Showing papers on "Effective mass (solid-state physics) published in 1971"

Electrical Properties of High‐Quality Stannic Oxide Crystals

Abstract: Single crystals of the wide bandgap semiconductor stannic oxide, SnO2, have been grown and studied electrically. A chemical vapor deposition technique using chlorine transport, no inert carrier gases, and low pressure has been used to grow stannic oxide crystals of higher purity and with almost an order‐of‐magnitude higher low‐temperature Hall mobility, 8800 cm2/V sec at 80°K, than have previously been available. Measurements of Hall mobility, carrier concentration, and resistivity have been made between 20 and 625°K on crystals with room‐temperature carrier concentrations between 8×1015 and 2×1018 cm−3. The effects of the crystal anisotropy on these measurements have been investigated and found to be small (all results reported are for the a direction). A donor level ∼35‐meV deep due to antimony and another level ascribed to oxygen vacancies at ∼140 meV have been observed. Polar optical mode scattering with a dominant characteristic temperature of 1080°C is the main carrier scattering mechanism above 250°K. Below 250°K acoustic deformation potential scattering dominates. Ionized impurity scattering is eventually important in all samples as the temperature is lowered. A polaron effective mass of 0.39 me has been found consistently in the analyses of the data. A technique of fabricating good Schottky barriers on SnO2 has also been developed and used to measure the net donor concentration in samples. The agreement found between these measurements and Nd from Hall measurements indicates that shallow trapping is not a problem in these crystals.

Exciton-Phonon Interaction and Optical Spectra –Self-trapping, Zero-Phonon Line and Phonon Sidebands–

Abstract: Optical properties of interacting exciton-phonon system have been theoretically studied in terms of a simple model consisting of Frenkel excitons and Einstein oscillators. The problem is characterized by two non-dimensional parameters B and S representing the exciton band width and the interaction energy, respectively. Approximate solutions have been obtained through the diagonalization of the Hamiltonian in special sub-spaces, and they reasonably describe the behavior of the system for all values of B and S . Absorption and emission spectra and the effective mass of the composite particle vary from free exciton type to self-trapped exciton type as we go from B > S to B < S . The energy-momentum relation has been qualitatively studied below the one-phonon continuum, and the following new features have been found in the strong coupling region; (1) complete split-off of the lowest branch in the whole Brillouin zone, and (2) the split-off of the second discrete branch. Furthermore, a clue to the mechanism of...

The magnetophonon effect in epitaxial films of n-type inp

Abstract: Up to eleven magnetophonon peaks are observed in the transverse magnetoresistance of high purity epitaxial films of n-type inp at temperatures between 77 and 300 k The low frequency cyclotron effective mass of the electrons is found to be 00820 +or- 00010 m0 at 77 k and 00781 +or- 00010 m0 at 300 k

Plasma Edge Reflectance Measurements in GaxIn(1−x)As and InAsxSb(1−x) Alloys

Abstract: Room temperature measurements of plasma reflectance have been made on polycrystalline homogeneous n type samples of GaxIn(1−x) As and InAsxSb(1−x) alloys. An analysis for the case of general degeneracy in a Kane-type conduction band has been developed, to allow the determination of electron effective mass (m0*/m) at the bottom of the conduction band. Hence values of m0*/m vs. x have been determined for both alloy systems. From the experimental data, values of relaxation time and optical mobility have also been calculated.

Intermediate Coupling Theory: Padé Approximants for Polarons

Abstract: A general method is presented for obtaining an accurate intermediate-coupling theory from weak- and strong-coupling perturbation theory. The method uses two-point Pad\'e approximants to extrapolate (low-order) expansions about the weak- and the strong-coupling limits into the intermediate-coupling regime. The method is used to evaluate the ground-state energy and effective mass of the polaron with gratifying success. In addition, the weak-coupling perturbation theory of the polaron dispersion relation, ground-state energy, and effective mass are extended to fourth, sixth, and fourth order, respectively. A scheme based on two-point Pad\'e approximants is used to obtain an optimal polaron dispersion relation.

Cyclotron Resonance and the Cohen Nonellipsoidal Nonparabolic Model for Bismuth. II. Limiting - Point Masses

Abstract: An equation for the limiting-point (LP) cyclotron effective mass as a function of magnetic field direction is derived for the Cohen nonellipsoidal nonparabolic (NENP) model of the electron Fermi surface of Bi. The general NENP equation is used, in which the $L$-point valence and conduction bands are not assumed identical. For some orientations of the magnetic field, the NENP model, unlike the ellipsoidal nonparabolic (ENP) model, predicts a LP mass larger than the central-orbit extremal mass by as much as a factor of 2 for pure Bi. The previously published LP-mass data of Edel'man and Khaikin are found to be in good agreement qualitatively with the NENP model; the NENP fit is clearly superior to the ENP fit. Attempts to determine unambiguous values for the adjustable band parameters in the NENP model by fitting the experimental data were unsuccessful, but in general the experimental data indicate that the $L$-point valence and conduction bands have essentially identical parameters. For identical bands, the value $\frac{{E}_{F}}{{E}_{g}}=0.50$ is required in order to fit the data.

Rotational invariance in the centrifugal stretching of deformed nuclei.

Abstract: An explicit model is developed for the rotational and quasi-rotational states of heavy deformed nuclei. It is assumed that the effective mass contributing to the rotational inertia lies outside a central, geometric core which is rotationally invariant. The effective mass is modified as a result of nuclear stretching which is assumed to take place against harmonic restoring forces. Good agreement with experiment is obtained for the so-called hard rotators and even for the neutron deficit and transition nuclei. Explicit expansions are obtained for the energy spectra and the effective moments of inertia in the form of asymptotic series in the angular momentum variable. These series give better convergence for low angular momenta and hard rotators.

Band structure of the 3d-t2g sub-shell of V2O3 and Ti2O3 in the tight-binding approximation

Abstract: Previous two-dimensional calculations of the band structure of V2O3 were extended to three dimensions. The band scheme was made to include the a 1 band consisting of c-axis oriented functions, and the band width was estimated to be of order 2–4 ev. It was found that the a 1 band is nearly one-dimensional and its bonding part is almost completely full for Ti2O3; while the e π band has a large effective mass in the c-axis direction in spite of a large transfer integral between c-axis neighbours. It is almost empty for Ti2O3, and partly filled for V2O3. This calculation neglects covalency with the oxygens and therefore cannot be regarded as quantitative, but rather as an order-of-magnitude evaluation, and as an illustration of certain features of the Ek versus k dispersion within the bands that result from symmetry considerations. In the sesquioxides, in contrast for example with ReO3, interaction between metal ions is direct, and not only through the oxygen ions, and this is why we think the approx...

Stimulated Emission and Excited States of the I6 Donor Electron in ZnO

Abstract: Laser‐excited luminescence has been measured in ZnO at 1.2°K. Emission due to the annihilation of the I6 bound excition with simultaneous excitation or ionization of the donor electron has been observed in stimulated emission, which was excited by intense N2 laser light. From the hydrogenlike series of these emission lines, the binding energy and the effective mass of the donor electron are estimated to be 40 meV and 0.22m, respectively.

Broadening of Landau Levels in Two-Dimensional Electron Gas: Its Effect on Surface Capacitance

Abstract: Based on effective mass theory, broadening of Landau levels in two dimensional electron gas is obtained bar taking account of multiple scattering due to impurities. Using the diagram technique, one particle Green's function is derived and it is shown that the physical origin of the level broadening is characteristic of two dimensional electron gas. Using the Green's function, the notches occuring in capacitance-voltage characteristics at low temperatures are qualitatively discussed in terms of the broadening of Landau levels. The implication of this broadening of Landau levels is discussed in relation to transport phenomena of two dimensional electron gas in strong magnetic fields.

The Energy Distribution of Electronic States in a Liquid Metal

Abstract: A method is developed for calculating for a liquid metal the total number of electronic states below an energy E. The method remains valid when the electron-ion pseudopotential is energy dependent. It is based upon an idea of Lloyd (1967), which we have extended and developed into a form suitable for numerical calculation. Calculations for liquid bismuth reveal no sharp structure in the density of states. The bandwidth for five valence electrons per atom is 1.18 Ry, which corresponds to a bandwidth effective mass of 0.63 electron mass, compared with the first order perturbation estimate of 0.87.

Properties of the conduction electrons in the metals of group VIII

Abstract: The behaviour of the conduction electrons in the eighth group elements was deduced from the results of experiments on vacuum-deposited films, by combining measurements of the electrical resistivity with thickness determinations and optical investigations. The mean free path of the electrons, their concentration, their effective mass, and the proportion of them specularly reflected at the film surfaces (known as the scattering parameter) were calculated by solving a system consisting of the Sondheimer equation for the size-dependence of the film conductivity, the known formulae giving the mean free path at the Fermi level and the plasma wavelength of the electron gas, and the Dingle relation for the scattering parameter in the spectral region of the anomalous skin effect. The data thus obtained are in reasonable agreement with the generally accepted band structure of the transition metals.

Vapour-phase crystallization and some physical properties of titanium nitride

Abstract: One possible method by which titanium, nitride layers may be obtained is by vapour-phase deposition using chemical transport reactions. The TiN layers in the present work were obtained from the reaction of a titanium tetrachloride, hydrogen, nitrogen mixture above 700 °K. The microhardness and reflection coefficient of the layers obtained have been investigated, in addition to the ratio of carrier concentration to effective mass. The dielectric constant and the relaxation time have been determined from the theoretical analysis of the reflection curve.

On the deformation potential constant of the conduction band in InSb

Abstract: An analysis of experimental data for InSb is made and the deformation potential constant ϵ1 of the conduction band is determined. It is shown that the correctly calculated value of |ϵ1| is about 30 eV. In the calculations of the carrier mobility for heavily doped semiconductors it is essential to take into account the effect of the band nonparabolicity on the transition probabilities and the screening of the scattering potentials by conduction electrons, and additionally at high temperatures it is necessary to consider the influence of electronphonon interaction on the effective mass and energy gap. The small values of |ϵ1| reported by some authors, who studied transport phenomena at low temperatures, are obtained under the condition ħ/τ > kBT (τ is the time between successive collisions), i.e. when the theory used is invalid. [Russian Text Ignored].

Temperature Dependence of the Positron-Annihilation Angular Correlation in Metals

Abstract: The thermal smearing of the positron-annihilation\char22{}angular-correlation curves is studied. In the case where the medium is a homogeneous interacting electron gas in thermal equilibrium, the analysis applied by Stewart and co-workers to the thermal smearing is shown to correctly give the effective mass. In conjunction with previous calculations of the effective mass, our results indicate that the observed thermal smearing cannot be explained as mainly caused by electron-gas effects. It is shown how the model can be modified to take into account the positron-phonon interaction. This reduces the discrepancy between theory and experiment, but not sufficiently to account fully for the experimental data. It is argued that new experiments are needed before one can decide whether it is necessary to consider new mechanisms in order to explain the effect. A convenient formalism is presented, which allows one to calculate all positron quantities at moderate nonzero temperatures within a given approximation scheme. The "ladder" approximation is used to illustrate the argument and to estimate correction terms.

Ground states of shallow donors in silicon and germanium

Abstract: The ground state energies of phosphorus, arsenic and antimony in silicon and germanium crystals are calculated. The 'central cell corrections' due to the repulsive core potentials and spatial variations of the effective mass and dielectric function are taken into account and a good agreement with experiment is achieved. The ground state of bismuth impurity is also discussed.

Current Transport, Effective Dielectric Constant, and Temperature of Ta2 O5 Thin Films

Abstract: The I‐V characteristics of Ta–Ta2O5–Au thin‐film devices indicate high temperatures and large dielectric constants for both Schottky and Poole‐Frenkel dominated conduction. The effects of space charge and electron effective mass are also indicated.

Magnetoacoustic Amplification in Extrinsic Nondegenerate Semiconductors

Abstract: The expression of an effective conductivity tensor for the magnetoacoustic amplification in extrinsic, nondegenerate semiconductors has been derived by the Boltzmann equation taking proper account of the Hall effect. This expression can be applied to any values of the frequency of acoustic waves and of the magnetic field in the classical regime. Detailed discussion of the Doppler‐shifted ultrasonic cyclotron resonance (DSUCR) is given by taking n‐InSb as an example. It is shown that the effective mass and the relaxation time of electrons can be determined by DSUCR. A brief discussion is also given on the magneto‐acoustoelectric instability in n‐InSb.

Intervalley scattering in n type Ge from a Hall effect experiment to high pressures

Abstract: Hall effect measurements on n type Ge to 65 kbar are described. The Hall mobility of electrons through the transfer from (111) to (100) states has been measured and an assessment of the scattering parameters for the different intervalley and intravalley processes has been made following the analysis of Nathan et al. (1961). The Hall mobility of electrons in the (100) valleys is determined as 1020+or-170 cm2V-1s-1, the (100) effective mass is estimated to be approximately 50% greater than for n type Si and the (100)-(111) energy sub-band gap is 0.186+or-0.010 eV. Nonequivalent intervalley scattering between the (111) and (100) valleys is shown to reduce the mobility by a factor of two near band cross-over. Results are directly relevant in determining coupling constants between valleys in high electric field calculations, involving (100) and (111) minima, as in InP.

Screening Effect in a Disordered Electron System. II. Application to the Impurity Band

Abstract: The screening effect is included into the Klauder-Yonezawa model of impurity band conduction at zero temperature. It is shown that the binding energy of impurity potential goes to zero smoothly with the increase of the concentration of impurities, which differs from the result of Li, Love and Miller and coincides with the suggestion of Krieger. The screening effect on the vallue of the mobility is in good agreement with experiments on InSb at comparatively low concentrations. It is also shown that the model is not good at high concentrations, which is demonstrated by the calculation of the dielectric function and by the comparison of the mobility with experiments on InSb. Effective mass of the impurity band is defined by the frequency dependent conductivity.