B. Bouhafs

FP-LAPW investigations of electronic structure and bonding mechanism of NbC and NbN compounds

We have studied the structural and electronic properties of niobium nitride and niobium carbide by means of accurate first principle total energy calculations using the full-potential linearized augmented plane wave method. The calculations are based on density functional theory and we have used the local density approximation as well as the generalized gradient approximation for the exchange and correlation potential. We obtained reasonable results comparatively with the experimental data and other calculations.

Molecular-dynamics simulation of structural and thermodynamic properties of boron nitride

Structural and thermodynamic properties of cubic boron nitride (c-BN) under pressure and for varying temperature are studied by molecular-dynamics (MD) simulation with the use of a well-tested Tersoff potential. Various physical quantities including the thermal expansion coefficient and heat capacity are predicted. Our simulation is extended to study liquid boron nitride at various densities.

Trends in band-gap pressure coefficients in boron compounds BP, BAs, and BSb

We have performed an ab initio investigation for a series of boron compounds, BP, BAs, and BSb, and have compared their structural and electronic properties with those of c-BN. The calculations are performed using a plane-wave expansion within the local density approximation and the pseudopotential approximation. Results are given for lattice constants, bulk moduli, band structures, and band-gap pressure coefficients. The electronic properties of these compounds are shown to have features that differ from those of other III-V materials. We found that the direct-band-gap pressure coefficient in boron compounds is nearly independent of the anion substitutions. As a result, this trend is similar to the one resulting from cation substitutions in other zinc-blende compounds. This is another anomalous behaviour which can be characterized by reversing the standard assignments for the anion and cation in these compounds.

First-principles study of structural and electronic properties of BSb

We have performed the first ab initio investigation of the boron compound BSb with zinc-blende structure, and have compared its structural and electronic properties with those of other boron compounds such as BN, BP, and BAs. The calculations are performed using a plane-wave expansion within the local density approximation and the pseudopotential approximation. Results are given for the lattice constant, bulk modulus, band structure, and total valence charge density. The electronic band structure of BSb proved to have features that differ from those of other III-V materials. It is found that BSb is less ionic than other III-V compounds, with an indirect band gap, and presents the same anomalous behaviour as BP and BAs.

Calculation of structural, optical and electronic properties of ZnS, ZnSe, MgS, MgSe and their quaternary alloy Mg1−xZnxSySe1−y

Abstract The structural and electronic properties of the binary semiconductor compounds ZnS, ZnSe, MgS and MgSe in the cubic structure are calculated using the self-consistent scalar-relativistic full potential linear-augmented plane wave method (FP-LAPW) within the local (spin) density approximation (LSDA). From the calculated values of the band-gap energy we have determined the electronic and optical properties of quaternary alloys Mg1−xZnxSySe1−y using the simple tight-binding sp3s* theory, which incorporates compositional disorder as an effective potential. In addition, the refractive index of MgS, MgSe, ZnS and ZnSe was computed using both real and imaginary parts of the dielectric function. The result indicates that the refractive index increases with allowing for the Mg1−xZnxSySe1−y lattice matched to GaAs.

Competition between the ionic and covalent character in the series of boron compounds BP, BAs, and BSb

We present first-principles calculations of the bonding properties for the series of boron compounds BP, BAs, and BSb. The plane-wave pseudopotential approach to density functional theory in the local density approximation has been used to calculate the equilibrium properties, i.e., the ground-state energy, the lattice constant, the bulk modulus, its pressure derivative, and the ionicity factor. The valence electron density is used to study the modification of the bonding with respect to different pressures. The calculated electronic charge densities present an anomalous behaviour which can be characterized by reversing the standard assignments for the anion and cation in these compounds. The competition between the ionic and the covalent character in these materials is discussed in relation to the charge transfer. Estimates of the ionicity and its pressure derivative for the series of boron compounds are presented. The distribution of the valence charge density suggests that the bonding in these materials is less ionic than in other zinc-blende compounds.

ELECTRONIC AND OPTICAL PROPERTIES OF COPPER HALIDES MIXED CRYSTAL CUCL1-XIX

Abstract The effects of chemical disorder on the electronic and optical properties of mixed CuCl 1− x I x crystals are studied on the basis of a modified virtual crystal approximation, which incorporates compositional disorder as an effective potential. We use a simple tight-binding (TB) theory including d electron orbitals on the cation site. We show that such an approach provides analytical results for calculating energy gaps and bowing parameters. The band structures of CuCl and CuI are discussed. The variation of the energy with alloy concentration in the pseudo-binary system formed with these compounds is reported and interpreted. The essential features of disorder-induced changes in electronic and optical structure are exhibited from the TB results by two characterization parameters: the subband energy spacings, and the density of states

First‐Principles Calculations of Optical Properties of AlN, GaN, and InN Compounds under Hydrostatic Pressure

We present first-principles full-potential linearized augmented plane wave calculations of the effect of hydrostatic pressure on the optical properties of wurtzite GaN, InN and AIN compounds. The refractive index and its variation with hydrostatic pressure are well described. The accurate calculation of linear optical function (refraction index and its pressure derivative, and both imaginary and real parts of dielectric function) is performed in the photon energy range up to 30 eV. The predicted optical constant agrees well with the available experimental data.

Energy band structure calculation of GexSn1−x and SixSn1−x alloys

Starting from band structures of the constituent materials, the electronic band structure of the semiconducting alloys GexSn1−x and SixSn1−x are calculated by the empirical pseudopotential method using a corrected virtual crystal approximation (VCA) which incorporates compositional disorder as an effective potential. Various quantities, including the bowing parameter of the fundamental band gap, the energies of several optical gaps, and the crossover of the band gaps are predicted.

Theoretical analysis of disorder effects on electronic and optical properties in InGaAsP quaternary alloy

The effects of structural and chemical disorder on electronic and optical properties of InGaAsP quaternary alloy are studied on the basis of a modified virtual crystal approximation calculated within a simple tight-binding sp3s* theory, which incorporates compositional disorder as an effective potential. Using a minimal set of fitting parameters, we show that such an approach provides analytical results for calculating energy gaps and bowing parameters. We show that the calculated bowing parameter agrees reasonably well with experimental data. The essential features of structure and disorder-induced changes in electronic and optical structure are exhibited in the sp3s* results by two characterization parameters: the subband energy spacings, and the density of states. The changes in each of them are found to depend on the interrelated trends of structure and disorder effects.