solar activity and the state of the interplanetary magnetic field. A statistical study of electron-precipitation occurrence above 78° geomagnetic latitude shows events sufficient to result in observable enhancements in OI emission intensities in about 40% of the satellite passes in the magnetic latitude range from 79° to 83° and in about 15% of the passes for latitudes above 85°. This study provides the necessary background for dynamical studies of polar processes in the planned Canadian polar observatory.
Monte-Carlo simulation of single-line resonance scattering in a rarefied gas
Authors: Lockerbie I. D. , Brooks W. S. C. , How P. , Llewellyn E. J.
Published: April 2011

A Monte-Carlo simulation of single-line resonant scattering in a rarefied gas is presented and the technique is applied to the interpretation of a rocket-borne resonance-lamp experiment. The simulation examines the case of an emitting and absorbing gas at the same temperature for a number of detector and source configurations. The distance from the last scatter point, the angular distribution of the detected scattered photons, and the line shape formed by the scattered photons, at the detector, are evaluated for these different configurations. The simulation results suggest that the scattering of the detected photon occurs very near to the rocket, and not necessarily in the traditional scattering region at the intersection of the detector and emitter normals. It is observed that multiple scattering plays an important role in the number of photons detected and that the apparent gas temperature, as exhibited by the line shapes of the scattered photons, is dependent upon the configuration of the experiment. The simulation results suggest that, for a resonance-scattering experiment to measure constituent concentrations, the experimental design must optimize the return signal and minimize the effect of multiple scattering. The results also suggest that the calibration procedures for resonance-scattering experiments must be made with a physical configuration and environment that is identical to that expected in the rocket flight.
Dislocation detection using polarization-resolved photoluminescence
Authors: Colbourne Paul D. , Cassidy Daniel T.
Published: April 2011

Polarization-resolved photoluminescence is a technique that is capable of accurately measuring mechanical stress in luminescent III–V semiconductors. In this paper, the use of polarization-resolved photoluminescence for the detection and characterization of dislocations from the observed patterns of surface stresses is discussed. Formulae are presented for the calculation of the surface stresses owing to several types of threading and misfit dislocations, and calculated distributions of the expected degree of polarization are illustrated. Examples are given of measured distributions of the degree of polarization, showing excellent agreement with the calculated distributions.
Silicon carbide emitter diodes by LPCVD (low-pressure chemical vapour deposition) using di-tert-butylsilane
Authors: Hewitt S. B. , Tay S.-P. , Tarr N. G. , Boothroyd A. R.
Published: April 2011

Stoichiometric SiC films formed by low-pressure chemical vapour deposition from a di-tert-butylsilane source with in situ phosphorus doping from tert-butylphosphine were used as emitters in heterojunction diodes fabricated on lightly doped silicon substrates. Diode characteristics are nearly ideal, with forward current dominated by injection-diffusion in the silicon substrate.
Characteristics of mesa- and LOCOS-isolated molecular beam epitaxy SiGe diodes
Authors: Tang Z. R. , Salama C. A. T. , Noel J. -P. , Houghton D. C. , Buchanan M.
Published: April 2011

Molecular beam epitaxy grown p+–n SiGe–Si heterojunction diodes with and without p+Si caps on top of the p+ SiGe have been fabricated on n-type Si<100> wafers with and without SiO2 LOCOS patterns. It is shown that the p+Si caps create p+–p+ Si–SiGe isotype heterojunctions in series with the p+–n SiGe–Si heterojunctions. Potential barriers and carrier depletion regions exist in the isotype heterojunction regions owing to the band-gap difference between the two materials. Effects of the LOCOS and the p+–p+ Si–SiGe isotype heterojunction in series with the p+–n SiGe–Si heterojunction on the characteristics of the diodes were studied experimentally and using simulation. The diodes fabricated exhibited I–V characteristics ideality factors between 1.05 and 1.20.
Quantum interference effects as a tool to probe the sidewalls of sub-micrometre-size n+GaAs channels
Authors: Taylor R. P. , Main P. C. , Eaves L. , Thoms S. , Beaumont S. P. , Wilkinson C. D. W.
Published: April 2011

In narrow channels the properties of the sidewalls can have a crucial effect on both the physics and any device functionality of the electronic transport through these structures. We assess the use of electron beam and "dry etching" fabrication techniques to define sidewalls by studying the influence of the sidewalls on the quantum transmission through the channels and, in particular, show the sidewall scattering to be inelastic in nature and to have implications ranging from electron heating to electron coherence effects.
Excess currents as a result of trap-assisted tunneling in double barrier resonant tunneling diodes
Authors: Ma C. L. F. , Deen M. J. , Hardy R. H. S.
Published: April 2011

In this paper, we propose trap-assisted tunneling (TAT) to account for the discrepancy between theoretical predictions and measured valley currents (also called excess currents) in double barrier resonant tunneling diodes (DB RTDs) with observed generation–recombination noise spectra. This proposed mechanism in DB RTDs is required, since predictions of excess currents from the models involving no gap states, such as quantum coherent tunneling, are too low. The model is also supported by the observed strong correlation between excess current and low frequency noise spectra. The trap states are assumed to be at or near the interface between the emitter and the first barrier in DB structures. The electrons trapped in the trap states emit out to tunnel through the double barriers. The empty trap states are then refilled by the electrons from the conduction band of the emitter. The conservation of the energy and momentum are incorporated through the emission–absorption of phonons. Based on these mechanisms, we propose a semiempirical formula for calculating valley current with three parameters, which are related to some physical parameters. A simple semiphysical model is set up to justify the three parameters and the detailed derivation is given. This two-step TAT currents are calculated for our examples of AlAs–GaAs–AlAs DB RTDs and are found to be in agreement with the measured excess currents. The variation of excess currents with temperature is also discussed. Improvement of the peak-to-valley current ratio, among other device design and fabrication considerations, depends on the reduction of these trap states.
Fabrication of novel self-aligned metal insulator semiconductor field effect transistors (MISFETs) on InP by a S interface engineering technique
Authors: Sundararaman Chetlur S. , Currie John F.
Published: April 2011

In this paper we demonstrate for the first time that self-aligned metal insulator semiconductor field effect transistors (MISFETs) can be realized on InP by incorporating an effective surface passivation technique in the fabrication process. A chemical sulfur treatment is used to passivate the InP – indirect plasma silicon nitride interface that results in interface state densities (Dit) in the low 1011/cm2 eV. It is observed that while passivated self-aligned MISFETs subjected to post-passivation high-temperature process cycles up to 700 °C exhibit acceptable transistor characteristics, unpassivated MISFETs using the same process do not show any transistor action. The passivation procedure has been successfully used to demonstrate for the first time a self-aligned InP–InGaAs–InP heterojunction insulated gate FET. We conclude from this work that interface engineering techniques like the one used in this study would be essential to realize and (or) improve the performance of self-aligned FET structures based on InP. The fabrication process described here can be directly applied to similar interface engineering techniques.
Electronic properties of (NH4)2S passivated InP(100) surfaces
Authors: Tao Y. , Yelon A. , Leonelli R.
Published: April 2011

We have recently presented a method that yields chemically and thermally stable S-passivated InP(100) – (1 × 1) surfaces. Here we characterize the surface electronic properties using two techniques: band edge and exciton photoluminescence intensity and Schottky diode current–voltage characteristic measurements. We compare etched and S-treated samples, both in the as-prepared condition and after annealing. These measurements show that the S-treated surfaces have better properties than the etched ones. In particular, photoluminescence intensities are improved by a factor of two to four.