bluuebunny/crossref_metadata_2025 huggingface dataset:
Model of low-frequency noise and oscillations in GaAs metal-semiconductor-field effect transistors (MESFETs)
Authors: McAlister S. P. , Li Z.-M. , Day D. J.
Published: April 2011

We examine the theoretical and experimental aspects of low-frequency noise and oscillations in GaAs metal-semiconductor-field-effect transistors. We attribute the f−3/2 noise behaviour that is often observed in these devices to trap-modified diffusion in the semi-insulating substrate and review the derivation of analytical formulas for the spectrum. The low-frequency oscillations are correlated with the noise and we discuss the contribution to the noise from the random generation of slow domains in the substrate. We derive formulas to describe these oscillations in the drain current. Calculations using our model successfully imitate the experimental results for the noise and oscillations.
Thermal modeling of CMOS (complementary metal-oxide semiconductor) temperature and (or) flow microsensors
Authors: Chau Kris , Allegretto Walter , Ristic Ljubiśa
Published: April 2011

In the past few years, it has become possible to construct CMOS (complementary metal-oxide semiconductor) microstructures suitable for temperature and (or) flow sensing applications. We present numerical modeling results for such structures, and discuss the effect several parameters have on the performance of such sensors.
Two-phase GaAs cermet-gate charge-coupled devices
Authors: LeNoble M. , Cresswell J. V. , Johnson R. R.
Published: April 2011

A nonplanar 64-pixel, 2-phase GaAs cermet-gate charge-coupled device (CMCCD) and a planar 128-pixel, 2-phase GaAs CMCCD are described. The former device employs a castellation to provide the "built-in" electric field for controlling the flow of signal charge within the channel, whereas, the latter device uses externally applied electric fields to achieve this control. Both devices have been operated at 46 MHz, demonstrating charge transfer efficiencies of 0.996 and in excess of 0.999, respectively. The application of the planar 2-phase GaAs CMCCD in a 500 or 7.81 MHz transient digitizer module for acquisition and transfer of dc to 250 MHz band-limited signals will also be presented.
Electrical transport properties of CdSe thin-film transistors with Cr contacts
Authors: Waechter David , Leith Graham , Zukotynski Stefan
Published: April 2011

Electrical transport properties of CdSe thin-film transistors have been examined as a function of lateral distance from Cr contacts. The results show that the channel conductivity is enhanced in the vicinity of the contacts and drops sharply at a critical distance. The magnitude of this distance is sensitive to the surface treatment prior to CdSe deposition. Hall-effect measurements show an increasing electron mobility with increasing gate voltage, consistent with gate-voltage-induced lowering of grain-boundary potential barriers.
Characterization of ultrathin Ge epilayers on (100) Si
Authors: Baribeau J. -M. , Lockwood D. J. , Jackman T. E. , Aebi P. , Tyliszczak T. , Hitchcock A. P.
Published: April 2011

The understanding of the epitaxy of pure Ge layers on Si is an important step towards the synthesis of SimGen (m, n < 10 monolayers) short-period superlattices. The possibility of a direct band-gap character makes these structures extremely attractive. We have grown thin buried Gen ([Formula: see text] monolayers) films on (100) Si by molecular beam epitaxy and studied their structural properties by a variety of techniques including Raman scattering spectroscopy, glancing incidence X-ray reflection, Rutherford backscattering, transmission electron microscopy, and extended X-ray absorption fine structure analysis. All these techniques allowed detection of the thin Ge layers and provided information about the thickness, morphology, strain distribution, and interface sharpness of these heterostructures. The Ge„ films with [Formula: see text] had a two-dimensional nature and showed no sign of strain relaxation. Intermixing at the Si–Ge interfaces was present in all these films and estimated to be not more than two monolayers. This smearing at the interfaces may have contributed to the maintenance of that pseudomorphicity. A thicker Ge layer (n = 12) showed evidence of strain relaxation and clustering in three-dimensional islands.
Raman spectroscopy of PLEE (pulsed laser evaporation and epitaxy)-grown Cd1−xMnxTe films on (111) GaAs and (001) InSb
Authors: Keeler W. J. , Dubowski J. J.
Published: April 2011

Raman light-scattering measurements have been used to characterize Cd1−xMnxTe (CMT) epilayers, 0.6–1.7 μm thick, deposited using pulsed laser evaporation and epitaxy (PLEE) on (111) GaAs and (001) InSb. Under outgoing resonance Raman conditions with a photoluminescence peak thought to be due to neutral acceptor-bound magnetic polaron emissions, five to seven overtones in various combinations of the "CdTe–like" and "MnTe–like" longitudinal optic phonon modes have been seen in six samples of CMT–GaAs at 14 K. This extreme degree of enhancement attests to the high quality of the PLEE-grown epilayers. The combination of the II–VI semiconductor CdTe and the III–V substrate InSb in a heterojunction is of particular interest because of the nearly perfect lattice match (within 0.05% at 300 K) and the large difference in the band gaps (1.45 and 0. 18 eV), which promise interesting device applications. Measurements of Raman scattering for CdTe deposited on n- and p-type (001) InSb were performed. Films with an intermediate CdTe buffer layer show better Raman characteristics than those produced without the buffer layer or with a Cd overpressure.
The effect of main-ion-beam parameters on some properties of a-Si:H prepared by ion-beam-assisted reactive evaporation
Authors: Zhang S. , Brodie D. E. , Audas R. D.
Published: April 2011

This paper reports the effect of the ion-beam-source parameters on the properties of a-Si:H deposited by ion-beam-assisted reactive evaporation with silane as the feedthrough gas. It is observed that the hydrogen concentration (CH) in the resulting film is determined mainly by the ion-beam intensity at the substrate for a fixed substrate temperature (about 60 °C), a fixed silane partial pressure (2 × 10−4 Torr (1 Torr = 133.3 Pa)) and a fixed deposition rate (8 nm min−1). As CH increases from 15 to 34 at.% in films containing 3 at.% carbon, the SiH stretching mode in the IR absorption spectrum shifts from 2000 to 2055 cm−1. The ratio of the photoconductivity to dark conductivity depends not only on the incident ion density (or CH), but also on the ion-beam energy. Near an ion energy of 200 eV and a CH of 24 at.%, this ratio goes through a maximum (~1 × 105). Electron-diffraction patterns show that the films are amorphous, and microscopic observations by transmission electron microscopy illustrate that when suitable ion-beam parameters are used, the porosity of the films is reduced.
Epitaxy of Cd0.90Mn0.10Te for optoelectronic devices
Authors: Dubowski J. J. , Thompson J. R. , Benzaquen R. , Roth A. P. , Wasilewski Z.
Published: April 2011

We report on pulsed laser evaporation and epitaxy (PLEE) of Cd0.90Mn0.10Te material that has potentials for application in optoelectronic devices operating in the wavelength range of 750–850 nm. Two lasers, Nd:YAG and excimer XeCl, are used to provide fluxes of atoms by laser ablation of high-purity polycrystalline targets. We demonstrate that the XeCl-laser-induced congruent vaporization of a multi-element solid target led to epitaxy of Cd0.90Mn0.10Te. The epitaxial layers were grown on (001) InSb and (001) Cd0.955Zn0.045Te substrates held at a temperature in the range of 200–240 °C. Structural characterization of the layers was carried out with in situ reflection high-energy electron diffraction, scanning electron microscopy, and double crystal X-ray diffraction. An excellent reproducibility of chemical composition of the PLEE-grown films has been demonstrated. Optical and structural properties of the films correspond to those of the best bulk Cd0.90Mn0.10Te or epitaxial layers grown by molecular beam epitaxy or metal organic vapour phase epitaxy.
Electrical characterization of CdTe–InSb heterojunctions
Authors: Thompson J. R. , Dubowski J. J. , Northcott D. J.
Published: April 2011

Planar and vertical transport studies were carried out on samples of epitaxial (001) CdTe grown by pulsed laser evaporation and epitaxy on n- and p-type (001) InSb substrates. Characterization was performed in the temperature range of 4.2–300 K, including Hall effect, current–voltage, and capacitance–voltage measurements. Ohmic contacts to intrinsic CdTe were obtained by application of a AuCl3, aqueous solution. Similar contacts on grown layers showed no Schottky-barrier characteristics. Layers on n-type substrates did not exhibit rectification. Hall effect and resistivity measurements using contacts to the epilayer are in agreement with bulk n-InSb for the range 120–300 K. Below 120 K current dependence in the measured resistivity is observed with a saturation value at low currents, indicating confinement of the transport to the epilayer. CdTe–p-InSb junctions exhibit rectification characteristics below 80 K with C–V measurements yielding a barrier height of 0.17 V. Hall measurements with contacts to the epilayer showed erratic Hall-voltage measurements, but substrate contacts indicate conduction through InSb implying a depleted layer. Estimated electron concentration and mobility in the CdTe layer are n > 8 × 1016 cm−3, and u ~ 104 cm2 V−1 s−1.This indicates that n-type doping of the CdTe layers, possibly due to the incorporation of In, may take place even at the lowest growth temperature.
Charge decay in amorphous selenium layers with an intermediate aluminum oxide film
Authors: Zhang Qi-Hua , Champness C. H.
Published: April 2011

Amorphous selenium is often used as the basic photoreceptor material in xerography in the form of a layer on an aluminum substrate. It is found that the dark decay rate of charge on the selenium surface can be reduced by the presence of a thin aluminum oxide film between the selenium and the substrate metal. In this study, different methods were explored for forming this film, including direct thermal oxidation and various glow-discharge methods. It was found that with thermal oxidation and low voltage glow discharge, the film thicknesses were limited to about 200 Å (1 Å = 10−10 m). However, with dc reactive sputtering, aluminum oxide films with thicknesses of more than 2000 Å could be prepared. Evaluation of the films, with the selenium layer present, indicated that the low voltage glow-discharge and direct thermal oxidation methods gave the best results xerographically.
What is the atomic structure at solid-state interfaces?
Authors: Kavanagh Karen L. , Chang Jessica C. P. , Sullivan Patrick
Published: April 2011

Significant progress has been made towards our understanding of Schottky barriers, ohmic contacts to GaAs, and misfit dislocation generation at heteroepitaxial interfaces. These subjects are briefly reviewed in this paper. However, many of the remaining issues still hinge on a more detailed knowledge of the atomic structure at interfaces and its effect on electron transport. A new technique, ideal for this problem, entitled ballistic electron emission microscopy (BEEM) is described. In BEEM the spatial resolution of the scanning tunneling microscope is used to probe the local current transport at an interface.
Analytical microscopy of titanium nitride
Authors: Simard-Normandin M. , Weaver L. , Vacca D. , Rogers D. , Vitkin A. , Tiedje T.
Published: April 2011

We report on microscopy tools for the in-situ analysis of TiN in microelectronic devices. Scanning tunnelling microscopy and Raman microprobe spectroscopy are compared with scanning and transmission electron microscopy.
Quantitative photopyroelectric out-of-phase spectroscopy of amorphous silicon thin films deposited on crystalline silicon
Authors: Christofides Constantinos , Mandelis Andreas , Engel Albert , Bisson Michel , Harling Gord
Published: April 2011

A photopyroelectric spectrometer with real-time and(or) self-normalization capability was used for both conventional transmission and thermal-wave spectroscopic measurements of amorphous Si thin films, deposited on crystalline Si substrates. Optical-absorption-coefficient spectra were obtained from these measurements and the superior dynamic range of the out-of-phase (quadrature) photopyroelectric signal was established as the preferred measurement method, owing to its zero-background compensation capability. An extension of a photopyroelectric theoretical model was established and successfully tested in the determination of the optical absorption coefficient and the thermal diffusivity of the sample under investigation. Instrumental sensitivity limits of βt ≈ 5 × 10−3 were demonstrated.
Effects of neutron and electron irradiation on the absorption edge of GaAs
Authors: Parenteau M. , Carlone C. , Aubin M. , Khanna S. M. , Anderson W. T. , Gerdes Jr. J. W.
Published: April 2011

Semi-insulating liquid encapsulated Czochralski GaAs wafers were submitted to irradiation with 1 MeV neutrons, thermal neutrons, 7 MeV electrons, and white electrons (up to 7 MeV). The direct absorption edge was then studied by means of transmission (T = 15 K) and thermoreflectance (T = 35 and 51 K) measurements. Thermoreflectance spectra showed that the position of the exciton does not shift after irradiation with 1 MeV neutrons, but that its broadening parameter Γ increases as the fluence increases. Transmission measurements have revealed the presence of two acceptor levels (C and Zn) in the unirradiated samples. The absorption associated with these impurities increased by a factor of 10 after irradiation with 1 MeV neutrons. This effect was not produced by the three other types of radiation. However, an absorption tail extending well below the direct edge is seen after irradiation with all four types of particles. A model proposed by Toyozawa fits this continuum quite well, suggesting that irradiation causes amorphization of the crystal. The rate of introduction of defects and its dependence on irradiation fluence is different for each type of radiation.
The sulfur-passivated InP surface
Authors: Sundararaman C. S. , Poulin S. , Currie J. F. , Leonelli R.
Published: April 2011

The passivation of the InP surface by sulfur treatment is studied in the temperature range between 150–300 °C by angle resolved X-ray photoelectron spectroscopy and photoluminescence measurements. The thermal sulfurization results in a 30 Å (1 Å = 10−10 m) overlayer of In2S3 and P2O5. This cap layer lowers the phosphorus escape rate from the substrate thereby reducing the defects associated with phosphorus vacancies.
Sequential optical study of the component layers of a semiconductor quantum-well system
Authors: Fafard S. , Fortin E. , Roth A. P.
Published: April 2011

The constituent layers of an InGaAs–GaAs single quantum well were studied systematically and sequentially using photoluminescence, photovoltaic, and electroluminescence techniques. Spectra were obtained first on the base of the device, a heavily silicon-doped GaAs substrate, then on the substrate plus the undoped-GaAs buffer layer, and finally on the complete device consisting of the substrate, buffer layer, single metal-organic vapour phase expitaxially grown In0.13Ga0.87As quantum well (width 5.0 nm), and a GaAs cap layer. Such separate optical spectra may be required to assess the origin of spectral features when the energy of quantum-well transitions are coincident with the energies of possible transitions in the cladding layers. The results showed that when for instance, experimental conditions permit the excitation of the substrate, peaks of substrate origin whose amplitude is comparable with that of the fundamental peak of quantum-well origin (11H) could be observed. In photoluminescence, long-wavelength excitation or a thin buffer layer may enhance emission from the underlying substrate. The nature of the contact used in the electroluminescence and photovoltaic effects may also influence the relative response of the component layers. Finally, a convenient method is developed to calculate the energies of the levels in a single quantum well, as functions of the well width, for a given alloy composition and temperature.
Carrier loss by rapid thermal-annealing in Si-doped GaAs grown by MOCVD (metal-organic chemical vapour deposition)
Authors: Aktik C. , Currie J. F. , Bosse F. , Cochrane R. W. , Auclair J.
Published: April 2011

Si-doped GaAs epitaxial layers grown by metal-organic chemical vapour deposition exhibit substantial carrier density loss after rapid thermal annealing (RTA) at temperatures higher than 850 °C. Hall-effect, capacitance–voltage, deep-level transient spectroscopy, and secondary ion mass spectroscopy measurements were performed on samples before and after RTA. We show that the reduction of free-carrier concentration in the entire thickness of the epitaxial layer is accompanied by the deterioration of the mobility and the enhancement of donor-like deep-level concentration at 0.305 eV below the conduction band, which is in good agreement with the model of silicon donor neutralization by formation of neutral silicon–hydrogen complexes.
Epitaxy of III–V semiconductors
Authors: Balk P. , Brauers A. , Grützmacher D. , Kayser O. , Weyers M.
Published: April 2011

This paper is concerned with the control of the epitaxial deposition of III–V materials by means of techniques using metal organic group III compounds and group V hydrides as starting materials: metal-organic vapour-phase epitaxy and metal-organic molecular-beam epitaxy. Such control is essential with regards to intentional and background doping and for the sake of the uniformity of the film properties of binary semiconductors. In systems containing ternary and quaternary materials, there is the further requirement of compositional control and lattice matching. In addition to the equipment aspects, this paper will discuss the contributions to be expected of novel precursors and the control problem related to selective area growth. Finally, the growth of multiple quantum well structures will be reviewed as a test case for mastering epitaxial deposition.
Channeling and photoluminescence measurements of heteroepitaxial layers of InxGa1−xAs
Authors: Hetherington D. W. , Hinrichsen P. F. , Masut R. A. , Morris D. , Roth A. P.
Published: April 2011

The crystalline quality and tetragonal strain of heteroepitaxial InxGa1−xAs (x = 0.12) on GaAs substrates have been measured as a function of layer thickness by Rutherford back-scattering channeling with 2.5 MeV alpha particles. The strain in each layer was measured by finding the angular displacement between the <112> axial channels of the epilayer and the substrate. The layers were grown by low-pressure metal-organic vapour phase epitaxy on GaAs substrates with surfaces oriented (i) exactly on a (100) plane and (ii) misoriented by 2° from the (100) plane towards the <110> axis. Layers of thickness well below the critical value exhibit remarkably low χmin values, indicating that their crystalline quality is close to perfect. The channeled spectra of layers that exceed the critical thickness clearly demonstrate the existence of misfit dislocations concentrated at the interface. The channeling results are correlated with photoluminescence measurements on the same samples. The two techniques give different results for the strain in the samples. The discrepancy is probably due to the different sensitivities of the two techniques to the local strain in the samples.
Effet des paramètres de croissance sur les couches épitaxiales d'InP obtenues par MOCVD (metal-organic chemical vapor deposition) à basse pression
Authors: Cova P. , Masut R. A. , Currie J. F. , Bensaada A. , Leonelli R. , Tran C. Anh
Published: April 2011

The development of a low pressure, horizontal MOCVD (metal-organic chemical vapour deposition) reactor has allowed us to study the effect of phosphine and trimethylindium molar fluxes on the epitaxial growth of InP. Study of the growth rate in the temperature range 550–620 °C shows that the growth can be limited by the reaction kinetics at the surface. Epitaxial layers of good morphological quality have been obtained by reducing the rate of growth even if the growth is limited by the reaction kinetics at the surface. The variation of the electronic mobility with the PH3 molar flux reveals the existence of an optimum mobility region, even with a constant V: III ratio. Photoluminescence experiments carried out on the samples show the good crystallographic quality of the epitaxial layers. Spectra taken in the energy range 0.8–1.2 eV show the evolution of two structures at 0.91 and 1.08 eV that we associate with an antisite PIn and a VIn defect, respectively.[Journal translation]
Donor identification in bulk GaAs by Fourier transform photoluminescence
Authors: Beckett D. J. S. , Nissen M. K. , Thewalt M. L. W.
Published: April 2011

The identification of substitutional shallow donors in GaAs by optical techniques has been problematic because of the extremely small chemical shifts of these effective-masslike impurities. Photoluminescence has been successfully applied in identifying donors in high-purity epitaxial material through the painstaking use of high-resolution spectroscopy, high-magnetic fields, and resonant excitation. Relatively little work has been done in bulk GaAs, where the broadened transitions hinder the resolution of different species. Recently we demonstrated that the high resolution and high-signal throughput obtained with Fourier transform photoluminescence (FTPL) gives superior results for epitaxial material. In this report we show that the advantages of FTPL can also be applied to reliable donor identification in bulk GaAs.
Prospects of quantum functional devices
Authors: Ismail K.
Published: April 2011

In this paper, the present status of devices, which operate on the basis of quantum mechanical concepts is reviewed and their potential applications are analysed. The analysis comprises the design aspects and a comparison between planar and vertical structures. The planar devices are emphasized in particular and the relevant fabrication techniques and material requirements are discussed. Potential future applications are investigated.
Stress optimization in SiC films for X-ray-mask membrane application
Authors: Boily S. , Chaker M. , Ginovker A. , Mercier P. P. , Pépin H. , Kieffer J. C. , Currie J. F. , Lafontaine H.
Published: April 2011

One of the key factors for successful X-ray lithography is a well-established and controlled X-ray-mask technology. In this paper, we describe the development of a silicon carbide membrane for X-ray-mask applications. The most critical step is the generation of thin SiC films (~2 μm of thickness) with a low tensile stress (< 1 × 109 dynes cm−2 or 1 × 108 Pa). For this purpose, the SiC films were prepared in a 100 kHz plasma-enhanced chemical vapor deposition system from a gas mixture of silane, methane, and argon on a Si substrate. The appropriate low tensile stress is then achieved by thermal annealing. Using this method, SiC membranes of 2.5 cm diameter were obtained.
Magneto-optical study of Ga0.47In0.53As–InP under hydrostatic pressure
Authors: Beerens J. , Bernier G. , Lasserre S. , Pelenc D. , Puetz N. , Miner C. J.
Published: April 2011

Far-infrared and interband photoconductivity measurements were carried out on high-purity Ga0.47In0.53As. All the measurements were performed at 4.2 K or below in magnetic fields up to 16 T. Hydrostatic pressure of up to 10 kbar (1 bar = 105 Pa) was also applied on the sample during the experiments, using the liquid clamp cell technique. Our work was mainly focussed on the study of conduction-band nonparabolicity. The dependence of the electron effective mass toward energy was accurately determined from our cyclotron resonance measurements and compared with a theoretical description that includes nonparabolicity and magnetopolaron effects. We find that the nonparabolicity coefficient and its variation with pressure are in agreement with the theoretical predictions based on the Kane model, when the contribution of magnetopolaron effect is included in the data analysis. These results are correlated with those obtained in the interband measurements, which have been analysed within a Pidgeon–Brown approach. Some interesting data concerning impurity states were also obtained in our far-infrared photoconductivity measurements. A much richer set of Zeeman-split impurity-related peaks were recorded, as compared with previously published results. The influence of pressure, nonparabolicity, and the magnetopolaron effect on the position of these peaks will be briefly discussed.
The quantum-confined Stark effect in shallow quantum wells
Authors: Gibb K. , Lacelle C. , Sun Q. , Fortin E. , Roth A. P.
Published: April 2011

We have investigated the quantum-confined Stark effect for a series of four InGaAs–GaAs single quantum wells using photocurrent spectroscopy. All four samples reveal quadratic Stark shifts for the lowest electron-to-heavy-hole transition at weak electric fields. The field dependence becomes subquadratic at large applied fields. The field dependent reduction of the exciton binding energy is measured and is on the order of a millielectron volt for applied electric fields approaching 80 kV cm−1.
Ajustement par recuits rapides RTA (rapid thermal annealing) des contraintes dans des couches minces de tungstène utilisées comme absorbant pour des masques à rayons X
Authors: Lafontaine H. , Currie J. F. , Boily S. , Chaker M. , Pépin H.
Published: April 2011

Tungsten thin films are deposited with a triode sputtering system in order to obtain an absorbing layer for X-ray masks. The mechanical stress is studied as a function of different pressure and RF power conditions during deposition. Rapid thermal annealing at different temperatures and durations is performed in order to produce films under low compressive stress. We observe that the stress changes occur over the time scale of seconds at the annealing temperature and that the corresponding activation energies are low (60 meV). Grain growth in a preferred orientation explains the observed changes in stress. The magnitude in the change of stress is in good agreement with a model proposed by Hoffman et al. relating the stress to grain size and grain boundary dimensions. [Journal translation]
Development and characterization of polysilicon emitter solar cells
Authors: Papadopoulos G. , Boivin L. P. , Tarr N. G.
Published: April 2011

Solar cells with emitters consisting of a very thin (<20 nm) layer of silicon deposited in the polycrystalline phase overlaid with a thicker (≈100 nm) layer of recrystallized amorphous material were fabricated and characterized. Both layers were formed by low-pressure chemical vapor deposition with heavy in situ phosphorus doping. The highest temperature used in processing was 650 °C. Short-circuit current densities (Jsc) of 30 mA cm−2 combined with fill factors close to 0.8 were achieved under simulated 100 mW cm−2 AM1.5 illumination. Open-circuit voltages as high as 669 mV at 28 °C were obtained for cells formed on high-quality 0.1 Ω cm float zone substrates when Jsc was set to 32 mA cm−2.
GaAs–AlGaAs multiple-quantum-well lasers for monolithic integration with optical modulators
Authors: Chatenoud F. , Dzurko K. M. , Dion M. , Moss D. , Barber R. , Delâge A. , Landheer D.
Published: April 2011

Calculations of multiple-quantum-well laser threshold current show that a common minimum current value exists for each number of wells, at an appropriate cavity length. This optimum cavity length decreases rapidly with increasing number of wells, for instance from about 300 to 110 μm for one to three wells. Granded-index separate-confinement heterostructure (GRINSCH) lasers with 1–10 quantum wells, grown by molecular beam epitaxy, show consistently low threshold currents that agree well with theoretical predictions. Lasing is achieved at 160 A cm−2 and 4.6 mA for broad-area and ridge waveguide single-quantum-well devices, respectively. The field-dependent electroabsorption of these devices when operating as wave-guide modulators indicates good modulation properties for one and three quantum-well structures, with on:off ratios above 55 at lasing wavelength. The behavior becomes more complex with increasing number of wells. This systematic study of discrete multiple-quantum-well lasers and modulators demonstrates that GRINSCH structures with 1–3 wells are the most suitable for monolithic integration. Design rules for the laser cavity are also presented for numbers of wells ranging from 1 to 10.
Sub-half-micrometre gratings using e-beam lithography and reactive ion etching
Authors: Fallahi M. , Barber R.
Published: April 2011

A simple, manufacturable technique for the generation of sub-half-micrometre gratings in GaAs is demonstrated. The technique uses a single layer of polymethylmethacrylate photoresist, electron-beam lithography, and BCl3–He reactive ion etching to achieve high-quality second-order gratings. Good light attenuation properties are demonstrated for planar and ridge wave guides.
Modeling of ultrafast metal–semiconductor–metal photodetectors
Authors: Landheer D. , Li Z.-M. , McAlister S. P. , Aruliah D. A.
Published: April 2011

We have simulated the transient response of metal–semiconductor–metal (MSM) photodetectors to an optical impulse, using a two-dimensional (2-D) drift-diffusion model that incorporates deep traps and appropriate boundary conditions. We incorporate the external circuit using a method originally developed to describe photoconductors in transmission lines. Initially a one-dimensional (1-D) simulation is used to verify our model comparing our results to previous 1-D calculations and experimental results for GaAs MSM detectors. Then a full 2-D analysis is used to predict the performance of a novel MSM wave-guide photodetector whose structure incorporates a Si–Si0.5Ge0.5 strained-layer superlattice. We show that this device can have a response as fast as 50 ps, although pulse pile-up due to slow diffusion of carriers may be a problem at high duty cycles.
SiO2 spin-on glass deposited on Si, GaAs, and InP
Authors: Shen Pengnian , Iraj S. , Najafi Najafi , Currie John F.
Published: April 2011

We used the spin-on glass solution to fabricate thin transparent SiO2 films on Si, GaAs, and InP. Both pure SiO2, and TiO2-, P2O5-, and In2O3-doped SiO, are fabricated. The normalized reflectance minimum method is used to determine both the film thickness and the refractive index. The refractive index of the film depends on the processing conditions and the dopant concentration. We have measured normalized reflectance and compared it with values calculated for both pure and doped films. The agreement is good. The CF4–O2 sputtering etch rates of the films are investigated as a means to pattern the films to form light-guiding structures.
Minority carrier diffusion length determination from capacitance measurements in Se–CdO photovoltaic cells
Authors: Champness C. H. , Shukri Z. A. , Chan C. H.
Published: April 2011

In Se–CdO photovoltaic cells, the electron diffusion length Ln in the selenium absorber layer has been determined from measurements of capacitance C and photocurrent under monochromatic illumination by variation of applied reverse bias. If penetrating incident light of band-gap wavelength is used, a plot against 1/C of the illuminated-to-dark current change ΔI yields a straight line over a certain range of bias values. Extrapolation of this line to the 1/C axis yields Ln. It was found in the fabrication of the Se–CdO cells that increasing the substrate temperature from 100 to 140 °C during the selenium deposition resulted in an increase in the cell photovoltaic output. Capacitance and ΔI measurements on these cells showed an increase in diffusion length with substrate temperature, indicating that the increased cell performance was due to improved electron collection in the selenium layer.
Inference of magnetospheric and ionospheric electrical properties from the decay of geomagnetic activity
Authors: Rostoker G. , Phan T. D. , Pascal F.
Published: April 2011

The three-dimensional current system characteristic of directly driven magnetospheric substorm activity that couples the magnetosphere to the ionosphere can be represented by an LCR circuit where the source of the emf, the capacitance, and the resistance are in parallel. An earlier study (G. Rostoker and F. Pascal. Can. J. Phys. 68, 74 (1990).) has shown that the impulse response of the magnetosphere can be represented by the response of such an LCR circuit to a sudden increase in the crosstail potential drop ε, where the circuit parameters, (ε, L, C, R) are all permitted to vary with time as the current in the circuit asymptotically approaches its new level. In this paper we examine the response of the directly driven system to sudden northward turnings of the interplanetary magnetic field. We find that the directly driven westward electrojet in the dawn sector decays in an approximately exponential fashion following the northward turning, and that the decay time is nearly linearly dependent on the value of the auroral electrojet (AE) at the time of the northward turning. We use the relationship between the characteristic time constant of the decay and the magnitude of AE at the time of the northward turning to develop quantitative expressions describing the magnitudes of the electrical bulk parameters, L, C, and R as a function of the level of magnetospheric activity.
Ten years of calibration for the ISIS-II red line photometer
Authors: Gertner Bluma S. , Shepherd Gordon G.
Published: April 2011

The York University Red Line Photometer was launched on the ISIS-II spacecraft on April 1, 1971. Its operations for more than a decade were ended not by any physical fault, but by a policy decision to terminate support for ISIS operations. Since ISIS-II was the last of a series of four satellites this effectively concluded Canada's scientific satellite programme. The satellite was then "given" to the Japanese, who continued to operate it to obtain topside sounder data. They did not have the resources needed to operate the other instruments, so no Red Line Photometer data were obtained after that time. It is nevertheless of considerable interest to track the behavior of the optical elements, which had a decade of operation in space. In this paper we present 10 years of calibration of the Red Line Photometer; no degradation of any optical elements can be identified.
Observations of ELF (extremely low frequency) signatures arising from space vehicle disturbances of the ionosphere
Authors: Dea Jack Y. , Bise William Van , Rauscher Elizabeth A. , Boerner Wolfgang-M.
Published: April 2011

We report on observations of extremely low-frequency (ELF) signatures during exit or reentry of space vehicles through the ionosphere. The two modes regularly observed gave signals that peaked at 5.6 and 11.2 Hz. The evidence points to the lower ionosphere, i.e., the D- and E-layers, as the generator of these signals. The measurements were performed using ground-based multiturn coil sensors located in Reno and San Diego. The nature of these signals is unclear at present but it is surmised that we are detecting either the evanescent fields of hydromagnetic waves traveling in the ionosphere or the oscillating geomagnetic field associated with these hydromagnetic waves.
Climatologies of mean winds and tides observed by medium frequency radars at Tromsø (70°N) and Saskatoon (52°N) during 1987–1989
Authors: Manson A. H. , Meek C. E.
Published: April 2011

A real-time winds system from Saskatoon has operated with the Tromsø medium frequency (MF) (partial reflection) radar (70°N, 20°E) since mid-1987. Although the system has a poorer data yield than usual, owing to smaller receiving antennas, it has proven possible over 2 years to obtain 12 month climatologies of mean winds and tides (70–75 to 100 km) with a 10 d resolution. These are compared with similar products from the Saskatoon MF radar (52°N, 107°W). The mean winds and tides generally show similar seasonal morphologies. However the mean winds are weaker, consistent with smaller meridional temperature gradients. Also, there are significant changes in the tidal wavelengths and amplitudes suggesting that considerable adjustments of modal composition have occurred. The tides are compared with recent numerical-theoretical models.
Corotational solar streams and cosmic-ray diurnal anisotropy
Authors: Ananth A. G. , Venkatesan D.
Published: April 2011

A detailed comparison of the behavior of cosmic-ray diurnal anisotropy with the solar activity cycle indicates that the amplitude of the diurnal anisotropy is significantly modulated by the corotational streams that produce the secondary peak in geomagnetic activity. However, the time of the maximum of diurnal anisotropy does not show any systematic changes with solar activity but indicates a shift towards earlier hours (~12:00 LT), corresponding to the reversal of polarity of solar magnetic fields.
The response of the quiet-time auroral configuration to short- and long-term interplanetary magnetic field variations
Authors: Murphree J. S. , Cogger L. L. , Elphinstone R. D. , Hearn D.
Published: April 2011

Observations from the IMP-8 satellite of the interplanetary magnetic field (IMF) are compared with areas of the polar region bounded by the aurora as observed by the Viking spacecraft during quiet-time conditions (IMF Bz northward). A variety of energy-coupling functions are investigated and it is determined that the auroral distribution can be best described by the inclusion of azimuthal terms in addition to standard energy-coupling functions. The auroral distributions for Bz northward support antiparallel merging as a mechanism whereby energy is transferred to the magnetosphere from the solar wind. As well, however, when the polar angle is small the region bounded by the auroras expands and may be controlled more by wave interaction at the magnetopause. Observations by the Viking spacecraft indicate a dominance of dusk sector polar arcs in the spring time and dawn sector arcs in the fall (post equinox). Two alternative mechanisms can explain the observations. One involves the ordering of the IMF in a solar equatorial coordinate system while the other involves the Sun's polarity and the traversal of the Earth's orbit through different heliographic latitudes. A test is proposed whereby the two hypotheses can be investigated during the next solar cycle.
Spatial relationship of visual arcs to auroral electrojets
Authors: Pao Q. , Cogger L. L. , Wallis D. D. , McNamara A. G.
Published: April 2011

Observations of the 5577 Å (1 Å = 10−10 m) emission detected with an all-sky imager are superimposed onto maps of auroral E-region coherent backscatter at 50 MHz made by the bistatic auroral radar system (BARS) to obtain the spatial and temporal relationships of stable visual arcs to auroral electrojets and the Harang discontinuity. At large aspect angles, characteristic of BARS, many eastward electron-drift velocities appear poleward of the visual arcs, in agreement with a recent proposed explanation that is based on refraction through auroral ionization structures in the E region. For some observations, the radar echoes are essentially co-located with the visual aurora. When the Harang discontinuity is present, the discrete arc separates the counterstreaming electron flow. Under these circumstances, the electric field in the E region associated with the stable arc agrees with the theoretical electric-field simulation, in which the electric field with a maximum magnitude of 40 mV m−1, reverses direction across the discrete auroral arc. It is also evident from the observations that there is often no obvious spatial correspondence between the visible aurora and the velocity vectors of the electron flow. In some cases there exists electron flow with a large southward component across the stable arc.
Inferring middle-atmospheric ozone height profiles from ground-based measurements of molecular oxygen emission rates, I: Model description and sensitivity to inputs
Authors: Sica R. J.
Published: April 2011

Improvements in the sensitivity and automation of high-resolution, ground-based spectrometers and interferometers allow the routine acquisition of measurements not only in the nightglow, but in the twilight. Measurements of the emission rate of the O2(1Δg) and O2(1Σg) bands have been used, primarily in the dayglow, to infer mesospheric O3 profiles. This paper describes a model for the inversion of twilight O2(1Δg) and O2(1Σg) emission-rate measurements to obtain O3 height profiles, concentrating on the sensitivity of the results to temperature profile, solar flux, photodissociations rates, uncertainties in the reaction rates, and constants, and the importance of transfer chemistry as a contribution to the O2(1Δg) emission rate, using a fixed O3 profile. The sensitivity of the calculations to inputs other than the desired O3 density shows this method may not be suitable for the absolute value of the O3 density (to better than about 25%), but can successfully determine the shape of the O3-density profile in the middle atmosphere.
Lidar measurements of the middle atmosphere
Authors: Carswell A. I. , Pal S. R. , Steinbrecht W. , Whiteway J. A. , Ulitsky A. , Wang T. Y.
Published: April 2011

This paper describes a new lidar facility that has been established for atmospheric measurements from the ground up to ~90 km altitude. Measurements of stratospheric aerosols and ozone are presented, and density and temperature profiles into the mesosphere are analyzed to derive information about atmospheric gravity waves.
SPEAM-I (sunphotometer Earth atmosphere measurement) observations of high-altitude ozone from STS 41-G
Authors: McElroy C. T. , Kerr J. B. , Wardle D. I. , McArthur L. J. B. , Shah G. M. , Garneau M. , MacLean S. G. , Thirsk R. , Davies J. A. , Evans W. F. J. , Nicholls R. W. , McConnell J. C. , Cann M.
Published: April 2011

The sunphotometer Earth atmosphere measurement (SPEAM-I) experiment was flown on the United States space shuttle Challenger in October, 1984 as part of a group of Canadian experiments referred to as CANEX-I. Measurements of the solar intensity were made through the orbiter side-hatch window at various wavelengths in the visible and near-ultraviolet during a number of terminator crossings using a hand-held, interference filter photometer. Observations at 315 and 324 nm were analyzed to give vertical profiles of ozone at 63.34°S, 91.96°E. These profiles are compared with data from the literature. The success of this experiment points the way to the use of small instruments to make accurate but inexpensive observations of the composition of the upper atmosphere.
Comparison between carbon monoxide measurements from spaceborne and airborne platforms
Authors: Connors V. S. , Cahoon D. R. , Reichle Jr. H. G. , Scheel H. E.
Published: April 2011

The measurement of air pollution from satellites (MAPS) experiment measured the distribution of middle tropospheric carbon monoxide (CO) from the space shuttle during October 1984. A critical area of the experiment is the assessment of experimental error of the MAPS data. This error is determined by the comparison between the space-based CO data and concurrent, direct CO measurements taken aboard aircraft. Because of the variability in the CO measurements near land sources, a strategy for comparing the tropospheric CO measurements over the remote oceans is presented.
Observations of seismo-electromagnetic earthquake precursor radiation signatures along Southern Californian fault zones: Evidence of long-distance precursor ultra-low frequency signals observed before a moderate Southern California earthquake episode
Authors: Dea Jack Y. , Richman Charles I. , Boerner Wolfgang-M.
Published: April 2011

Although questioned for a long time, there is accumulating growing evidence for the existence of detectable seismo-electromagnetic phenomena worldwide. California is geologically as well as seismically a unique region for studying these phenomena in depth; and, in particular, the southern California geologic province with a multitude of offshore and inland fault zones with San Diego in its center. At the Naval Ocean Systems Center Low Frequency Noise Laboratory, San Diego CA., we monitor 0.1–10 Hz ultra-low frequency (ULF) and 10–40 Hz extremely low-frequency (ELF) signals using mu-metal loaded multitum search coil sensors, as well as 10–100 kHz very low-frequency signals using large 1 m diameter loop antennas. We have observed precursor seismo-electromagnetic emissions of several earthquake events. In this paper, we report on observations of broadband ULF signals before and during the Upland quake of April 17, 1990 (Ms = 4.6), centered 200 km N of San Diego. The signals were detected with the vertically oriented search coil sensor and not with the horizontally oriented sensors, which suggests a disturbed ionosphere as the most likely source of these signals. The large prequake ULF activity, the rapid decay of ULF activity after the quake, and the absence of any geomagnetic storms indicate a good correlation of the ULF activity with the Upland quake. Although the exact mechanisms for coupling geologic activity to the ionosphere is not known, we cite a number of hypotheses concerning these mechanisms. Based on this succinct overview, an interpretation of our radio observations of seismic activity is presented and extended to earthquake precursor or predictor studies. We are in the process of expanding this research with the building of more monitoring stations and the improvement of our measurement, data collection, formatting, and data processing capabilities.
Viking UV cameras: Calibration using model calculations and long-wavelength light leakage
Authors: Griffioen E. , McConnell J. C. , Murphree J. S. , Shepherd G. G. , Cogger L L.
Published: April 2011

In this paper we present the results of a comparison of Viking UV images of the dayglow with model calculations of the dayglow in order to assess the uncertainties in the calibration of the cameras. The procedure that was adopted was to calculate the dayglow emissions using proven photoelectron and radiative transfer codes, and convolve these results with the prelaunch camera transfer functions to estimate the emission strength for the two cameras (1304 Å (1 Å = 10−10 m) and Lyman–Birge–Hopfield (LBH)). We found quite good agreement between the model and measured intensities for the 1304 Å camera. However, the results for the LBH camera suggest that there is substantial leakage of far UV (FUV) light at 2000 Å and "white" light around 3400 Å: only about 20–30% of the emission comes from the LBH dayglow. To evaluate the contamination from the longer wavelengths, we assumed that it was due to Rayleigh scattering off air molecules and reflection off surfaces. A multilayer multiple-scattering radiative transfer code allowing for Rayleigh scattering and absorption by O2 and O3 was used. The model intensities were then convolved with "known" and extrapolated camera filter response characteristics in the region from 1800 to 7500 Å to obtain model camera signal values due to long-wavelength light leakage. A preliminary estimate of the scattering contribution to the observed intensities using the first-order guess of the camera response function (CRF) beyond 2000 Å resulted in a substantial overestimation of the LBH camera intensities. To obtain a better estimate of the CRF we used an LBH image where clouds were known to be present. This allowed us to distinguish between the 2000 and 3400 Å contributions in order to obtain a modified CRF that reproduces the data for the LBH camera. The fact that both the 1304 Å dayglow camera intensities and the model results are comparable and the LBH intensities may be modelled allowing for Rayleigh scattering suggest that the calibration of the cameras in the FUV are defined to better than about 30% and so should reproduce nighttime auroral intensities at 1304 Å and for the LBH system with comparable accuracy.