B. Soudini

Pressure dependence of positron annihilation in InP

Abstract We have obtained the valence electron and positron charge densities in InP from wavefunctions derived in a model pseudopotential bandstructure calculation at normal and under hydrostatic pressure. We find that the positron density is maximum in the open interstices and is excluded not only, as usual, from the ion cores but also to a considerable degree from the valence bonds. Electron-positron momentum densities are calculated for the (001–110) plane. The results are used to analyze the positron effect in InP.

Positron annihilation studies in GaxIn1−xAs

Abstract The effect of alloying on the electron-positron momentum densities, ϱ(p), in GaxIn1−xAs is reported. Our computations of ϱ(p) are based on the independent particle approximation (IPM) coupled with the empirical pseudopotential method (EPM). To make allowance for the chemical disorder, the virtual crystal approximation is used, including a correction to the alloy potential. An illustrative result of the electron-positron momentum densities show a deviation from linearity at low momentum which indicates the alloying effect (bowing effect).

Positron annihilation studies in diamond

Abstract A computational technique is developed to evaluate positron distribution as well as the electron—positron momentum densities in diamond and the use of these provide us the means of interpreting the k -space densities obtained experimentally using the two-dimensional angular correlation of annihilation radiation (2D-ACAR). The method is based on the independent particle approximation (IPM) coupled with the empirical pseudopotential method (EPM) including a non-local correction. Results show a fairly good agreement with the experiments.

Pressure dependence of band gaps in GaAs, GaP, InP, and InAs

Abstract We have used an adjusted pseudopotential method to calculate linear and quadratic pressure coefficients of GaAs, GaP, InP and InAs. Our calculation is computationally simple and yields results that are in good agreement with experimental measurements.

Conduction band edges charge densities in CdxZn1−xS

Abstract The empirical pseudopotential method coupled with the virtual crystal approximation is used to compute the electronic conduction band-edge charge densities at the Γ and X points for the ternary alloy CdxZn1−xS. We find that these charge densities are strongly dependent upon the stochiometric coefficient x. Such differences are crucial for a comprehensive understanding of interstitial impurities and the response of specific band states to perturbation in ternary alloy semiconductors.

Electronic structure of the pseudobinary semiconductor alloy GaxAl1 − xSb

Abstract A method for calculating the detailed electronic properties of the pseudobinary semiconductor alloy Ga x Al 1− x Sb os presented. The technique begins with realistic band structures obtained for the constituent compounds by fitting the band gap symmetry point energies to experimental data within the pseudopotential scheme. Then the virtual crystal approximation, which incorporates compositional disorder as an effective potential, is used to calculate the alloy band structures and charge densities. A detailed comparison between the theoretical predictions and experimental data demonstrates the quantitative nature of the method. The bowing parameters for the Λ, X and L gaps and the direct-to-indirect band gap cross-over concentrations are in good agreement with the experimental results.

The alloying and pressure dependence of band gaps in GaAs and GaAsxP1−x

Abstract We have calculated the electronic band structures for GaAsxP1−x alloy system using the empirical nonlocal pseudopotential method. The nonlocality of the potential is described by the Gaussian model. We find that the energy gap varies sublinearly with x, with the direct-indirect transition occuring at x = 0.58. The dependence on hydrostatic pressure of the direct and indirect energy band gaps of GaAs have been calculated with the pseudopotential method. The optimized nonlocal pseudopotential reproduce the energy gap dependence with pressure within a small deviation compared to the experimental values.

Correlation between positron affinity and ionicity in semiconductors

Abstract The independent particle method (IPM) coupled with empirical pseudopotential method (EPM) was used to compute the thermalized positron charge densities in specific family of binary tetrahedrally coordinated crystals of formula ANB8−N. Initial results show a clear asymmetrical positron charge distribution relative to the bond center. This positron affinity lead us to establish an empirical formula for the calculation of the ionicity character in these semiconductors. A good agreement was found between our calculations and the Phillips ionicity scale.

Resonant tunneling effect through a parabolic quantum well

We present a theoretical investigation on the resonant tunneling effect in an AlAs double-barrier structure with a AlGaAs central well having a special parabolic geometry. The results are similar to those obtained in a transverse resonant magnetotunneling experiment (with a magnetic field parallel to the interfaces of a square well).

Correlation between high-pressure effects and alloying in GaP and AlP

Abstract The variation of the direct and indirect band gap of GaP and AlP has been calculated using the adjusted empirical pseudopotential method. The gap varies sublinearly with pressure but linearly with lattice constant. These results are discussed in the light of experimental results. The direct band gap increases with increasing pressure, whereas the indirect gap decreases. The effect of high pressure is correlated with the effect of alloying in GaxAl1 − xP.