Ali Zaoui

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.

Optical properties of SiSn and GeSn

The purpose of this study is to understand the trends in optical properties of group-IV materials, especially SiSn and GeSn. Here we attempt to provide a theoretical base for further studies of these materials in zinc-blende structures. There is no experimental data for the optical properties. Nevertheless, an analysis of the theoretical structure can be useful.

Magnetic trends in GaxMn1-xN, AlxMn1-xN, and InxMn1-xN ternary systems: A first-principles study

We have performed first-principles calculations using the full-potential linearized augmented plane-wave method to investigate the magnetic properties of Al1−xMnxN, Ga1−xMnxN, and In1−xMnxN semiconductors, for x=0.25, 0.50, and 0.75 in their ordered zinc-blend ferromagnetic phase. For the structural properties, we found strong positive deviation from Vegard’s law regarding the variation in the lattice parameter which is in direct contrast with conventional III-V alloys. In addition, we found that In1−xMnxN exhibits a half-metallic characteristic for all Mn composition. A total magnetic moment of 4 μB was found for all In1−xMnxN compositions, and for half-metallic phases of Al1−xMnxN and Ga1−xMnxN, respectively. The Mn atom is the main source of the total magnetic moment in these alloys, while the contributions from Al, Ga, In, and N are negligible.

First principles calculations for dilute InAs1−xNx alloys

Dilute nitrides such as InAsN alloys represent a new class of highly mismatched semiconductors alloys, which have recently attracted strong attention due to their unique physical properties. In this paper we present computed structural, thermodynamic, and energetic characteristics of the dilute InAsN alloys. We found strong deviations from Vegards law for the variation of the lattice constant of InAsN. Regarding the local environment of N, we notice that the clustering has a weak influence on the In-As bond, but shortens the In-N bond and strongly reduces the energy band gaps. In addition, wide miscibility gaps are predicted in the temperature range relevant to specimen synthesis and processing.

Band-gap bowing in SixGe1-x alloy

Abstract The alloy SiGe exhibits smallest observed optical bowing. A theoretical analysis of this effect by use of self-consistent ab initio pseudopotential technique for ordered 50–50% alloy in the zinc-blende structure predicted correct optical bowing and revealed that both chemical and structural effects are important for this compound.

Micromechanical Modeling of the Effective Viscoelastic Response of Polyamide-6-Based Nanocomposites Reinforced with Modified and Unmodified Montmorillonite Clay

A micromechanics-based approach using a self-consistent scheme based on the double-inclusion model is adopted to develop a pertinent model for describing the viscoelastic response of polymer/clay nanocomposites. The relationship between the intercalated nanostructure and the effective nanocomposite stiffness is constructed using an equivalent stiffness method in which the clay stacks are replaced by homogeneous nanoparticles with predetermined equivalent anisotropic stiffness. The capabilities of the proposed micromechanics-based model are checked by comparing with the experimental viscoelastic (glassy to rubbery) response of two polyamide-6-based nanocomposite systems reinforced with a modified montmorillonite clay (Cloisite 30B) and an unmodified sodium montmorillonite clay (Cloisite Na+), favoring, respectively, exfoliation and intercalation states.

Dynamic properties of III–V polytypes from density-functional theory

The recently discovered hexagonal wurtzite phase of several III–V nanowires opens up strong opportunity to engineer optoelectronic and transport properties of III–V materials. Herein, we explore the dynamical and dielectric properties of cubic (3C) and wurtzite (2H) III–V compounds (AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, and InSb). For cubic III–V compounds, our calculated phonon frequencies agree well with neutron diffraction and Raman-scattering measurements. In the case of 2H III–V materials, our calculated phonon modes at the zone-center Γ point are in distinguished agreement with available Raman-spectroscopy measurements of wurtzite GaAs, InP, GaP, and InAs nanowires. Particularly, the “fingerprint” of the wurtzite phase, which is our predicted E2(high) phonon mode, at 261 cm−1(GaAs), 308 cm−1(InP), 358 cm−1(GaP), and 214 cm−1(InAs) matches perfectly the respective Raman values of 258 cm−1, 306.4 cm−1, 353 cm−1, and 213.7 cm−1 for GaAs, InP, GaP, and InAs. Moreover, the dynamic charges and high...

Revealing strong polytypism tendency in MgTe from first-principles

The search for stable polytype phases of III-V and II-VI materials has attracted great interest in recent years due to their great potential for a broad range of applications. Here using density functional theory, we systematically explore electronic structure properties of cubic (3C) and hexagonal (2H, 4H and 6H) polytypes of magnesium telluride: MgTe. Total energies and nearest-neighbor bilayer interaction energies evidence that MgTe shows a high propensity to polytypism. This finding is further supported by mechanical and phonon stabilities of all polytype phases of MgTe. Additionally, ground structural properties, energetic stability, mechanical properties, band structure energies, and dynamical properties are examined in relation with the stacking sequence of 3C, 2H, 4H, and 6H polytypes in the Mg-Te system.