Electronic Band Parameters Research Articles

Electronic structure calculations for ZnS xSe 1− x

Energy band gaps and electron effective mass as well as their composition dependence are the most critical parameters for band structure calculations of semiconductor alloys. Therefore, an accurate knowledge of these parameters is very important. Unfortunately, there is a limited experimental and theoretical information in the literature regarding the electronic band parameters for zinc blende ZnS x Se 1− x . This has incited us to carry out such calculations. For this purpose, we have used the empirical pseudo potential method within the Virtual Crystal Approximation and the effect of compositional disorder is treated as an effective potential. The band gap variation versus sulfur concentration x shows two different behaviors: clear diminution of gap energy for low concentrations, and quasi-linear behavior with a small bowing for large values of x. Furthermore, the calculated effective mass shows that the disorder is not only compositional but also structural.

Effects of hydrostatic pressure and temperature on electronic band parameters in AlxGa1?xAs

Influence of hydrostatic pressure and temperature on electronic band parameters for zinc-blende AlxGa1−xAs was investigated by means of pseudopotential calculations. The agreement between our results and the available experimental data is generally satisfactory. Our results showed that the effect of pressure leads to a decrease of the crossing point and the optical bowing parameter. However, the temperature effect was found to be insignificant on both crossing point and bowing parameter.

Predicted electronic properties of zinc-blende Zn 1− xMg xSe alloys

Based on the pseudopotential scheme, the electronic properties of zinc-blende Zn 1− x Mg x Se alloys have been predicted. The agreement between our calculated electronic band parameters and the available experimental data is generally reasonable. These parameters are found to depend non-linearly on alloy composition x. The electron valence and conduction charge densities derived from pseudopotential calculations for certain concentrations are also reported.

Electronic band parameters for zinc-blende Al1−xGaxN

Band-structure calculations are performed for cubic Al1−xGaxN usingthe empirical pseudopotential method. The band gaps at Γ,X and L points and the electron effective masses of Γand X valleys are calculated as a function of the gallium fractionx.It is found that there is no significant change in these electronic bandparameters on taking into account the alloy disorder. On the basis of amodel solid theory, we have calculated the band discontinuities forheterointerfaces between strained Al1 −xGaxN and relaxed Al1−yGayN.The latter calculations are extended to the whole range of compositionsx andy. Theinformation derived from this investigation will be useful in the design oflattice-mismatched heterostructures in blue-light optoelectronics applications.

Electronic Properties of the Alloy System GaxIn1-xPySbzAs1-y-z Lattice Matched to InAs

We have investigated the electronic properties of the pentanary alloy GaxIn1–xPySbzAs1–y–z/InAs by means of the pseudopotential method under the virtual crystal approximation. To the best of our knowledge, such a scheme has been used for the first time for studying pentanary alloys. The composition dependence of electronic band parameters for the alloy of interest has been calculated. Our results are compared to literature data obtained by other theoretical methods.

Electronic structure of PbTe near the band gap

Existing experimental data for the electronic band parameters of the conduction and valence bands of PbTe are analyzed and compared using a multiband model electron dispersion relation. The model permits the identification of inconsistencies among the data and the derivation of an improved set of band parameters. Among the principal conclusions are (i) the most commonly used value of the transverse-conduction-bandedge effective mass is too large; (ii) the conduction- and valence-band mass anisotropy ratios vary only weakly with carrier concentration, in contradiction to much of the early data for $p\ensuremath{-}\mathrm{PbTe}$; (iii) existing theoretical calculations of the far-band contributions to the conduction- and valence-band-edge effective masses are not in very good agreement with experiment.

Electronic energy band parameters of graphite and their dependence on pressure, temperature and acceptor concentration

Electronic energy band parameters of graphite and their dependence on pressure, temperature and acceptor concentration

Electronic energy band parameters of graphite and their dependence on pressure, temperature and acceptor concentration

An analysis has been made of experimental data on the dependence of electronic properties of graphite on pressure and acceptor concentration, using the Slonczewski-Weiss dispersion relationship for the free carriers. It is shown that such experiments cannot be interpreted adequately without taking into account all of the band-overlap parameters in this theory. Previous workers had particularly neglected the influence of the parameter γ 3, which trigonally warps the constant energy surfaces. The results presented will also be useful for interpreting new experiments in which either the band overlap parameters or the Fermi-energy are changed. A discussion of possible changes in band parameters with temperature is included.

Radiation effects on the spectral response of HgCdTe

We present a theoretical model for the effects of electron irradiation on the bulk electronic energy band parameters of HgCdTe. The material is treated as degenerate. We predict irradiation induced changes in the shape of spectral response and resolve apparent inconsistencies in the HgCdTe photoresponse data. Qualitative, overall changes in photoconductive detector response are predicted and we find a general trend that short wavelength materials are less susceptible to the effects of radiation.

Evaluation of energy band parameters of carbons

The systematic dependence of the Hall effect of carbons on the electronic band parameters has analytically been studied on the basis of Yazawa's band model which takes into account in a simple way the interlayer perturbation. Many experimental results on the magnetic-field dependence of the Hall effect of carbons can be satisfactorily explained by adjusting the band parameters. The change in the Hall voltage with the band parameters is so drastic as to provide a powerful tool for evaluating these parameters of carbons. The evaluation procedures are described in detail and some examples of the application to experimental results presented. It is concluded that as-deposited pyrolytic graphite has a high concentration of acceptors with small activation energy (~ l0 meV), which may probably originate from the structural defects. On the other hand, the activation energy of boron in graphite is found to exceed 100 meV.

Electrical Transport Properties of Graphite Assuming Lattice Scattering

The theory for acoustical phonon scattering in graphite is combined with the appropriate electron band model and the transport theory based on the relaxation-time approximation to calculate electrical conductivity and thermoelectric power along the $\mathrm{ab}$ planes. Contributions from both majority and minority carriers are included. Basal-plane electrical conductivity and thermoelectric power data from 50 to 600 \ifmmode^\circ\else\textdegree\fi{}K for well-oriented graphite materials are analyzed. Assuming presently accepted values for electron band parameters, including a negative value for ${\ensuremath{\gamma}}_{2}$, data for the thermoelectric power cannot be explained as long as the material is considered to be an ideal graphite. Data above 300 \ifmmode^\circ\else\textdegree\fi{}K can be fit very well if an acceptor density of 2.2\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ is assumed with an energy level of 0.01 eV below the majority bands at ${k}_{z}=\ifmmode\pm\else\textpm\fi{}\frac{\ensuremath{\pi}}{{c}_{0}}$. Calculated results below room temperature with this acceptor density agree qualitatively with experiment. It is therefore concluded that either well-ordered graphite materials have \ensuremath{\approx} 1 impurity (or defect) for every ${10}^{4}$ carbon atoms which acts as an acceptor, or refinement of the analytical approach is required, including the possibility of considering different values for band parameters.

Cyclotron wave propagation in silver

Azbel'-Kaner cyclotron resonance in metals is accompanied by electromagnetic waves propagating in a direction perpendicular to the magnetic field. Taking into account the anisotropy of the silver Fermi surface, the dispersion relation for these waves is calculated in the limit where the wavelength is much smaller than the orbit diameter of the electrons. Thus it is shown that a number of previously observed oscillations in the surface impedance of a semiinfinite silver specimen arise from points of zero-group velocity on the dispersion relation. Physically, the oscillations reflect a matching of the electron-orbit diameter with an integer number of wavelengths. They may, therefore, be looked upon as geometric resonances in the surface impedance, complementary to the temporal cyclotron resonances. The surface impedance is calculated under the assumption of specular surface scattering. Satisfactory agreement with experiments is obtained by using an independent-particle model for the electron gas and band parameters based on APW calculations. The influence of the Fermi-surface geometry is demonstrated by comparing with calculations for a cylindrical and a spherical Fermi surface. The electric field in the metal is calculated for selected magnetic fields, and the expected result of a transmission experiment is presented. Finally, the absence of Fermi liquid effects in the experiments is briefly discussed.