M. Ferhat

Magnetism and band gap narrowing in Cu-doped ZnO

First-principles calculations based on density functional theory are performed to study the magnetic, electronic, and optical properties of ZnO doped with 6.25%, 12.5%, and 18.75% of Cu. The Cu dopants are found spin polarized, and a net magnetic moment of 0.57μB is found for Cu at a composition of 6.25%. The calculations confirm an appreciable band gap reduction in ZnO in agreement with recent experimental results. The analysis of the partial density of states reveals that ferromagnetism and narrowing of ZnO band gap are due principally to the strong p-d mixing of O and Cu.

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.

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.

Giant and composition-dependent optical band gap bowing in dilute GaSb1−xNx alloys

Ab initio pseudopotential plane wave calculations and large 64-atom relaxed supercells are used to investigate the structural and electronic properties of GaNxSb1−x dilute alloys. While the band gaps of conventional III-V semiconductors have a simple and weak dependence on composition, this work illustrate a violation of this expected behavior. We show that the band gap decreases rapidly with increasing compositions of N and that GaNxSb1−x show an abnormal giant gap reduction. As a consequence, the optical band gap bowing is found to be giant and composition dependent as found for other mixed anion III-V–N systems.

APPLICABILITY OF THE EMPIRICAL PSEUDOPOTENTIAL METHOD TO SEMICONDUCTORS WITH D VALENCE ELECTRONS

Abstract We use the empirical pseudopotential method to calculate the band structure and the density of states of materials with d valence electrons. We choose for this calculation a prototype of the I–VII semiconductors family: the copper chloride CuCl. The problematic d levels are avoided by developing the wave function in a high number of plane waves and using a strong nonlocal pseudopotential. The results are in good agreement with previous calculations and experimental data and show that the use of pseudopotentials is possible for the calculation of the band structures and related physical properties.

Structural stability of thallium–V compounds

We have performed ab initio self-consistent calculations in order to investigate the structural stability of the thallium–V compounds: TlN, TlP, TlAs, TlSb and TlBi. Total energy calculations of several phases are considered here in order to fix the most stable structure for each compound. For the structures considered, the wurtzite one is found to be the ground state phase for TlN, the zinc-blende phase that for TlP and TlAs, while TlSb and TlBi favour the tetragonal PbO phase. Some unusual features, compared with the other III–V families, are registered for the systems studied, which we attempt to analyse and to explain in detail in the present paper.

Lattice dynamics study of bismuth III–V compounds

We present first-principles calculations of the structural and lattice-dynamical properties for cubic bismuth III-V compounds: BBi, AlBi and GaBi. The ground-state properties, i.e., the lattice constant and the bulk modulus, are calculated using a plane wave pseudopotential method within density functional theory. A linear-response approach to density functional theory is used to derive the phonon frequencies. The effect of pressure on the dynamical charges and the longitudinal optical-transverse optical splitting is also examined.

Magnetic properties of (ZnO)1/(CuO)1 (001) superlattice

The magnetic properties of (ZnO)1/(CuO)1 (001) superlattice have been investigated by means of ab initio calculations based on spin density functional theory. The ZnO/CuO superlattice is found to be spin polarized, and the calculated band structure suggests a 100% polarization of the conduction carriers. The analysis of the partial density of states reveals that ferromagnetism can be explained here by the strong p-d hybridization of O and Cu.

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.

Magnetism and clustering in Cr-doped InN

Density functional theory was applied to study the electronic and magnetic coupling of Cr-doped InN, in which magnetic configurations have been investigated. We found that the calculated ferromagnetic stabilizing energy is strongly linked to the Cr–Cr distance. The local magnetic moment of Cr is 2.3μB, and it weakly depends on the Cr–Cr distance. The coupling between the Cr d and the N p states is found to be the origin of ferromagnetism in the InCrN system. The generalized gradient approximation-1/2 correction procedure increases the polarization of InCrN, making this system a robust half-metallic ferromagnetic alloy.