J. B. Restorff

Measurement of effective mass in In0.9Ga0.1As0.22P0.78 by Shubnikov–de Haas oscillations

The 0 K electron effective mass in an In0.9Ga0.1As0.22P0.78 epitaxial layer has been calculated from the temperature dependence of Shubnikov–de Haas oscillation amplitudes, giving m*=0.060m0. The measured value is compared to values m*=0.059m0 and m*=0.058m0 obtained from interpolations of the masses of related binary compounds by two different methods.

Weak‐field magnetoresistance in noncubic (111)‐oriented epitaxial films of n‐type PbTe

Measurements of the weak‐field magnetoresistance (WFMR) were carried out at 300 and 77 K on two (111)‐oriented n‐type PbTe epitaxial films, 4 and 10 μm thick. A recently developed single‐sample four‐measurement technique and a cubic‐trigonal‐hexagonal extension of the Seitz–Pearson–Suhl WFMR phenomenology were used to obtain and analyze the data. Significant deviations from the requirements of cubic symmetry were detected, the effect being larger in the thinner film and at the lower temperature. A WFMR coefficient ratio, which would have been unity for a cubic environment, ranged from 1.3 to 6.8. These noncubic results are tentatively ascribed to the effects of substrate‐induced strain on the films. The four WFMR coefficients were fitted to a simple trigonally distorted three‐parameter model of the PbTe conduction band. For reasons not yet identified, the fit was very good for the thinner film and quite poor for the other one.

Unified weak‐field magnetoresistance phenomenology for cubic and noncubic (001)‐ and (111)‐oriented epitaxial films and surface layers

Extensions of the Seitz‐Pearson‐Suhl weak‐field magnetoresistance (WFMR) formula are applied to cubic and noncubic (001) ‐ and (111) ‐oriented epitaxial films and surface layers, including the extreme case of two‐dimensional conductivity in a quantized layer. It is shown that four distinct WFMR measurements may be made on samples in either plane, thus providing a simple and reliable means of distinguishing cubic from noncubic transport environments.

Thermal cycling‐induced changes in the electrical transport properties of (111) epitaxial, n‐type PbTe films

Weak‐field magnetoresistance measurements at 297 K were used in conjunction with an appropriate band structure model to detect the substrate‐induced strain in n‐type PbTe epitaxial films grown on BaF2. Evidence of strain in as‐grown films was found. The temperature of the sample was repeatedly cycled from 297 to 4.2 K and back, and the 297‐K strain was found to decrease. At the same time, Hall effect and resistivity measurements show that the 4.2‐K mobility dropped and the 297‐ and 4.2‐K carrier concentrations increased. The observed effects are ascribed to an extended defect density which grows larger as the number of thermal cycles increases.

Improved weak‐field magnetoresistance analysis for (001) ‐oriented thin films and surface layers with cubic or tetragonal symmetry

Weak‐field magnetoresistance (WFMR) behavior is described for (001) ‐oriented films and surface layers in which the sample current lies along a nonspecial direction in the plane. It is shown that four independent WFMR measurements may be made on one sample in this configuration. For cubic crystals, this permits the Seitz‐Pearson‐Suhl WFMR coefficients b, c, and d to be determined and to be checked for internal consistency. If for any reason, the symmetry of the environment becomes tetragonal (that is, the symmetry axis normal to the film plane becomes distinguishable from the in‐plane symmetry axes), then the four coefficients b, b′, c, and d appropriate for this case may be obtained. In either event, the data are more convenient to measure and are more reliable since they are extracted from a single sample. This new approach seems potentially useful as a sensitive indicator of electronic anisotropy over a broad range of environments, including cubically symmetric transport at one extreme and quantized tw...

Weak‐ and strong‐field magnetoresistance in (111)‐oriented n‐type PbTe epitaxial films between 1.8 and 300 K

Magnetoresistance measurements on epitaxial PbTe, covering a wide range of temperatures and magnetic field intensities, are reported. Nearly all of the results exhibit a common behavior which depends only on μHB, the product of the Hall mobility and magnetic field. The usual quadratic weak‐field dependence is followed by a tendency towards saturation near μHB = 1, and by a linear range for μHB = 10–300. The relevance of sample inhomogeneities, boundary effects, and quantum‐limit magnetoresistance theories is considered. None of these factors seems capable of explaining the general insensitivity of the results to temperature, scattering mechanisms, and sample profile.

The electron effective mass in In1−xGaxAsyP1−y

The electron effective masses in four epitaxial samples of In1−xGaxAsyP1−y lattice matched to InP (x?0.45y) have been measured by fitting temperature dependent Shubnikov‐de Haas data to the appropriate theory. For y=0.764, 0.705, 0.756, and 0.467 we have obtained band‐edge effective masses of 0.0464, 0.0471, 0.0478, and 0.0639me, respectively. The compositions were obtained from the band gap using an empirical relation due to Nahory et al. The method has been verified by applying it to bulk and epitaxial GaAs.

Suppression of large Barkhausen jumps in annealed amorphous wires with an imposed twist as a function of current, external axial stress, and axial field

The magnetization and small signal alternating‐current permeabilities of transverse‐field‐annealed amorphous magnetostrictive wires (Fe77.5B15Si7.5) with a fixed twist of 400 deg/m were examined as a function of applied axial tensile stress and axial direct‐current (dc) currents. We observe multiple‐featured magnetization curves which we attribute to the inverse Wiedemann effect, as well as a near total suppression of the large Barkhausen jumps when a dc current is flowing through the wire. Several properties of the wire depend on stress and would be useful for sensor applications; figures of merit of 1700–2600 for torque sensors were obtained.

Weak‐field magnetoresistance symmetry in epitaxial films and bulk crystals of p‐type SnTe

Nishiyama’s weak‐field magnetoresistance measurements on p‐type SnTe films deviate substantially from the requirements of cubic symmetry. A simple extension of the cubic theory to the case of substrate‐induced tetragonal distortion can account for the measurements. To establish internal consistency of the data with tetragonal symmetry requires an additional measurement which was not, but can easily be, made.

Hot electron and magneto-transport properties of In1−xGaxP1−yAsy liquid phase epitaxial films

Abstract We have measured the dependence of the electron velocity on electric field in four samples of In1−xGaxP1−yAsy at 77 and 300 K. In the same samples we have measured the temperature dependence of the Hall effect and the resistivity from 4.2 to 300 K. We have also studied the magnetic-field dependence of the magnetoresistance of several of the samples. The samples were n-type with carrier concentrations from 4.9 to 0.7 × 1016 cm−3. The compensation ratios were between 3.4 and 2.4. The lowest carrier concentration sample also had the lowest compensation ratio and exhibited a “peak” drift velocity of 3.6 × 107 cm/sec at an electric field of 4.0 kV/cm, higher than GaAs under similar conditions.