Noureddine Amrane

Theoretical Studies of Positron Annihilation in Aluminum Bismuth Alloy

Electron and positron charge densities are calculated as a function of position in the unit cell for Aluminum Bismuth binary compound. Wave functions are derived from pseudopotential band structure calculations and the independent particle approximation (IPM), respectively, for the electrons and the positrons. It is observed that the positron density is maximum in the open interstices and is excluded not only, from the ion cores but also to a considerable degree from the valence bonds. Electron-positron momentum densities are calculated for (001, 110) planes. The results are used to analyze the positron effects in AlBi.

Pressure Effect on the Electronic Properties of Cerium Monochalcogenides CeX (X=S, Se, Te) Using Modified Becke-Johnson Exchange Potential and LDA+U

We present a systematic and comparative study of the electronic properties of CeX monochalcogenides, The density of state (DOS) and electronic band structure of CeX (X=S, Se, Te) have been calculated using the full-potential linearized augmented plane-wave (FP-LAPW) + local orbital (lo) method based on the density functional theory (DFT), which is implemented in WIEN2k code. The trends in the high pressure behavior of these systems are discussed. Four approximations for the exchange-correlation functional have been used, the GGAs of Perdew-Burke-Ernzherhof. (PBE08) , Engel-Vosko (EV93), a modified version of the exchange potential proposed by Becke and Johnson (MBJ), and LDA+U is used to calculate the band gaps at different pressures. All methods allow for a description of the Ce f electrons as either localized or delocalized, it is found that the underestimations of the bandgap by means of LDA-GGA and Engel-Vosko are considerably improved by using the modified Becke-Johnson (MBJ) potential for all compounds in the series, On the other hand, LDA+U, method gives good results for the lighter chalcogenides, but it fails to give good results for the heavier cerium monochalcogenides.

First principles calculations on the electronic properties of the II-VII semiconductors, radiation detectors, TlBr and TlCl

In this work, we have investigated the electronic properties of the III-VII binary compound semiconductors TiBr and TICI by means of first-principles density-functional total-energy calculation using the all-electron full potential linear augmented plane-wave method (FP-LAPW). The (FPLAPW) method was used within the density functional theory (DFT) along with the Engel-Vosko and (GGA96) exchange correlation potential. The energy bands along high symmetry directions, the density of states and valence charge density distributions cut through various planes are presented. The results have been discussed in terms of previously existing experimental and theoretical data, and comparisons with similar compounds have been made. Analysis of band structure suggests a direct and a pseudo-direct band gaps for both compounds.

ELECTRONEGATIVITY EFFECTS ON THE BANDGAP BOWING CHARACTERS IN COMPOUND-SEMICONDUCTOR TERNARY ALLOYS

We present a theoretical investigation of the existence and origins of the bandgap bowing character in compound semiconductor alloys based on both the sp3s*-tight-binding (TB) method, which includes the spin–orbit coupling, and the first-principle Full-Potential Linear Augmented Plane Wave (FP-LAPW) technique. First, we compare the bandgap variation versus composition in the III–V direct-bandgap-GaAs-based ternary alloys, namely between the common-cation GaSbxAs1-x and the common-anion Ga1-xInxAs ternary alloys. The results show that the bowing behavior exists only in the common-cation (i.e., GaSbAs) alloys as a result of an existing competition between the anion atoms (Sb and As) in trapping the electronic charge. The bowing parameter is found to be proportional to the electronegativity characters of the competing anions (i.e., χanion). The lack of such competition, in the case of common-anion alloys (i.e., GaInAs), makes the bowing be just absent and the variation of the bandgap become close to linear. ...