First-principles Study on the Electronic Structures and the Optical Properties of Hg(1-x)Cd(x)Te
The electronic structures and the optical properties of the direct-band-gap infrared alloy Hg(1-x)Cd(x)Te (x = 0.250, 0.375, 0.500, 0.625, 0.875, and 1.000) were obtained using the local spin density approximation (LSDA) in the density functional theory (PET). The calculated lattice constants are in agreement with these calculated using Vergard's law and the band structures of these alloys are similar. The three peaks of the imaginary part in the dielectric function reveal that the conduction bands lift with increasing a. The calculated static dielectric constants of these alloys were shown to behave as a parabolic function. The results for the loss functions and effective electronic densities show that few electrons take part in the interband transitions.
Available from: Bang-Gui Liu
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ABSTRACT: We use a modified Becke—Johnson exchange plus a local density approximation correlation potential within the density functional theory to investigate the electronic structures of Hg1−xCdxTe and In1−xGaxAs with x being 0, 0.25, 0.5, 0.75, and 1. For both of the two series, our calculated energy gaps and dielectric functions (real part ∊1 and imaginary part ∊2) are in agreement with the corresponding experimental results with x being between 0 and 1. The calculated zero-frequency refractive index varies greatly with x for Hg1−xCdxTe, but changes little with x for In1−xGaxAs, which is consistent with the real parts of their dielectric functions. Therefore, this new approach is satisfactory to describe the electronic structures and the optical properties of the semiconductors.
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ABSTRACT: The structural, electronic and optical properties of mercury cadmium telluride (Hg1−x Cdx Te; x = 0.0, 0.25, 0.5, 0.75) alloys are studied using density functional theory within full-potential linearized augmented plane wave method. We used the local density approximation (LDA), generalized gradient approximation (GGA), hybrid potentials, the modified Becke–Johnson (LDA/GGA)-mjb and Hubbard-corrected functionals (GGA/LDA + U), for the exchange-correlation potential (E ex). We found that LDA functional predicts better lattice constants than GGA functional, whereas, both functionals fail to predict the correct electronic structure. However, the hybrid functionals were more successful. For the case of HgTe binary alloy, the GGA + U functional predicted a semi-metallic behaviour with an inverted band gap of −0.539 eV, which is closest to the experimental value (−0.30 eV). Ternary alloys, however, are found to be semiconductors with direct band gaps. For the x = 0.25 and 0.50, the best band gaps are found to be 0.39 and 0.81 eV using LDA-mbj functional, whereas, the GGA-mbj functional predicted the best band gap of 1.09 eV for Hg0.25Cd0.75Te alloy, which is in a very good agreement with the experimental value (1.061 eV). The optical properties of the alloys are obtained by calculating the dielectric function ɛ(ω). The peaks of the optical dielectric functions are consistent with the electronic gap energies of the alloys.
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