First principles calculation of electronic properties and effective mass of zinc-blende GaN

Based on the first principle pseudopotential plane wave method, the electronic structure of zinc-blende semiconductor GaN is calculated. Using the relativistic treatment of valence states, the spin orbit splitting energy of valence band top near the center of Brillouin region is calculated. Based on the effective mass approximation theory, the effective mass of electrons near the bottom of the conduction band and the effective mass of light and heavy holes near the Γ point along the directions of [100], [110] and [111] are calculated. These parameters are valuable and important parameters of optoelectronic materials.

Energy-Band Theory

Various methods to calculate energy bands and the electronic structure of solids are described in detail. Although the emphasis lies on linear methods well known for their transparency and high numerical speed, traditional methods are described to supply historical background and to point the way to modern methods. After introducing Bloch electrons and the reciprocal space, plane waves, orthogonalized plane waves, and pseudopotentials are discussed, followed by the important augmented plane wave method (APW). Multiple scattering theory defines scattering phase shifts encoding atomic properties and the structure constants that describe the crystal lattice. Linear combination of atomic orbitals (LCAO) and linear combination of muffin-tin orbitals (LMTO) result in efficient and fast methods as does the related augmented spherical waves (ASW) method. The treatment of arbitrary spin configurations using the ASW method and the formulation of incommensurate spiral structures on the basis of the unitary SU(2) group are developed in detail.

Structural, electronic, optical and thermoelectric analysis of Rb/Cs2TeBr6 Vacancy ordered double perovskites

It is compulsory to develop technologies able to generate energy at negligible cost to the environment. Therefore, in present work, lead free vacancy ordered double perovskites Rb/Cs2TeBr6 were reported as green energy materials on basis of full potential linearized augmented plane wave method calculations. The study has been carried out in terms of structural, electronic, optical and thermoelectric properties. It was noted from values of tolerance factor and formation energy that both Rb/Cs2TeBr6 compounds are stable in perovskite structure. The band gaps were calculated in close resemblance with experiments. These values (2.09 eV Rb2TeBr6 and 2.10 eV for Cs2TeBr6 with EV-GGA) were examined in visible range of electromagnetic spectrum. The optical properties such as real and imaginary parts of dielectric function, optical conductivity and reflectivity ensured the use of Rb/Cs2TeBr6 compounds for solar cell applications. Also, the reasonable values of Seebeck coefficients and figure of merit proposed the studied compounds for thermoelectric power generation.

An ab initio study of structural, elastic and electronic properties of hexagonal MAuGe (M = Lu, Sc) compounds

In this paper, we performed a detailed theoretical study of structural, elastic and electronic properties of two germanides LuAuGe and ScAuGe by means of first-principles calculations using the pseudopotential plane-wave method within the generalized gradient approximation. The crystal lattice parameters and the internal coordinates are in good agreement with the existing experimental and theoretical reports, which proves the reliability of the applied theoretical method. The hydrostatic pressure effect on the structural parameters is shown. The monocrystalline elastic constants were calculated using the stress-strain technique. The calculated elastic constants of the MAuGe (M = Lu, Sc) compounds meet the mechanical stability criteria for hexagonal crystals and these constants were used to analyze the elastic anisotropy of the MAuGe compounds through three different indices. Polycrystalline isotropic elastic moduli, namely bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and the related properties are also estimated using Voigt-Reuss-Hill approximations. Finally, we studied the electronic properties of the considered compounds by calculating their band structures, their densities of states and their electron density distributions.

Voltage controlled on-demand magnonic nanochannels

Development of energy-efficient on-demand magnonic nanochannels (MNCs) can revolutionize on-chip data communication and processing. We have developed a dynamic MNC array by periodically tailoring perpendicular magnetic anisotropy using the electric field. Brillouin light scattering spectroscopy is used to probe the spin wave (SW) dispersion of MNCs formed by applying a static electric field at the CoFeB/MgO interface through the one-dimensional stripe-like array of indium tin oxide electrodes placed on top of Ta/CoFeB/MgO/Al2O3 heterostructures. Magnonic bands, consisting of two SW frequency modes, appear with a bandgap under the application of moderate gate voltage, which can be switched off by withdrawing the voltage. The experimental results are reproduced by plane wave method–based numerical calculations, and simulated SW mode profiles show propagating SWs through nanochannels with different magnetic properties. The anticrossing between these two modes gives rise to the observed magnonic bandgap.

The impurity states in different shaped quantum wells under applied electric field

In this paper, the impurity states in square, parabolic and V-shaped quantum wells (QWs) are calculated by the plane wave method under the theoretical framework of effective mass envelope function approximation. In different shaped QWs, the impurity binding energies in 1s-like state and 2p-like state have the same trend with the increase of QW width. However, the transition energies of impurity states between 1s-like state and 2p-like state in three shaped QWs are different. When the width of QW is fixed, the transition energy in square QW is the minimum and that in V-shaped QW is the maximum. The effect of electric field is larger for the on-center donor impurity. The effect of electric field on the impurity states is the largest in square QW and the smallest in V-shaped QW.

First Principle Investigation of Structural, Electronic and Optical Properties of Quaternary BxInyGa1−x−yN Compounds

We report on our results obtained on the physical properties of BxInyGa[Formula: see text]N quaternary alloys in the zinc-blende phase that are thoroughly considered by the linearized augmented plane wave method, with a full potential within density functional theory, for different concentrations [Formula: see text] and [Formula: see text] as employed in the Wien2k code. We calculated the structural properties, including lattice constant [Formula: see text] and the bulk modulus [Formula: see text]. We computed as well the band structures, the dielectric constant and the refractive index of our quaternary alloys compounds. Finally, nonlinear dependence on the compositions [Formula: see text] and [Formula: see text] are investigated in-depth and still expecting for experimental confirmations. To the best of our knowledge, this is the first theoretical investigation of BxInyGa[Formula: see text]N alloy conducted to date.

The Effect of Sn Doping on the Thermoelectric Properties of SiGe Using First Principle Technique

The thermoelectric properties of hexagonal SiGe doped with Sn with doping percentage of 12.5% and 25% were investigated using linearised augmented plane wave method using the WIEN2k package and semiclassical Boltztmann Transport equation using the BoltzTraP software for the purpose of understanding the role of Sn as a dopant in the SiGe. For temperature range of 300 to 1000 K, it can be seen that by doping with Sn, there is an improvement in overall thermal conductivity of the samples with the highest improvement is in the 25% doped sample. The conductivity vs temperature for 25% Sn doped SiGe also shows higher value through temperature range from 300 K to 1000 K, however the Seebeck coefficient decreases with Sn doping percentage for the same temperature range. Due to lower Seebeck coefficient and higher thermal conductivity values, the overall thermoelectric coefficient, ZT, of the doped compound is lower than the SiGe values with highest ZT equal to 0.29 and 0.17 at 650 K for 12.5% and 25% respectively while the ZT of simulated SiGe at 650 K is 0.35. Thus 25% Sn doping actually reduce the ZT but enhanced the thermal and electrical conductivity of SiGe for temperature range of 300 to 1000 K.