Tuning the Electronic Structure of Si1-xGex Alloys

Abstract

Abstract: Binary alloys of Si_1−xGe_x, where x is the Ge composition, have attracted much attention as functional materials of both micro-electronic and opto-electronic devices in recent years. In this study, we employ first-principles density functional theory (DFT) and k.p method to study ground states of the Si_xGe_1-x (x = 0-1) alloys. In the systems, most physical properties of the indirect semiconductors are retained which are principally described by the ground states. An interesting property of Si_1−xGe_x alloys that is their electronic band structures are tunable between those of bulk Si and Ge. The conduction band minimum of Si shifts gently from a point along ΓX path to the L point with the increased Ge composition x. The band structures of Si_1-xGe_x alloys calculated by the k.p method are consistent with the results from DFT calculations. We also find that band topology changes along ΓL path yield various quantum transitions which may give rise to the changes of external quantum efficiency. The theoretical results provide comprehensive understanding for recent experimental observations on the shift of the absorption energy assigned to E1 direct transitions within L and Γ points in the Brillouin zone of Si_1-xGe_x alloy nanocrystals.

Keywords: Si-Ge alloy nanocrystals, electronic structure, and ground state, density
functional theory.