Rezek Mohammad

THE ELECTRONIC BAND STRUCTURE OF AlN, AlSb, AlAs AND THEIR TERNARY ALLOYS WITH In

The electronic band structure of AlN, AlSb, AlAs and their ternary alloys with In has been investigated by ETB. The ETB method has been formulated for sp3d2 basis and nearest neighbor interactions of the compounds and its energy parameters have been derived from the results of the present first principles calculations carried on AlN, AlSb and AlAs. It has been found that the present ETB energy parameters can produce the band structure of the compounds and their ternary alloys with In successfully.

First-principles calculations for the structural and electronic properties of GaAs1−xPx nanowires

Structural stability and electronic properties of GaAs1−xPx (0.0≤x≤1.0) nanowires (NWs) in zinc-blende (ZB) (∼5≤ diameter ≤∼21A) and wurtzite (WZ) (∼5≤diameter≤∼29A) phases are investigated by first-principles calculations based on density functional theory (DFT). GaAs (x=0.0) and GaP (x=1.0) compound NWs in WZ phase are found energetically more stable than in ZB structural ones. In the case of GaAs1−xPx alloy NWs, the energetically favorable phase is found size and composition dependent. All the presented NWs have semiconductor characteristics. The quantum size effect is clearly demonstrated for all GaAs1−xPx (0.0≤x≤1.0) NWs. The band gaps of ZB and WZ structural GaAs compound NWs with ∼10≤ diameter ≤∼21A and ∼5≤diameter≤∼29A, respectively are enlarged by the addition of concentrations of phosphorus for obtaining GaAs1−xPx NWs proportional to the x values around 0.25, 0.50 and 0.75.

FIRST-PRINCIPLES CALCULATIONS FOR THE STRUCTURAL AND ELECTRONIC PROPERTIES OF ScxAl1-xN ALLOYS

The first-principles calculations based on Density Functional Theory (DFT) within generalized gradient approximation (GGA) of Engel–Vosko–Perdew–Wang and modified exact exchange potential of Becke–Johnson have been introduced for the structural and electronic properties of the ScxAl1-xN alloys, respectively. The present lattice constants calculated for the ScAlN alloys and the end compounds (AlN and ScN) are found to be in very good agreement with the available experimental and theoretical ones. The stable ground state structures of the ScxAl1-xN alloys are determined to be wurtzite for the Sc concentration less than ~0.403 and rock-salt for the higher Sc concentrations. The present electronic band structure calculations within Becke–Johnson scheme are found to be capable of providing energy band gaps of the AlN and ScN compounds very close to the ones of the available experiments and expensive calculations. According to the calculations of Becke–Johnson potential, the ScxAl1-xN alloys in the wurtzite and zinc-blende structures are direct band gap materials for the Sc concentrations in the ranges of (0.056 ≤ x ≤ 0.833) and (0.03125 ≤ x ≤ 0.0625, 0.375 ≤ x ≤ 0.96875), respectively. However, the ScAlN alloys in the rock-salt phase are determined to be direct band gap materials for total range of the Sc concentration considered in this work. While the energy gaps of the RS-AlScN alloys are found to be extending from near ultraviolet to near infrared with a large (negative) bowing, the ones of the WZ-AlScN and ZB-AlScN alloys are determined to be varying in a small energy range around near ultraviolet with a small (negative) bowing.

THE ELECTRONIC BAND STRUCTURE OF GaN, GaAs AND InxGa1-xAs1-yNy ALLOYS

The electronic band structure of GaN and GaAs has been investigated by ETB to obtain the band gap bowing of InxGa1-xAs1-yNy alloys lattice matched to GaAs. The ETB method has been formulated for sp3d2 basis and nearest neighbor interactions of the compounds, and its energy parameters have been derived from the results of the present first principles calculations carried out on GaN and GaAs. It has been found that the present ETB energy parameters are capable of producing the electronic band structure of corresponding compounds and the large bowing parameter of InGaAsN alloy.

First-principles calculations for mechanical and electronic features of strained GaP nanowires

The mechanical and electronic properties of GaP nanowires are investigated by computing the Young’s modulus, Poisson’s ratio, energy band gap and effective carrier masses using first-principles calculations based on density functional theory. The wurtzite structural nanowires with diameters upper limited to ∼27A are strained by uniaxial strains in the range of −7.5–7.5%. The Young’s moduli of nanowires are found to be decreased with increase of the size in the direction of the Young’s modulus of the bulk GaP. The Poisson’s effect is determined to be stronger in GaP nanowires than in the bulk. The energy band gaps of the unstrained and strained nanowires are obtained to be enlarged with decrease of the size due to the quantum size effect. The confinement effect is found larger in the compressed nanowires than in the stretched ones. All the unstrained nanowires except the largest one are indirect band gap materials. Indirect to direct band gap transition is determined to be size and strain dependent. The effective carrier masses in all unstrained nanowires are found small compared to the ones in the bulk GaP. The effective electron and hole masses are obtained to be modulated in nanowires of this work by the compressive and both compressive/tensile strains, respectively.

THE STRUCTURAL AND ELECTRONIC PROPERTIES OF BNxAs1-x ALLOYS

The structural and electronic properties of BNxAs1-x alloys have been investigated in the total range of nitrogen by the FP-LAPW method based on DFT within the EV-PW-GGA scheme. The equilibrium lattice constants, bulk moduli, first-order pressure derivatives of the bulk moduli, and cohesive energies have been obtained by total energy calculations of the alloys after both volume and geometry optimizations. The large bowing parameters found for the lattice constants and bulk moduli have demonstrated that the validity of Vegards linear rule in the definitions of these structural features of the BNxAs1-x alloys is broken. The energy bands and the effective masses of the alloys have been calculated as a function of nitrogen concentration. The large bowing displayed by the variation of the energy gaps has indicated the band gap engineering capacity of the BNxAs1-x alloys and again in deviations from Vegards linear rule. The effective electron masses calculated either at the edges of the conduction bands or along the directions approaching the edges of the conduction bands are all found to be small with respect to the effective electron masses in the BAs and BN compounds calculated at the Δmin and X points, respectively.