Empirical Pseudopotential Method Research Articles

Bandgap tuning in ZnxCd1-xTe superlattices through variable atomic ordering.

We explore the entire search space of 32-layer ZnxCd1-xTe superlattices to find the structures that minimize and maximize the bandgap at each possible zinc concentration. The searching is accomplished through an accurate and efficient combination of valence force field dynamics, the empirical pseudopotential method, and the folded spectrum method. We also describe the use of an alternate preconditioner that improves the robustness and efficiency of the locally optimal preconditioned conjugate gradient's solutions to the folded spectrum method. The physical properties of these superlattices, such as their formation energies, bandgaps, densities of states, effective masses, and optical response functions, are investigated with density functional theory paired with hybrid functionals and compare well to available experimental measurements. It is revealed that the bandgap of ZnxCd1-xTe may change by up to 0.2eV depending on how the layers in the superlattice are ordered. Stacking order has a large, irregular effect on the effective masses, but optical response functions seem insensitive to it.

Analysis of tunneling probability in heavily doped 4H-SiC Schottky barrier diodes based on complex band structure considering barrier potential

The tunneling probability in heavily doped 4H-SiC Schottky barrier diodes (SBDs) is analyzed based on the empirical pseudopotential method (EPM). A method of calculating the tunneling probability within the WKB approximation using the EPM electronic states of bulk 4H-SiC has been reported. In the present study, to investigate the validity of this method, the tunneling probability is calculated by connecting the incident, transmitted, and reflected wavefunctions considering the barrier potential of a SBD instead of using the WKB approximation. Comparing the calculated results with and without the WKB approximation, the difference is found to be rather small. This suggests that we can safely use the WKB approximation with the bulk electronic states, which are obtained without considering the barrier potential, when calculating the tunneling current in the heavily doped 4H-SiC SBDs.

Wannier–Stark localization of electronic states in 4H-SiC MOS inversion layer

The electronic states in 4H-SiC MOS inversion layers are theoretically analyzed using the empirical pseudopotential method (EPM). The analysis shows that the Wannier–Stark localization occurs, which is absent in an effective mass approximation (EMA). The Wannier–Stark localization modifies the electronic states in the MOS inversion layers. A model is proposed to describe the in-plane dispersion of subbands affected by the Wannier–Stark localization. The differences between the EPM and EMA results for the subband energy levels and the in-plane effective masses are discussed.

A Theoretical Estimation of Optical, Vibrational and Structural Properties of II–VI Quaternary Alloy Zn0.5Cd0.5SySe1–y

We present a theoretical estimation of optical, vibrational, and structural properties of II–VI semiconducting quaternary alloy Zn0.5Cd0.5SySe1−y for 0 < y < 1 giving total 10 compositions. The estimation of refractive index, elastic constants, bulk modulus, and vibrational frequencies are performed using the important input parameters provided by the empirical pseudopotential method. In this method, the bandgaps are computed, and the alloying effects are modeled through the modified virtual crystal approximation. We have computed the static refractive index, static and high-frequency dielectric constants, longitudinal and transverse optical phonon frequencies, elastic constants, bulk modulus, and cohesive energy for 10 compositions of the alloy. The results are compared to other experimental and theoretical values wherever available.

Optical properties of ZnSe using linear response theory

The electronic structure and optical response of ZnSe are studied in this work. The studies are carried out using first-principles full-potential linearized augmented plane wave method. After settling the crystal structure, the electronic band structure of the ground state of ZnSe is calculated. Linear response theory is applied to study optical response considering bootstrap (BS) and the long range contribution (LRC) kernels for the first time. We also use the random phase and adiabatic local density approximations for comparison. A procedure based on empirical pseudopotential method is developed to find material dependent parameter α required in the LRC kernel. The results are assessed by calculating the real and imaginary parts of linear dielectric function, refractive index, reflectivity, and the absorption coefficient. Results are compared with other calculations and available experimental data. The results of LRC kernel finding α from the proposed scheme are encouraging and at par with the BS kernel.

Theoretical analysis of tunneling current in 4H-SiC Schottky barrier diodes under reverse-biased conditions based on the complex band structure

The tunneling current in heavily doped 4H-SiC Schottky barrier diodes under reverse-biased conditions is calculated based on the complex band structure by the empirical pseudopotential method. When the experimental values for effective mass and barrier height are assumed, the calculation result by the approximation assuming a parabolic complex band significantly underestimates the experimental tunneling current. In contrast, the calculation using the non-parabolic complex band by the empirical pseudopotential method we propose in this study reproduces the experimental result with better accuracy. These results imply that it is important to consider the non-parabolicity of the complex bands when calculating the tunneling current.

Pseudo-Potential Calculations of AlxIn1−xPySb1−y Alloys Under the Effect of Hydrostatic Pressure: Phonon Frequencies and Related Parameters

Based on the empirical pseudopotential method (EPM) modified with virtual crystal approximation (VCA), we report a detailed study of the pressure dependence of the phonon frequencies, sound velocity, and Debye temperature of AlxIn1−xPy Sb1−y alloys lattice-matched to GaSb, InAs, and InP substrates. There is a good agreement between our calculated results and the available data in the literature for the constituent’s binary compounds which gives support for those of the studied alloys. The phonon frequencies and sound velocity are increased nonlinearly by enhancing pressure and giving high results for the InP substrate than those of other substrates. The results in this work seem likely to be useful as a reference that we report for the first time.

Specific features of microhardness and thermodynamic stability of the Cd1–xMnxTe solid solutions

The features of fusion and growth of Cd1–xMnxTe (0.02 x  0.55) solid solution crystals as well as the dependence of their microhardness on the composition have been studied. Local maxima of the microhardness at x = 0.14 and 0.46 have been experimentally found. Thermodynamics of Cd1–xMnxTe formation in the delta-lattice parameter model has been considered, and the phase diagram of spinodal decomposition in these solid solutions has been found. The empirical pseudopotential method was used to analyze the distribution of the valence charge density during formation of the Cd1–xMnxTe solid solution and its effect on the rearrangement of chemical bonds. It has been shown that the stability of the solid solutions is defined not only by the difference in the lattice constants of the CdTe and MnTe binary compounds but also by the charge exchange between bonds with the different degree of ionicity and the change in the nature of chemical bonds.

On the Mechanical and Lattice Dynamic Properties of Nanostructure Pentanary GaxIn1−xPySbzAs1−y−z Alloy Lattice Matched to InP Substrate

The influence of composition on the energy band structure, mechanical properties, acoustic velocities, and optical phonon frequencies of the GaxIn1−xPySbzAs1−y−z alloy lattice matched to the InP substrate has been studied. To investigate the electronic structure and mechanical characteristics of the alloy under consideration, the empirical pseudo-potential method (EPM) was used. In this study, we consider the virtual crystal approximation (VCA). A good agreement between our results and the widely accessible published values was obtained. Our findings will serve as a crucial source for the next works. It has not been thoroughly investigated how composition affects the mechanical properties, optical phonon frequencies, and acoustic velocities of the researched alloys. Consequently, we were interested in these properties as they were affected by composition.

Structural and optical properties of GaAs and InAs for doping Sb under the effect of pressure and temperature: DFT and EPM investigations

We have developed first-principles calculations utilizing the empirical pseudopotential method and density functional theory to examine the basic behaviors of the GaAs and InAs semiconductor compounds for doped Sb. The electronic and optical responses of these compounds were calculated. We examined the impacts of the temperature and pressure with the energy band forbidden and parameters of optical parameters (static dielectric constant) of the considered compounds. The literature hasn’t fully analyzed the electronic and optical characteristics of the compounds with doping Sb under the impact of pressure and temperature for fixed composition (x = 0.5). So, we concentrated on the study of these properties.

Prediction of mechanical properties of In1-x GaxAsyP1-y lattice-matched to different substrates using artificial neural network (ANN)

ABSTRACT The mechanical properties, namely the elastic constants (C11, C12, and C44), bulk B, shear Cs, and Young’s modulus Y0, of the In1-xGaxAsyP1-y lattice-matched GaAs and InP substrates, were estimated using an artificial neural network (ANN method). This study aimed to create ANN networks that facilitate the estimation of the mechanical properties of alloys subjected to different temperatures and hydrostatic pressures. We aimed to predict the mechanical properties of InGaAsP alloys matched to InP and GaAs substrates as a function of temperature and hydrostatic pressure. ANN learning was performed based on the results validated by the empirical pseudopotential method data within the virtual crystal approximation, including the actual disorder potential. An ANN is a nonlinear process modeling technique frequently encountered in materials science. The predictive curves show high reliability, and underline the importance of using this approach to replace the time-consuming and costly experimental test, as well as to predict the mechanical response of the material where conventional modeling approaches have failed. Our method can consolidate the theoretical references found in the literature, it can also serve the field of engineering the mechanical properties of semiconductors, facilitate the successful design of optoelectronic devices, and serve future experimental works.

The Response of Phonon Frequencies, Sound Velocity, Electronic, Optical, and Mechanical Properties of Indium (Phosphide, Arsenide, and Antimonide) to Hydrostatic Pressure

The pressure dependence of phonon vibrations, the velocity of sound, and some other related physical quantities of and semiconductors have been determined. This investigation is done using the empirical pseudopotential method. We proposed a pressure dependence of the pseudopotential form factors; hence we were able to calculate the pressure dependence of the fundamental energy gaps. Using the values of the fundamental band gaps, we were able to calculate the refractive index, static dielectric constant, high-frequency dielectric constant, longitudinal and transverse phonon frequencies, elastic constants, mechanical moduli, and velocity of sound. Our findings may serve as a reference for experimental work at high pressures.

Electronic, optical, and mechanical properties of AlxIn1−xP alloys under temperature and pressure

In this work, the optoelectronic and mechanical properties of AlxIn1−xP combinations in the zinc-blende structure were studied for different Al concentrations. The energy band gaps left( {{text{E}}_{{text{g}}}^{{text{L}}} ,,{text{E}}_{{text{g}}}^{Gamma } ,,{text{E}}_{{text{g}}}^{{text{X}}} } right), refractive index (n), high frequency and static dielectric constants (ɛ∞, ɛo), elastic parameters (C11, C12, C44) were investigated. Other mechanical properties such as bulk (Bu), shear (Cs), Young’s (Y0) moduli, Poisson ratio (σ), linear compressibility (C_{o} ), Cauchy (C_{a} ) ratio, isotropy factor (A), bond stretching parameter (alpha ,), bond-bending force parameter (beta ,), internal-strain parameter (xi ), and the transverse effective charge (e_{T}^{*} ) were calculated. Also, the temperature and pressure dependences of these properties were studied. Our estimations were made with the empirical pseudo-potential method combined with the virtual crystal approximation incorporated the compositional disorder impact. There was a reasonable agreement between our determined outcomes and the accessible experimental values for the binary materials AlP and InP which give help for the consequences of the ternary combinations.

Simulation of the Band Structure of InAs/GaSb Type II Superlattices Utilizing Multiple Energy Band Theories

Antimonide type II superlattices is expected to overtake HgCdTe as the preferred materials for infrared detection due to their excellent photoelectric properties and flexible and adjustable band structures. Among these compounds, InAs/GaSb type II superlattices represent the most commonly studied materials. However, the sophisticated physics associated with the antimonide-based bandgap engineering concept started at the beginning of the 1990s gave a new impact and interest in the development of infrared detector structures within academic and national laboratories. InAs/GaSb superlattices are a type II disconnected band structure with electrons and holes confined in the InAs and GaSb layers, respectively. The electron miniband and hole miniband can be regulated separately by adjusting the thickness of InAs and GaSb layers, which facilitates the design of superlattice structures and optimizes the value of band offset. In recent years, both domestic and foreign researchers have made many attempts to quickly and accurately predict the bandgaps of superlattice materials before superlattice materials grow. These works constituted a theoretical basis for the effective utilization of the InAs/GaSb system in material optimization and designing new SL structures; they also provided an opportunity for the preparation and rapid development of InAs/GaSb T2SLs. In this paper, we systematically review several widely used methods for simulating superlattice band structures, including the k·p perturbation method, envelope function approximation, empirical pseudopotential method, empirical tight-binding method, and first-principles calculations. With the limitations of different theoretical methods proposed, the simulation methods have been modified and developed to obtain reliable InAs/GaSb SL energy band calculation results. The objective of this work is to provide a reference for designing InAs/GaSb type II superlattice band structures.

Impact of Substrates on the Electronic and Mechanical Properties of AlxIn1\u2212xPySb1\u2212y Alloys

The compositional dependence of electronic and mechanical properties of a AlxIn1−xPySb1−y quaternary alloy in zinc-blende structure lattice-matched to GaSb, InAs, and InP substrates is studied. The calculations are done based on the empirical pseudopotential method modified with virtual crystal approximation. Our calculations are obtained for the energy band gaps, elastic constants, elastic moduli, bond stretching, bond bending forces, and internal strain parameter. The material system of interest is found to be a direct semiconductor within a small range of Al concentrations about 0–0.07 and an indirect one outside this region. The Debye temperature and the Fröhlich coupling constant have been determined at different values of composition lattice-matched to different substrates. The phonon frequencies and the sound velocity for different substrates at various compositions have been studied. There is a good agreement between our results and the experimental data for its constituent binary compounds, AlP, AlSb, InP, InSb, and ternary alloys, InPSb, AlPSb, which supports the calculated results of the studied AlxIn1−xPySb1−y quaternary alloy. The studied properties for the considered alloy may be helpful for the fabrication of optoelectronic devices.

Thermal response of electronic, optical, mechanical properties, phonon frequencies, and sound velocity of InPxAsySb1\u2212x\u2212y/InAs quaternary semiconductor system

The temperature dependence of acoustic velocities, thermal properties, phonon frequencies, mechanical, electronic, and optical properties for the InPxAsySb1−x−y/InAs system has been studied. The physical properties of the binary components InSb, InP, and InAs that constitute the quaternary alloy were used in this research. The study has been done using the empirical pseudo-potential method (EPM) under the virtual crystal approximation (VCA). The thermal properties, phonon frequencies, and acoustic velocities for the InPxAsySb1−x−y/InAs system under the effect of temperature have not been fully studied. Therefore, we have focused on these properties under the influence of temperature. Due to the lack of published theoretical and experimental values on these properties, our findings will provide a significant reference for future experimental work.

Sound Velocity, Electronic, Optical, and Mechanical Properties for Nano Semiconductor Materials (CdTe, ZnTe) under the Influence of Pressure

The energy band structure, energy band gaps, refractive index, high-frequency dielectric constant, static dielectric constant, reflectivity, and susceptibility for CdTe and ZnTe have been determined. The elastic parameters, Young’s, bulk, shear moduli, Poisson ratio, anisotropic factor, and the internal strain parameter have been calculated for the CdTe and ZnTe. The acoustic velocity in the directions [001], [110], and [111] has been determined for the studied compounds. The pressure dependence of the investigated properties has been studied. The empirical pseudopotential method (EPM) was used to calculate our results. Our results at high values of pressure could be taken as a reference for future experimental and theoretical works. Generally, our results are found to be in good accord with experimental and theoretical data published in the literature. The data gained in this study could be useful in the development of optoelectronic devices under high values of pressure.

Elastic, lattice dynamical, thermal, electronic, and optical properties of nano-semiconductor CdTe under the effect of temperature

The energy band gaps of CdTe semiconductor material have been determined using the empirical pseudo-potential method (EPM). The refractive index (n), high frequency (ε∞) and static dielectric constants (εs) of the considered material have been studied. The elastic constants, as well as some associated factors like bulk, (Bu), shear (Cs), Young (Y0) moduli, isotropy factor (A), and Poisson ratio (σ), have been reported for CdTe in zinc blende structure. The longitudinal and transverse phonon frequencies (ωLO,ωTO), and Debye temperature (θD) have also been calculated. All of the variables studied have been investigated in terms of their temperature sensitivity. Generally, Our findings are in good agreement with those published in the literature. The studied material could be useful in the fabrication of optoelectronic devices under high temperatures.

Influence of pressure and temperature on mechanical and thermal behaviors of InAsSb and GaAsSb alloys

We have performed the first-principles calculations using the Density Functional Theory (DFT) and the empirical pseudopotential method (EPM) to study the fundamental behaviors of the InAsSb and GaAsSb semiconductors. The mechanical behaviors of InAsSb and GaAsSb alloys were calculated. Also, the thermal behaviors of InAsSb and GaAsSb alloys were investigated. We examined the impacts of pressure and temperature on the mechanical and thermal behaviors of the considered alloys. The mechanical and thermal behaviors of the InAsSb and GaAsSb alloys for composition (x = 0.5) under the influence of pressure and temperature haven’t been completely explored in the literature. Thus, we were interested in these behaviors under the pressure and temperature effects.

Electron and hole mobilities of GaN with bulk, quantum well, and HEMT structures

Electron and hole mobilities of GaN are calculated for three-dimensional (3D, bulk) and two-dimensional [2D, quantum well (QW), and HEMT] structures, including scattering processes of acoustic deformation potential, polar optical phonon, piezoelectric, ionized impurity, and so on. The calculated mobilities for 2D structures are strongly dependent on quantum well structures and impurity densities, although the temperature dependence of the mobilities behaves in a similar way to bulk values. In the present analysis, energy band structures of GaN are calculated by the empirical pseudopotential method including spin–orbit interaction, and then the electron effective mass of the conduction band and the hole effective masses of the valence bands are evaluated, which are used for the calculations of electron and hole mobilities. The calculated valence band structure of the heavy, light, and crystal field splitted valence bands reveal complicated dispersion due to the spin–orbit interaction. The obtained electron effective mass mc=0.145m is isotropic, and the heavy hole effective mass in the c∥ plane is mhh∥=1.20m, while in the c⊥ plane, the band edge effective mass is mhh0⊥=0.55m and the over all fitted heavy hole effective mass is mhh⊥=1.20m. The light hole effective masses are mlh∥=1.35m and mlh⊥=0.165m. Both of the electron and hole mobilities are limited by ionized impurity scattering at low temperatures and by polar optical phonon scattering at high temperatures. Calculated electron mobilities are 7100 cm2/Vs for bulk, 4600 cm2/Vs for high electron mobility transistor (HEMT), and 3600 cm2/Vs for QW at room temperature and calculated hole mobilities are 450 cm2/Vs for bulk, 450 cm2/Vs for HEMT, and 500 cm2/Vs for QW at room temperature. All the expressions for scattering rates and respective mobilities are derived for 3D and 2D (QW and HEMT) structures and enable readers to calculate electron and hole mobilities in different structures with parameters given in the table or modified ones.