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Notes: The magnetic ordering in the series of solid solutions Fe3−xMnxSi having the D03 structure has been extensively studied at low fields over a wide range of temperatures. The present study reports observations of high-field-induced transitions in the low temperature range below the reordering temperature TR for members of the series falling within the concentration range 1.6≤x≤1.8. These alloys appear antiferromagnetic in low fields below TR but application of a field within the range up to 12 T results in a transition to an apparently ferromagnetic state. The transition occurs at all temperatures below TR and occurs reversibly except at the lowest temperatures where the hysteresis may be ∼0.5 T. The variation of the critical field with temperature follows an approximately quadratic form. Above TR Arrott plots suggest for the alloy with x=1.70 that a narrow ferromagnetic regime exists over the range 65≤T≤85 K above which the material is paramagnetic. For the alloy with x=1.75 however the Arrott plots suggest a direct conversion to paramagnetism at the reordering temperature TR indicating a possible phase diagram similar to that of Au2Mn. A discussion is given in terms of a model previously proposed to explain the low-field behavior.

Notes: We have studied the mechanisms of interface trap (Nit) formation in metal-oxide-semiconductor devices during isochronal annealing after irradiation at 78 K. Two distinct Nit formation processes are observed at 120 and 250 K. After irradiation but before annealing, some samples were injected with electrons to remove all the radiation-induced positive oxide charges. In these samples, the Nit formation process at 250 K is nearly eliminated, in agreement with previous reports, but the lower-temperature 120 K process increases substantially. Results are explained using a hydrogen model. We also discuss the use of substrate hot-electron injection, which is used to annihilate the radiation-induced positive charge, in some detail.

Notes: Germanium-doped ZnSe epilayers have been grown on (001)-oriented semi-insulating GaAs substrates by molecular beam epitaxy. The photoluminescence (PL) spectra exhibit strong near-band edge emission similar to those from undoped, chlorine-doped and gallium-doped samples, though some differences exist. The prominent PL peak at 2.795 eV (10 K) is attributed to the germanium-bound exciton recombination and is accompanied by free exciton (2.802 eV), Ia-type exciton (2.785 eV) and Iv-type exciton (2.775 eV) emission peaks. Following an increase in temperature, the intensity of all the IGe, Ia, and Iv emission peaks decreases gradually, indicating the presence of nonradiative recombination mechanisms with thermal activation energies of 40, 70, and 50 meV respectively. However, for the Iv peak, there is one additional nonradiative recombination mechanism in accordance with the thermally activated transfer of excitons from the Iv-type centers to Ia-type centers. This nonradiative recombination mechanism with activation energy of 9 meV is responsible for the decrease of the Iv peak intensity when the sample temperature is changed from 15 to 100 K. Following an increase in temperature, the Iv peak, Ia peak, and germanium-related peak disappear gradually and successively. Finally, the PL spectrum is dominated by free exciton emission at temperatures exceeding 210 K. © 2002 American Institute of Physics.

Notes: The density of gap states distribution in silicon (Si) rich hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films with varying carbon (C) fraction (x) is investigated by the photothermal deflection spectroscopy (PDS). The films are grown using the Electron Cyclotron Resonance Chemical Vapor Deposition (ECR-CVD) technique. By using different methane-to-silane gas flow ratios, a-Si1−xCx:H with x ranging from 0 to 0.36 are obtained. A deconvolution procedure is performed based on a proposed DOS model for these Si rich a-Si1−xCx:H. Good fits between the simulated and experimental spectra are achieved, thus rendering support to the model proposed. Deduction of the DOS enables us to obtain various parameters, including the optical gap and the valence band tail width. The fitted mobility gap Eg is found to be well correlated to the Tauc gap Etauc and E04 gap deduced from the optical absorption spectra. A correlation is also seen between the fitted valence band tail width Evu, the Urbach energy Eu and the defect density. All these parameters are seen to increase with C alloying. A shift in the defect energy level in the midgap with increasing C incorporation is observed, together with a broadening of the defect distribution and a stronger correlation between the defect bands, which can be accounted for in terms of the influence of C dangling bonds on the deep defect density distribution. © 2002 American Institute of Physics.

Notes: Diamond-like carbon (DLC) films were deposited using the electron cyclotron resonance (ECR) chemical vapor deposition process. The behavior of the ECR plasma was formulated using deposition conditions such as microwave power, pressure, and hydrogen/methane (H2/CH4) ratio as input parameters. Thereafter, the outputs were used to formulate a DLC film deposition model, which takes into account the ion bombardment at the film surface, attachment of carbon-carrying ions, and chemisorption of hydrocarbon radicals on the film and hydrogen–surface reactions. The DLC film deposition model suggests that under conditions of high hydrogen atom flux, the main precursors are carbon-carrying ions. Hydrocarbon radicals, such as CH3, only contribute to ∼20% of the total film deposition rate. © 2002 American Institute of Physics.

Notes: Carbon nanoparticles were prepared from H2 and CH4 by microwave plasma chemical vapor deposition at various temperatures as low as 250 °C by using nickel and iron as catalysts. The carbon nanoparticles are well graphitized until a temperature as low as 400 °C, and the degree of graphitization increases with increasing growth temperature. Field emission measurements showed that the carbon nanoparticles are excellent electron field emitters, comparable to carbon nanotubes. Field emission properties became better with increasing growth temperature, and the threshold fields of the carbon nanoparticles deposited at 400, 500, 670 °C, were 3.2, 3, and 1 V/μm, respectively. No emission was observed for the carbon nanoparticles deposited below 400 °C. The low threshold field of the carbon nanoparticles is attributed to field enhancement effect and the higher degree of graphitization. © 2002 American Institute of Physics.

Notes: The electronic structures of the Ga1−xInxNyAs1−y/GaAs compressive strained quantum wells are investigated using 6×6 k⋅p Hamiltonian including the heavy hole, light hole, and spin-orbit splitting band. By varying the well width and mole fraction of N in the well material, the effects of quantum confinement and compressive strain are examined. The curves of dependence of transition energy on well width and N mole fraction are obtained. The valence subband energy dispersion curves and TE and TM squared optical transition matrix elements of three possible quantum well structures for emitting 1.3 μm wavelength are given. © 2001 American Institute of Physics.

Notes: Sm–Co particles have been produced in a W matrix by annealing sputtered Sm–Co/W multilayers with layer thicknesses of 5–28 nm at temperatures of 600–850 °C. The Sm–Co particles had the intermetallic 1:7 and 2:17 structures with sizes below 10 nm and coercivities in the range of 2–10 kOe. A reduction of magnetization with prolonged annealing has been observed and attributed to alloying of Co with both W and Si by interdiffusion through the W layer. © 2001 American Institute of Physics.

Notes: We report on the electrical and optical properties of silicon (Si)-doped InP layers grown by solid-source molecular beam epitaxy using a valved phosphorus cracker cell. Within the range of Si effusion cell temperatures investigated (900–1200 °C), the highest electron concentration obtained was 1.1×1020 cm−3. A saturation phenomenon was observed for the electron concentration at higher Si cell temperatures. 300 and 77 K Hall mobility data were used to determine the compensation ratios by comparing them with the theoretical data. Although the Hall data show that the compensation ratio increases with the increase in carrier concentration, the exact values are not certain because the theoretical calculation overestimates the mobility values at higher carrier concentrations. The saturation phenomenon of electron concentration in InP may be considered due to the Si atoms occupying both the In and P lattice sites, or Si donors located at the interstitial sites. The 300 K Hall mobility and the concentration data measured were found to fit the Hilsum expression well. The mobility values obtained in this study are better than or comparable to reported data in the past, indicating good material quality. 5 K photoluminescence (PL) measurements showed two peaks for the undoped and low doped InP layers corresponding to the neutral donor-bound exciton transitions (D0–X) and the acceptor-related transitions (D–A), respectively. When the doping level was increased, the near-band edge (D0–X) recombination peak becomes broadened and asymmetric due to changes in the donor level density of states and relaxation of the wave vector conservation rule. The full-width at half-maximum (FWHM) value of the PL peak position increased when the doping concentration was increased. An empirical equation was developed to fit this variation, which provides a convenient way of determining the dopant concentration from the experimental FWHM value. The near-band edge peak positions shifted to higher energy with the increase of doping level due to the band filling effect. This shift agreed well with the calculations based on the Burstein–Moss shift and the band gap narrowing effect considering a nonparabolic conduction band. © 2000 American Institute of Physics.

Notes: Hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films have been deposited using an electron cyclotron resonance chemical vapor deposition system. The effects of varying the microwave power from 100 to 1000 W on the deposition rate, optical band gap, film composition, and disorder were studied using various techniques such as Rutherford backscattering spectrometry, spectrophotometry, Fourier-transform infrared absorption, and Raman scattering. Samples deposited at 100 W are found to have a carbon fraction (x) of 0.49 which is close to that of stoichiometric SiC, whereas samples deposited at higher microwave powers are carbon rich with x which are nearly independent of the microwave power. The optical gaps of the films deposited at higher microwave powers were noted to be related to the strength of the C–Hn bond in the films. The photoluminescence (PL) peak emission energy and bandwidth of these films were investigated at different excitation energies (Eex) and correlated to their optical band gaps and Urbach tail widths. Using an Eex of 3.41 eV, the PL peak energy was found to range from 2.44 to 2.79 eV, with the lowest value corresponded to an intermediate microwave power of 600 W. At increasing optical gap, the PL peak energy was found to be blueshifted, accompanied by a narrowing of the bandwidth. Similar blueshift was also observed at increasing Eex, but in this case accompanied by a broadening of the bandwidth. These results can be explained using a PL model for amorphous semiconductors based on tail-to-tail states radiative recombination. A linear relation between the full width at half maximum of the PL spectra and the Urbach energy was also observed, suggesting the broadening of the band tail states as the main factor that contributes to the shape of the PL spectra observed. © 2001 American Institute of Physics.