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The band structure of Al x Ga 1 − x Sb semiconducting ternary alloys and their related properties such as elastic constants, microhardness, transition pressure to the first phase, acoustic wave velocities and melting temperature have been investigated. The calculations are performed using a pseudopotential approach within the virtual crystal approximation which includes the effect of compositional disorder as an effective potential. Generally, our results are found to be in good accord with the experimental results. The composition dependence of all features of interest showed a monotonic behavior and suggests that the stiffness, hardness and structural stability becomes better in Al x Ga 1 − x Sb for higher Al concentrations. The bulk sound speeds and melting temperature are found to become larger when increasing the Al content. [ABSTRACT FROM AUTHOR]

A pseudopotential calculation of the electronic structure of AlGaSb ternary alloys in the zinc-blende structure has been performed. The compositional dependence of energy gaps, electron and heavy hole effective masses and ionicity of the material system of interest have been examined and discussed. Special attention has been given to the effect of the alloy disorder on the direct (-) bandgap energy. It is found that all features of interest vary monotonically with increasing the Al concentration . Besides, bandgap bowing parameters and extent of the direct-to-indirect bandgap transition have been determined. Our findings agree generally well with the data reported in the literature. Trends in ionicity are found to be consistent with the Phillips ionicity scale. [ABSTRACT FROM AUTHOR]

The present study deals with first-principles calculations of the thermal properties of ZnTe in the two phases namely, zinc-blende and wurtzite. The calculations are mainly performed using the density functional theory with the local density approximation and response-function calculations. The full phonon dispersions throughout the Brillouin zone are presented. The temperature dependence of the lattice parameters, bulk modulus, entropy and heat capacity are examined and discussed. Our findings agree reasonably well with those available in the literature. [ABSTRACT FROM AUTHOR]

Based on the pseudopotential scheme under the virtual crystal approximation that takes into account the effect of compositional disorder combined with the bond-orbital model of Harrison, the results of calculations of elastic constants and surface and bulk acoustic wave speeds of Cd1-xZnxTe mixed crystals in the zinc-blende structure are presented. The agreement between our results and known data, which are only available for CdTe and ZnTe is found to be reasonable. [ABSTRACT FROM AUTHOR]

We present an investigation of the electronic properties and optical constants of zinc-blende ZnSxSe1-x semiconducting alloys at normal and under hydrostatic pressure up to 20 kbar. For this purpose, we used an empirical pseudopotential method within the virtual crystal approximation. The effects of alloy composition are taken into consideration in the calculation, which improves significantly the bandgap bowing parameters with respect to the experiment. Results regarding the composition and pressure dependences of energy bandgaps, electron valence and conduction charge distributions, optical high-frequency dielectric constant and its linear pressure coefficient are presented and discussed. The information derived from the present study may be useful for the development of opto-electronic devices that operate in the blue/green spectral range. [ABSTRACT FROM AUTHOR]

We present an investigation of the electronic properties and optical constants of zinc-blende ZnSxSe1-x semiconducting alloys at normal and under hydrostatic pressure up to 20 kbar. For this purpose, we used an empirical pseudopotential method within the virtual crystal approximation. The effects of alloy composition are taken into consideration in the calculation, which improves significantly the bandgap bowing parameters with respect to the experiment. Results regarding the composition and pressure dependences of energy bandgaps, electron valence and conduction charge distributions, optical high-frequency dielectric constant and its linear pressure coefficient are presented and discussed. The information derived from the present study may be useful for the development of opto-electronic devices that operate in the blue/green spectral range. [ABSTRACT FROM AUTHOR]

Electron penetration in semi-infinite Au for normal and oblique angles of incidence at energies between 0.5 and 4 keV is simulated within a Monte-Carlo frame work. The elastic scattering cross sections have been obtained from a modified Rutherford differential cross section, whereas inelastic core and valence electron excitation are calculated using the Gryzinski's expression. The dependence of the backscattering coefficient, mean implantation depth and stopping profiles on the angle of incidence has been examined. These quantities are found to be significantly enhanced as the angle of incidence becomes higher which is generally in consistent with previous simulations. [ABSTRACT FROM AUTHOR]

Based on a pseudopotential scheme, the composition dependence of energy band-gaps of zinc-blende Mg[sub x]Zn[sub 1-x]Se ternary alloys in the composition range of 0≤x≤1 are determined. The effect of deviation of lattice constants of the alloys of interest from Vegard's law on the optical bowing parameter and system transition between the direct and indirect structures is discussed. [ABSTRACT FROM AUTHOR]

Electron-positron momentum densities along different crystallographic directions and positron bulk lifetime in Si[sub 1-x]Ge[sub x] alloys have been investigated within the pseudopotential formalism employing the independent particle model. Special attention has been given to the effect of the deviation of the alloy lattice parameters from Vegard's rule on the studied quantities. It is found that using Vegard's law leads to an underestimation of the total positron annihilation rate indicating therefore an overestimation of the positron bulk lifetime. This result could not be checked using the Siethoff relation (H. Siethoff, Phys. Stat. Sol. B205, R3 (1998)). Moreover, this relation predicts a monotonic dependence of the positron bulk lifetime on the alloy composition which disagrees with the positron lifetime measurement. [ABSTRACT FROM AUTHOR]

The mean penetration depths and stopping profiles of positrons with incident energies up to 10 keV impinging on semi-infinite aluminum with normal and oblique angles of incidence are stochastically modelled within a Monte-Carlo framework. The elastic scattering cross sections have been obtained from a partial wave expansion. To model inelastic core and valence electron excitation, we have used the Gryzinski's expression. Our simulated results agree very well with the available experimental data and clearly demonstrate that the mean penetration depths are not adequately described by the simple power law commonly used in defect profiling. This suggests that both mean penetration depths and stopping profiles cannot generally be modelled by material-independent parameters as was proposed previously. The mean penetration depth decreases non-monotonically with increasing the angle of incidence from 0° to 80°. This can be seen from the reduction of the width of the implantation profiles. [ABSTRACT FROM AUTHOR]

Momentum densities of electron-positron pairs in cubic Ga[sub x]In[sub 1-x]As[sub y]Sb[sub 1-y] lattice matched to GaSb and InAs are studied for the first time to the best of our knowledge, with the aim of investigating the disorder and substrate effects on these quantities in the materials for interest. The electron wavefunction is calculated using the pseudopotential band model under the virtual crystal approximation with and without incorporating the effects of compositional variations. The calculations of the positron wavefunction is made in an identical manner, employing the point-core approximation for the ionic potential. It is found that while the electron-positron momentum densities in Ga[sub x]In[sub 1-x]As[sub y]Sb[sub 1-y] at x = 0.50 are sensitive to the compositional disorder, they are not altered by the change of substrate. [ABSTRACT FROM AUTHOR]