A first-principles study of the vibrational and thermodynamic properties of GaBixAs1-x alloys

Studies on GaAsBi-based devices have been deeply carried out in recent years, strongly driven by their excellent performance. Despite the growing interest in GaAsBi, the systematic researches on its vibrational and thermodynamic properties are still lacking. Hence, in this work, the structural, vibrational and thermodynamic properties of GaBixAs1-x are studied systematically by performing ab initio calculations. Firstly, the calculation structure constants of GaBixAs1-x are in accordance with other available data in the literature. Next, the results of the vibrational frequencies indicate that the phonon frequencies of GaBixAs1-x undergo a sharp decline when the bismuth concentration x is elevated. Besides the reduction of the phonon densities of states at the specified wave vector, the optical branches of GaBixAs1-x narrow and the attenuation of longitudinal modes is greater than that of transverse modes with the enhancement of the Bi concentration x. Then, the splitting degree δω\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left( {\delta \omega } \right)$$\end{document} suggests that the ionic strength for GaBixAs1-x is declined when increasing the Bi composition. Finally, the thermodynamic functions of GaBixAs1-x ranging from ΔF\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta F$$\end{document},ΔE\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta E$$\end{document},Cv\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$C_{v}$$\end{document} and S\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$S$$\end{document} are predicted. In addition, the calculation values of the Debye temperature for GaBixAs1-x also confirm the change trend of phonon frequencies of the system.