Intervalley Coupling Constants Research Articles

An ensemble Monte Carlo study of high-field transport in β-SiC

The high-field transport of electrons in β-SiC is investigated by use of an ensemble Monte Carlo technique. We consider scattering by acoustic deformation potential, polar optical phonon, two different equivalent intervalley phonons (one first-order and one zero-order interaction), impurity scattering and impact ionization. The intervalley coupling constants and deformation potential constant are estimated by fitting the ohmic mobility to the measured experimental values over the temperature range 50–1000 K. Polar runaway occurs above 5 × 10 5 V/cm. The distribution can be partially stabilized by impact ionization processes, but the runaway is still observed. For a nonparabolic band model, the drift velocity has a gentle peak around 4 × 10 5 V/cm. The peak value is 1.9 × 10 7 cm/s, which is comparable to the experimental value observed in 6H-SiC (2.1 × 10 7 cm/s).

Monte Carlo study of nonequilibrium phonon effects in GaAs

A many-particle Monte Carlo technique for nonequilibrium phonon problems is proposed. The laser induced nonequilibrium LO phonon population in GaAs is calculated. The intervalley coupling constants of GaAs are estimated from the comparison of Monte Carlo calculation and available experimental results.

High Energy Distribution Function in an Electric Field and Electron Impact Ionization in AIIIBV Semiconductors

AbstractA calculation method of the exponential dependence of the high‐energy distribution function in an electric field E is proposed for polar semiconductors. It is shown that in many‐valley semiconductors with complicated conduction band structure a strong anisotropy of the electron impact ionization coefficient α(E) will be obtained. In the case of E ∥ (100) or E ∥ (110) a ballistic transport in the Γ‐valley can occur and the dependence of In α vs.(E01/E) holds. If E ∥ (111) the ballistic transport in the Γ‐valley is impossible and the high‐energy distribution function is always formed due to electron scattering from X‐valleys. Then the dependence of In α vs.(E02/E)2 will be realized for a wide range of fields. The characteristic fields E01 and E02 are connected with the intervalley coupling constants for Γ—X and X—X scattering, respectively. Impact ionization processes are considered in detail for InSb, GaAs, and InP. The results are compared with accessible experimental data.

Scattering parameters from an analysis of the hall electron mobility in Ga 1− xAl xAs alloys

Hall mobilities in high purity epitaxial layers of n-type Ga 1− x A x As alloys with room-temperature electron concentrations in the range (5–10) × 10 15 cm −3 have been measured at 300 K for alloy compositions in the range 0⩽ x ⩽ 0.78. Models for the variation of various material parameters with composition are developed. The acoustic deformation potentials for the Π and X conduction band minima, the intervalley coupling constants for electron scattering among the X-X and L-X minima and the longitudinal optical phonon temperature for these scatterings and the polar optical scattering in the X minima have been determined from a theoretical fit to the experimental data. The electron mobilities in the Π, L and X minima are found to decrease with the composition in the range 0≦ x ≲ 0.45, show a minimum at x ⩽ 0.50 and then increase again with composition. These mobility variations are reflected in the minimum in the Hall mobility at x ≅ 0.5 due to intense non-equivalent electron scattering involving the L and x minima. The minimum in the electron mobilities in the Π and X minima have been identified to occur mainly due to the space charge and intervalley scattering among the L and X minima, respectively. The number of equivalent x minima in Ga 1− x Al x As alloys are estimated to be three and are, thus, situated at the zone edge.

Dynamical response of electrons in GaAs in a high electric field

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Temperature dependence of the electron mobility in the Δ1cminima of germanium

At high pressures the band structure of germanium becomes similar to that of silicon at atmospheric pressure, making the Delta 1c minima accessible to direct electrical investigation. Measurements of the electron mobility are reported; it was found to vary from 800 cm2 V-1 s-1 at 300K to 6400 cm2 V-1 s-1 at 120K, corresponding to a temperature dependence of T-2.7. Analysis, assuming effective mass ratios mt*=0.288, m1*=1.353 and an acoustic deformation potential of 3.61 eV, gave intervalley coupling constants of 3.7*108 and 2.9*108 eV cm-1 for the 430K LO and the 320K LA phonons respectively. A negligible coupling constant was found for the low-energy LA phonon, as was also determined for silicon and GaP.

Uniaxial stress investigations of the three-level conduction band structure of GaAs

Measurements are reported of low-field resistivity and Gunn effect threshold field as a function of (100) and (111) uniaxial stress for a number of epitaxial and bulk GaAs samples. The results provide the first direct evidence that the L1c minima are situated lower in energy than the X1c minima and are therefore involved in the operation of GaAs transferred-electron devices. Intervalley separations are obtained at 300K, but these are dependent on density-of-states values. Further information on band structure parameters such as intervalley coupling constants should now be obtainable by fitting the high-field data to Monte-Carlo calculations currently in progress. Deformation potentials for the satellite minima have been determined.

The effect of pressure on the high electric field instabilities in n-type GaAs

The high electric field properties of n-type epitaxial GaAs diodes have been studied to 40 kbar. In contrast to previous results, the authors find that the threshold field increases to 15 kbar. This is explained by the dominant effect of the increases of effective mass in the high mobility Gamma 1c minimum with pressure. The constraints these results place on the intervalley coupling constants to be used in theoretical calculations are indicated. Results from a series of diodes suggest that the variation of ET with pressure depends sensitively on contact effects. The data are discussed qualitatively in terms of possible pressure effects on metal-semiconductor barriers.

High-field transport in gallium arsenide and indium phosphide

The dependence of drift velocity on electric field strength in gallium arsenide and indium phosphide is calculated using recent theoretical estimates of the intervalley coupling constants. Screened and unscreened electron-phonon interactions are considered. In gallium arsenide, the results are shown to be in acceptable agreement with experimental data, the agreement being somewhat better if the unscreened interaction is used. In indium phosphide, the theory predicts very strong intervalley scattering and although this leads to a smaller negative differential mobility than in gallium arsenide, a much higher peak to valley ratio is predicted.

Room temperature high-field Hall mobility in n-type silicon

The high-field Hall mobility of n-type silicon has been studied by assuming Maxwellian distribution function of the carriers in the valleys. Different values of inter-valley coupling constants have been used. It has been found that a good fit to the experimental results for the direction may be obtained by a proper choice of the inter-valley coupling constants. But even then there remain some discrepancies in the detailed characteristics.