First-principles study on the AlAsXSb1-X alloys

Tan, Natalie Wee Sian (2022) First-principles study on the AlAsXSb1-X alloys. Final Year Project, UTAR.

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Abstract

The work conducted in this project aims to study the composition dependence of the energy gap values, Eg of the ternary alloy composites. The ground-state electronic properties of the AlAsxSb1-x semiconductor alloy composites were investigated using first-principles calculations of Density Functional Theory (DFT) within the Generalized Gradient Approximation (GGA) functional framework with the implementation of Perdew–Burke–Ernzerhof (PBE) exchange-correlation (XC). Projector Augmented Wave (PAW) pseudopotential was used in performing scalar relativistic calculations with the inclusion of non-linear core corrections of Engel–Vosko (EV93) exchange functional in the optimization of energy potentials and total energy. The energy band gap values of AlAs, AlSb and AlAsxSb1-x alloys were calculated and discussed, with obtained results mostly in agreement with values reported in theoretical and experimental figures. Band gap energy values obtained in this project for AlAs and AlSb were 1.48 eV and 1.22 eV, respectively. Standard deviation for the x values in AlAsxSb1-x of 0.25, 0.56 and 0.75 were 0.127 ± 0.003 eV, 0.404 ± 0.003 eV and 0.10 ± 0.001 eV, respectively, while the linear regression slopes for calculated band gap curve and the scissor corrected curve were 0.63 and 0.464, respectively. Deviation of the band gap curve relative to Vegard's linear curve was 0.125 ± 0.005 eV. In conclusion, these results are in accordance with experimental data as well as values reported in literature. It has been shown that there is a non-linear behaviour in the composition dependence, x of the band gap values for the ternary alloys, indicating the digression from Vegard's law, with evident downward bowing of the fundamental energy gap values obtained relative to the alloy fraction composition. There is clear indication of the indirect band gaps via the CBM along the L- and X-paths of the band structures as well as the distinct energy gap dependence on the arsenic composition, x. Recommendations on further study include additional crystal visualizations of supercell structures matching that of AlAs0.56Sb0.44 that also possess similar BZ structures similar to that of the constituent binaries, identification of the critical x value where crossover from indirect to direct band gap occurs and further attempts to perform calculations that procure results for AlAsxSb1-x random alloy structures.

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