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A pseudopotential calculation of the electronic structure of AlGaSb ternary alloys in the zinc-blende structure has been performed. The compositional dependence of energy gaps, electron and heavy hole effective masses and ionicity of the material system of interest have been examined and discussed. Special attention has been given to the effect of the alloy disorder on the direct (-) bandgap energy. It is found that all features of interest vary monotonically with increasing the Al concentration . Besides, bandgap bowing parameters and extent of the direct-to-indirect bandgap transition have been determined. Our findings agree generally well with the data reported in the literature. Trends in ionicity are found to be consistent with the Phillips ionicity scale. [ABSTRACT FROM AUTHOR]

Based on the self-consistent ab initio full potential-linearized augmented plane wave method, the structural, electronic, optical, and thermodynamic properties of CdSeTe ternary semiconductor alloys have been investigated. The exchange-correlation potential was calculated using both the generalized gradient approximation (GGA) by Perdew-Burke-Ernzerhof (PBE) and the GGA by Engel-Vosko (EV-GGA). The ground-state properties are determined for the cubic bulk materials CdSe, CdTe, and their mixed crystals at various concentrations ( x = 0.25, 0.5, and 0.75). Deviation of the lattice parameter from Vegard's law and the bulk modulus from linear concentration dependence has been examined. The microscopic origins of the band-gap bowing parameter have been discussed. Moreover, the refractive index and the optical dielectric constant for CdSeTe are studied using different models. Besides, the thermodynamic stability of the alloys of interest is investigated by means of the miscibility critical temperature. [ABSTRACT FROM AUTHOR]

Using first principles total energy calculations within the full-potential linearized augmented plane wave method, we have studied the structural and electronic properties of yttrium nitride (YN) in the three phases, namely wurtzite, caesium chloride and rocksalt structures. The calculations are performed at zero and under hydrostatic pressure. In agreement with previous findings, it is found that the favored phase for YN is the rocksalt-like structure. We predict that at zero pressure YN in the rocksalt structure is a semiconductor with an indirect bandgap of 0.8 eV. A phase transition from a rocksalt to a caesium chloride structure is found to occur at ∼134 GPa. Besides, a transition from an indirect ( Γ− X) bandgap semiconductor to a direct ( X− X) one is predicted at pressure of ∼84 GPa. For the electron effective mass of rocksalt YN, these are the first results, to our knowledge. The information derived from the present study may be useful for the use of YN as an active layer in electronic devices such as diodes and transistors. [ABSTRACT FROM AUTHOR]

The structural parameters and hydrostatic pressure coefficients of CdSxTe1-x in the two phases, namely zinc-blende and NaCl as well as the transition pressures from zinc-blende to NaCl structures at various S concentrations are presented. The calculations are performed using the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT) in the local density approximation (LDA), and two developed refinements, namely the generalized gradient approximation (GGA) of Perdew et al. for the structural properties and Engel-Vosko for the band structure calculations. Detailed comparisons are made with published experimental and theoretical data and show generally good agreement. The present results regarding the studied quantities for compositions x in the 0–1 range (0 < x < 1) and for the NaCl phase are predictions and may serve as a reference for experimental work. [ABSTRACT FROM AUTHOR]

We present an investigation of the electronic properties and optical constants of zinc-blende ZnSxSe1-x semiconducting alloys at normal and under hydrostatic pressure up to 20 kbar. For this purpose, we used an empirical pseudopotential method within the virtual crystal approximation. The effects of alloy composition are taken into consideration in the calculation, which improves significantly the bandgap bowing parameters with respect to the experiment. Results regarding the composition and pressure dependences of energy bandgaps, electron valence and conduction charge distributions, optical high-frequency dielectric constant and its linear pressure coefficient are presented and discussed. The information derived from the present study may be useful for the development of opto-electronic devices that operate in the blue/green spectral range. [ABSTRACT FROM AUTHOR]

We present an investigation of the electronic properties and optical constants of zinc-blende ZnSxSe1-x semiconducting alloys at normal and under hydrostatic pressure up to 20 kbar. For this purpose, we used an empirical pseudopotential method within the virtual crystal approximation. The effects of alloy composition are taken into consideration in the calculation, which improves significantly the bandgap bowing parameters with respect to the experiment. Results regarding the composition and pressure dependences of energy bandgaps, electron valence and conduction charge distributions, optical high-frequency dielectric constant and its linear pressure coefficient are presented and discussed. The information derived from the present study may be useful for the development of opto-electronic devices that operate in the blue/green spectral range. [ABSTRACT FROM AUTHOR]

Based on the pseudopotential scheme under the virtual crystal approximation in which the effect of compositional disorder is involved, the dependence of optoelectronic properties of GaAs x Sb1- x on alloy composition x have been studied. Our results showed generally good agreement with the available experimental data. The material of interest is found to exhibit features of both direct and indirect band-gap semiconductor depending on the alloy composition x. The method used has been combined with the Harrison bond-orbital model and employed to calculate the dielectric constants and their composition dependence. [ABSTRACT FROM AUTHOR]

Abstract: A pseudopotential formalism within the virtual crystal approximation in which the effects of composition disorder are involved is applied to the Ga x In1−x As y P1−y quaternary alloys in conditions of lattice matching to GaAs, InP and ZnSe substrates so as to predict their energy band gaps. Very good agreement is obtained between the calculated values and the available experimental data for the alloy lattice matched to InP and GaAs. The alloy is found to be a direct-gap semiconductor for all compositions whatever the lattice matching to the substrates of interest. The band-gap ranges and the ionicity character are found to depend considerably on the particular lattice-matched substrates suggesting therefore that, for an appropriate choice of and the substrate, Ga x In1−x As y P1−y could provide more diverse opportunities to obtain desired band gaps, which opens up the possibility of discovering new electronic devices with special features and properties. [Copyright &y& Elsevier]

Abstract: Structural and electronic parameters of zincblende GaAs are obtained from density-functional-theory calculations utilizing an ab initio total energy pseudopotential technique within the local-density and the generalized gradient approximations. Detailed comparisons are made with the existing measured values and with results obtained in previous theoretical studies. The agreement between the present results and the available data from the literature is roughly satisfactory. Dependencies of some computed quantities on pressure are examined. [Copyright &y& Elsevier]

Based on a pseudopotential scheme, the composition dependence of energy band-gaps of zinc-blende Mg[sub x]Zn[sub 1-x]Se ternary alloys in the composition range of 0≤x≤1 are determined. The effect of deviation of lattice constants of the alloys of interest from Vegard's law on the optical bowing parameter and system transition between the direct and indirect structures is discussed. [ABSTRACT FROM AUTHOR]

The pseudopotential method within the virtual crystal approximation combined with the Harrison bond-orbital model were used to determine all three elastic constants, and hence Poisson''s ratio of GaxIn1−xSb semiconductor alloys. Our results for parent compounds are compared to experiment and other theoretical calculations and showed generally good agreement. The effect of compositional disorder on the studied quantities has been examined. We found an important bowing in all elastic constants and bulk modulus versus Ga content. The Poisson ratio was found to be independent of alloy composition x. [Copyright &y& Elsevier]

The positron states in the ternary alloys Ga1−xInxN in the zincblende structure in the range fromx= 0 tox= 1 have been investigated. The electron wavefunction is calculated using the pseudopotential band model within the virtual-crystal approximation. To make allowance for the compositional disorder, a correction to the alloy potential has been introduced. The positron wavefunction is evaluated under the point-core approximation for the ionic potential. The shapes of the profiles indicate that the integrated electron-positron momentum densities along different crystallographic directions become less flat in going from GaN to InN through the equimolar alloy Ga0.50In0.50N. Moreover, a nonlinear dependence of the positron bulk lifetime was found as the In concentration is increased. These results reflect the change of positron annihilation characteristics with the composition in III-V nitride semiconductor alloys. [ABSTRACT FROM PUBLISHER]

Highlights • Electron scattering in Si x Ge 1 − x and GaAs x N 1 − x targets. • Modeling of penetration range of electrons impinging on Si x Ge 1 − x and GaAs x N 1 − x targets. • Modeling of transport cross-sections of electrons in Si x Ge 1 − x and GaAs x N 1 − x targets. • Backscattering coefficient of electrons penetration in Si x Ge 1 − x and GaAs x N 1 − x targets. • Composition dependence of electron range and backscattering coefficient in Si x Ge 1 − x and GaAs x N 1 − x targets. Abstract The alloy composition dependence of penetration range and backscattering coefficient of electrons normally impinging on Si x Ge 1 − x and GaAs x N 1 − x semiconductor alloys targets for beam energies in the range 0.5–3.5 keV has been investigated. The electron penetration range is calculated using the Ashley's model. The electron backscattering coefficient is determined using both the Vicanek and Urbassek theory where the transport cross-sections are obtained more accurately via an improved approximation and Monte Carlo method in which the inelastic scattering processes are treated via Ashley's optical model. Our results regarding the electron backscattering coefficient for Si and Ge targets are found to be much higher than those of experiment when using the Vicanek and Urbassek theory. However, the use of Ashley's model via Monte Carlo method gives results that are in reasonably good accord with the experimental data reported in the literature in the low energy regime being considered here. [ABSTRACT FROM AUTHOR]

The electron and positron chemical potentials, positron affinity and bulk lifetime as well as the positronium work function in InP are investigated. The emphasis of this work is on the hydrostatic pressure effect on these features. The calculations are performed with a pseudopotential approach and the independent particle model. All parameters of interest are found to vary monotonically with pressure. Our findings showed that under compression the positron annihilates differently in InP semiconductor compound. At zero pressure, the positron bulk lifetime is calculated to be 243.47 ps. However, upon compression it decreases almost linearly suggesting the decrease of the crystal ionicity under applied pressure. The positronium work function is found to increase with raising pressure which indicates that under compression less positronium atoms will be formed in InP sample surface and ejected into the vacuum. The parameters investigated in the present work are important in slow-positron-beam experiments. [ABSTRACT FROM AUTHOR]

The dependence on hydrostatic pressure of the electronic and optical properties of zinc-blende AlSb semiconducting material in the pressure range of 0–20 kbar has been reported using a pseudopotential approach. At zero pressure, our findings showed that the electron and heavy hole effective masses are 0.11 and 0.38 m 0 , respectively. Moreover, our results yielded values of 3.3289 and 11.08 for refractive index and high frequency dielectric constant, respectively. These results are found to be in good accord with experiment. Upon compression, all physical parameters of interest showed a monotonic behavior. The pressure-induced energy shifts for the optical transition related to band-gaps indicated that AlSb remains an indirect (Г-X) band-gap semiconductor at pressures from 0 to 20 kbar. The trend in all features of interest versus pressure has been presented and discussed. It is found that the lattice parameter is reduced from 0.61355 to 0.60705 nm when pressure is raised from 0 to 20 kbar. The present investigation may be useful for mid-infrared lasers applications, detectors and communication devices. [ABSTRACT FROM AUTHOR]

Abstract: The effect of pressure on optical phonons and polaron properties in ZnS, ZnSe, and ZnTe II–VI compound semiconductors has been investigated. The calculations are performed in the framework of ab initio pseudopotential approach based on the density functional perturbation theory. At zero pressure, a reasonable degree of agreement is generally found between our results and data available in the literature. It is found that when pressure is increased the phonon modes at Г in the Brillouin zone are shifted towards high energies. The pressure dependence of features such as Fröhlich coupling parameter, the Debye temperature of the longitudinal optical phonon frequency and the polaron effective mass showed that the polaron properties are sensitive to the pressure effect. [Copyright &y& Elsevier]

Based on the pseudopotential scheme, the hydrostatic pressure dependence of the electronic properties has been predicted for zinc-blende ZnS. The material of interest is found to exhibit features of both direct and indirect band-gap semiconductor depending on the applied pressure. Detailed plots of the valence charge distribution along the [1 1 1] direction and in the (1 1 0) plane at different pressures are also presented and discussed. [Copyright &y& Elsevier]

The band structures of some zincblende III–V semiconductor alloys are calculated beyond the virtual crystal approximation (VCA) using the empirical pseudopotential method (EPM). Our results show that the calculated optical bandgap bowing parameter agree with the experiment only when going beyond the VCA. We also found that the direct bandgap (Γ→Γ) bowing factor becomes generally larger on going from alloys with small lattice mismatches to those with larger ones. [Copyright &y& Elsevier]

In order to expand the scope of application of ternary nitrides and explore more thoroughly their potential as novel materials, ab initio calculations founded on density functional theory are executed to examine the mechanical, electronic, optical and transport properties of Ca 5 Si 2 N 6 and Sr 5 Ge 2 N 6 nitrides. These compounds are thermodynamically stable established on coherent energy and enthalpy of formation, with Ca 5 Si 2 N 6 having the best stability. The estimated values of elastic constants and their derived properties suggest that the items under examination are mechanically stable, ductile and elastically anisotropic. Electronic properties have been evaluated using the GGA and TB-mBJ exchange-correlation potentials. The band structure calculated via TB-mBJ reveals that these nitrides are semiconductors, where Ca 5 Si 2 N 6 has a direct energy gap of 3.55 eV and Sr 5 Ge 2 N 6 an indirect band-gap of 3.15 eV. By combining Debye temperature and band-gap values, it was concluded that the nitridosilicate compound can be used as phosphor material. According to the optical response, which was examined in terms of dielectric function, complex refractive index, absorption, reflectivity and energy damage function, the potential applications of Ca 5 Si 2 N 6 and Sr 5 Ge 2 N 6 have been discussed. Further, thermoelectric properties are computed utilizing the semi-classical Boltzmann transport notion. The obtained results show a large strength operator and depressed thermal conductivity driving to rising figure of merit values, particularly at 300 K (0.978–0.986), signifying that the studied ternary nitrides are favorable nominees for thermoelectric employments at both low and room temperatures. • The calculated elastic constants suggest that Ca 5 Si 2 N 6 and Sr 5 Ge 2 N 6 nitrides are mechanically stable, ductile and elastically anisotropic. • The calculated band structure shows that Ca 5 Si 2 N 6 has a direct gap of 3.55 eV whereas Sr 5 Ge 2 N 6 is an indirect gap of 3.15 eV. • The combination of Debye temperature and band-gap values, showed that the nitridosilicate compound can be used as phosphor material. • The optical response has permitted the discussion on the potential applications of Ca 5 Si 2 N 6 and Sr 5 Ge 2 N 6 materials. • The nitrides Ca 5 Si 2 N 6 and Sr 5 Ge 2 N 6 are found to be favorable nominees for thermoelectric employments at both low and room temperatures. [ABSTRACT FROM AUTHOR]

• Structural parameters of Sr 3 MgGeN 4 and Ba 3 GeMgN 4 show that both crystals are energetically stable. • The obtained elastic properties of Sr 3 MgGeN 4 and Ba 3 GeMgN 4 are strongly pressure dependent. • An analysis of electronic band structures shows that Sr 3 MgGeN 4 (Ba 3 GeMgN 4) is a semiconductor with a direct (indirect) band gap of 1.476 eV (1.194 eV). • The chemical bonding in both semiconductors Sr 3 MgGeN 4 and Ba 3 GeMgN 4 is dominated by a covalent character. • Based on the absorptive and PDOS curves, possible inter-band transition from filled VB to empty CB states could be related to electron transitions. The electronic structure, optical and thermodynamic properties of M 3 GeMgN 4 (M = Sr or Ba) nitrides have been investigated using first-principles calculations. The calculated equilibrium lattice parameters and inter-atomic bond-lengths show excellent concordance with experiment. The elastic constants (C ij s) and their derived properties have been calculated showing that the examined compounds are mechanically stable and elastically soft, ductile and anisotropic. The analysis of the electronic structure reveals a semiconductor comportment for both crystals. The Sr 3 GeMgN 4 (Ba 3 GeMgN 4) compound possesses a direct (indirect) energy gap of 1.476 eV (1.194 eV). The chemical bonding in both semiconductors is dominated by a covalent character, which originates from the Ge-N and Mg-N hybridized states. Both nitrides show moderate dielectric properties, high visible and UV absorbance, indicating that both materials are suitable for optoelectronic applications. Phononic dispersion curves have demonstrated the dynamical stability of the studied crystals. [ABSTRACT FROM AUTHOR]

The elastic properties and optical spectra are studied for zinc-blende ZnS 1−x O x dilute semiconductor alloys in the generalized gradient approximation of the density-functional formalism. The calculations are performed with the full potential linearized augmented plane wave method. The emphasis of this work is on the effect of low oxygen concentration on the studied properties. The theoretical results are compared to values extracted from experiments and showed generally good agreement. The investigated properties are found to be affected by adding only a small amount of oxygen atoms to ZnS. The present study may be useful for photovoltaic materials for solar cells. [ABSTRACT FROM AUTHOR]

Using the pseudopotential approach, we have undertaken a detailed study of the energy levels and optical properties of zinc-blende GaN spherical quantum dots as a function of their radius taken in the range 1–10 nm. Features such as energy levels, energy band gaps, electron and heavy hole effective masses, refractive index, dielectric constants and transverse effective charge have been investigated. The quantum confinement is found to be of major effect on all the studied quantities for quantum dot radius below 5 nm. Beyond 5 nm, all properties of interest tend towards retrieving the bulk properties. [ABSTRACT FROM AUTHOR]