Showing papers on "Effective mass (solid-state physics) published in 1979"

The electron effective mass in heavily doped GaAs

Abstract: A resolution to the order k6 of the three-level equation of Kane allows the authors to obtain a new expression for the conduction band energy and so new analytical expressions for the electron effective masses in the range of carrier concentration 1016-1019 cm-3. The calculated values of the conduction effective mass as a function of carrier density agree well, for the first time, with experimental values, which were obtained from Shubnikov-de Haas experiments by using a new expression for the oscillation amplitude. In this expression the authors take into account the effect of medium-range potential fluctuations induced by crystal inhomogeneities.

An experimental determination of the effective masses for GaxIn1−xAsyP1−y alloys grown on InP

Abstract: The band‐edge effective mass for conduction electrons in GaxIn1−xAsyP1−y has been determined for several different alloy compositions covering the complete range of alloys grown lattice‐matched on InP. Measurements show that the effective mass varies nearly linearly with alloy composition.

Picosecond Time of Flight Measurements of Excitonic Polariton in CuCl

Abstract: The group velocity of excitonic polariton in CuCl has been measured at 4.2 K using picosecond light pulses. It is derived by measuring both the time delay of light pulses and the thickness of samples. Experimental results are well explained by the dispersion relation of excitonic polariton including spatial dispersion. In addition, the translational effective mass of exciton in CuCl is directly derived, i.e. M =(2.0 ±0.1) m 0 .

Generalized electron gas-Drude model theory of intermolecular forces

Abstract: An electron gas theory of intermolecular forces which unifies the treatment of long‐ and short‐range effects is improved and extended in several ways. (1) The shell polarization model takes full account of the forces from both cores and shells. (2) The amount of polarization is calculated with full self‐consistency in the forces on the shells. (3) Exact agreement with the known long‐range forces is achieved by an effective mass description of the shell dynamics. (4) Anisotropic polarizations appropriate to a linear molecule interacting with an atom are included. The theory is applied to the systems H2–He, H2–Ar and HCl–Ar. Fairly good agreement is found with the available but incomplete experimental data including the angle dependence of the potentials. However, some evidence suggest that the predicted repulsion is somewhat too large when a rare gas atom approaches a hydrogen atom along the molecular axis.

Cyclotron resonance in n‐type In1−xGaxAsyP1−y

Abstract: First experimental data are presented on the nonparabolicity of the conduction band of In1−xGaxAsyP1−y lattice matched to InP. The values for the effective mass, determined from our energy‐dependent measurements, are smaller than all previously reported values. The nonparabolicity of the conduction band is much stronger than previously assumed.

Electronic profile of n‐InAs on semi‐insulating GaAs

Abstract: The electron density and mobility of VPE‐grown 15‐μm n‐type indium arsenide epilayers have been determined as a function of distance from the gallium arsenide substrate. Both epilayer surfaces show significant increases in density and decreases in mobility from the bulk values (1015–1016 cm−3 and 105 cm2/V sec at 77 °K). The interfacial, or back, surface is apparently dominated by defects to a depth of about 3 μm. The density and mobility profiles are roughly exponential; integrated values are 1.6×1013 cm−2 and 2×103 cm2/V sec. The front surface, highly dependent on applied gate bias, has a density range in accumulation from zero to 5×1012 cm−2 and mobility from 2.5×104 to 3×103 cm2/V sec. The parameters for both surfaces are essentially temperature independent below 80 °K. The front‐surface effective mass increases with electron density from its band‐edge value of 0.0215me to nearly 0.06 me.

Calculated electron-phonon contributions to phonon linewidths and to the electronic mass enhancement in Pd

Abstract: This paper presents a calculation of the linewidths of phonons in Pd owing to decay into electron-hole pairs. Korringa-Kohn-Rostoker energies and wave functions are used with the rigid-muffin-tin approximation (for the electron-phonon matrix element). The linewidths of the longitudinal $[\ensuremath{\zeta}00]$ phonons show a sharp maximum which is in qualitative agreement with the recent experimental observations of Youngblood et al. Relatively large linewidths are calculated for a transverse mode (${T}_{1}$) along the [110] direction, which are in good agreement with the previous experiment of Miiller. Both the matrix element and the joint density of states at the Fermi energy contribute to the magnitude of the calculated linewidths. The electron-phonon contribution to the electronic mass enhancement is calculated to be 0.41. This result is used to estimate the contribution due to paramagnetic fluctuations.

Temperature dependence of the electrical conductivity and thermoelectric power in MoTe2 single crystals

Abstract: Thermoelectric power and de electrical conductivity measurements are made on MoTe2 single crystals in a wide temperature range (77 to 770 K). The results are analyzed on the basis of impurity conduction. It is shown that three processes contribute to the total conductivity: hopping conduction between impurity sites, scattering by optical modes, and, in the intrinsic domain, scattering by impurities. The thermal energy gap (0.99 eV) is approximately the same as the optical one (1.03 eV). The effective mass of electrons in the conduction band is not very different from the mass of the free electron (m* = 0.76m), and the dielectric constant of the medium is K ≈ 34. The agreement between theoretical and experimental results is quite good. A comparison with previous results performed on compact polycrystalline samples is given.

Positronium in α-Quartz. I. Observed Temperature Dependence of the Positronium Effective Mass and the Probability of Annihilation from Singlet Positronium State

Abstract: The momentum distribution of photon pairs from positrons annihilating in synthetic crystalline quartz has been measured over a wide temperature range. The width of the narrow component in the distribution was analyzed to yield the positronium effective mass. The effective mass is found to be (1.6 7 ±0.15)×2 m e at low temperature, but appears to increase as the temperature is raised. This result will be discussed in Part II from the view-point of positronium-phonon interaction. The probability of annihilation from singlet positronium state (i.e., the intensity of the narrow component) also increases as the temperature is raised, and tends to approach to a constant value at sufficiently high temperatures. This result might be attributable to possible temperature dependence of positronium formation probability in quartz.

Evidence for a reduction in the momentum matrix element P2 due to alloy disorder in InAp1-xPx

Abstract: Measurements of cyclotron resonance and the infrared absorption in the region of the direct band gap are reported for the complete range of alloys InAs1-xPx. The experimentally determined values of the effective mass are found to be almost linear functions of the alloy composition. This is in contrast to the predictions of k.p theory which, using a linear interpolation of the momentum matrix element (P2) between the values for the two alloy constituents, predicts a strong bowing. The discrepancy is thought to arise from a reduction in P2 brought about by a mixing of the conduction and valence bands by random local disorder.

Magnetophonon Resonance and Fourier Analysis in n-GaAs

Abstract: With the use of magnetic field modulation technique up to eighteen magneto-phonon peaks are observed in the transverse and longitudinal magnetoresistance of high purity epitaxial n-GaAs. Fourier analysis reveals the second harmonic component resulting in a sharpening of the oscillatory structure in the transverse magnetoresistance and extrema associated with the two LO phonon process in the longitudinal magnetoresistance in addition to the ordinary magnetophonon series. Two methods are described to obtain the damping factor \barγ which is found to be 0.63 from the Fourier analysis and 0.60 from the method described in this paper for the specimen with the highest mobility (1.7 ×10 5 cm 2 /V ·s) at 77 K. The temperature dependence of \barγ for the high purity n-GaAs exhibits a variation T 0.25 at low temperatures, which indicates an importance of the band failing effect for the damping process. The effective mass is determined to be m * =0.0682 m 0 at 77 K.

Positronium in α-Quartz. II. Possible Effect of Damping of Positronium Quasiparticle on the Momentum Distribution

Abstract: A part of the observed momentum spread of thermalized positronium in crystalline quartz reported in Part I could be attributed to a damping effect of the positronium quasiparticle in the phonon field. As analogized from the case of excitons, the damping constant (the width of the spectral function) for the quasi-particle state is expected to be proportional to the absolute temperature T in the moderate and high temperature regions due to the well-known motional effect in the phonon field. Therefore if we analyze, as in Part I, the observed momentum distribution by using a Maxwellian with effective mass M * ( T ), the resultant M * ( T ) would appear to increase with increasing temperature owing to the above-mentioned temperature dependence of the damping effect.

Perturbation Expansion for the Asymmetric Anderson Hamiltonian

Abstract: (Received March 5, 1979) The single orbital Anderson Hamiltonian with d-orbital fixed to the Fermi level (E"=O) is discussed by a perturbation method with respect to electron correlation U. In this model the Coulomb repulsion U reduces the occupied d-electron number and, on the other hand, enhances the d-electron effective mass and normalized susceptibility (X,). As the result of competition of these effects, the specific heat at low temperature decreases and the magnetic susceptibility increases with U for U

Scattering mechanisms of electrons in ZnSe crystals with high mobility

Abstract: In low-ohmic n-type ZnSe crystals with the room temperature specific resistance of (3 to 5) Ω cm and electron concentration from 3 × 1015 to 2 × 1016 cm−3 Hall-effect, electrical conductivity, and charge carrier mobility is investigated in the temperature interval from 10 to 300 K. The basic parameters of the samples are determined. It is found from the experimental data that the mobility is higher than the theoretical value in the investigated temperature range. It is argued that in the region of ionized impurity scattering this descrepancy between theory and experiment is due to the inadequacy of known scattering based on the Born approximation, as for ZnSe this approximation is valid at T > 140 K, where the phonon scattering is predominant. To square the theory with the experiment in the phonon scattering region a polaron effect is taken into account, which manifests itself in renormalization of the carrier effective mass as well as in alteration of the mobility temperature dependence due to the effect of screening of the interaction with polar vibrations. The theoretical consideration of this question is given which allows to bring the theory and the experiment to a satisfactory correspondence. [Russian Text Ignored]

The single-particle potential, symmetry coefficient and effective mass in nuclear matter

Abstract: The single-particle potential, its isotopic spin dependence, symmetry coefficient and effective mass in nuclear matter have been calculated using a simple effective interaction consisting of a density-dependent delta-function repulsion and a gaussian attraction. The density dependence in the interaction has been considered in three different forms: rho 2/3, rho 1/3 and rho 1/6. The three parameters of the interaction are determined so as to reproduce the correct binding energy and density in nuclear matter and the ground-state energy of 16O. With the above interaction, simple relations for the single-particle potential, symmetry coefficient, effective mass and other related quantities in nuclear matter are derived. It is found that the Hugenholtz-Van Hove theorem is satisfied exactly and the results for these quantities are in good agreement with those referred to in the literature.

A simple theoretical analysis of the low-energy spin fluctuation peak observed by neutrons in liquid 3He

Abstract: We present a simple analysis of the low-energy spin fluctuation peak recently observed at Argonne in neutron experiments performed on liquid 3He at low temperature. From the energy position of the peak, we extract values for the spin-spin interaction (supposed to be of contact type) and the effective mass which agree amazingly well with those used in the paramagnon picture, which assumes liquid 3He to be close to ferromagnetic. This allows a theoretical curve for the incoherent part of the neutron inelastic scattering function to be drawn without any adjustable parameter: the only one that has been extracted from the neutron data. Then, by subtraction from the experimental total scattering function, we obtain an approximate shape for the coherent part containing the zero-sound mode also observed in these experiments. More data, in particular for smaller momentum transfer would be most useful for confirming the above result, and also possibly for building up a one-parameter model for the zero-sound mode, analogous to the one-parameter model (paramagnon) for the spin fluctuation pseudo mode.

Transverse mass of a bubble in a rotating gradient

Abstract: We propose principles for interpreting magnetic‐bubble dynamics in a rotating‐gradient experiment when no external in‐plane field is present. If the orbit of the bubble is circular, simultaneous determinations of radius and phase lag with respect to the drive may be interpreted to measure the mobility coefficient and the velocity‐momentum [V=V (P)] relation. Investigation of the stability of the circular orbit shows that in one limiting case the segments of V (P) having a positive slope will be accessible to experiment. We illustrate dependences of V on P expected for static bubbles with 1) small numbers of vertical Bloch lines, 2) horizontal Bloch lines, and 3) large numbers of vertical Bloch lines. We conclude that rotating‐gradient measurements can determine the Bloch‐line structure of the circulating bubble. The basically new element present in such experiments is the transverse component of effective bubble mass, which differs from the longitudinal component and will be much greater than the Doring mass whenever Bloch lines are present.

Two-dimensional effects and effective masses of the InAs/GaSb (001) superlattices

Abstract: The tight binding method is employed to study the two‐dimensional aspects of the electronic structure of InAs/GaSb(100) superlattices. Results are presented which show the spatially confined nature of the light hole, heavy hole and conduction bands. The hole states are found to be confined primarily on the GaSb side, whereas the conduction bands are confined to the InAs side. Effective masses in the plane of the superlattice are calculated. The conduction band mass is found to compare well with the appropriate value extracted from recent magnetoresistance measurements. Optical absorption data is used to determine the InAs conduction band to GaSb valence band edge discontinuity at the Γ‐point. It is found that the former lies below the latter, qualitatively consistent with the electron affinity rule, but only by ∠ 60 meV. Reduction to this value from the affinity value of ∠ 140 meV is consistent with the affect of charge transfer. Finally, some comments regarding the variation, with thickness, of the relative and absolute positions of energies are made, particularly in light of the prevalent, though often ambiguous, practice of comparing projected regions of bulk energies with finite slab or superlattice band structures.