Semiconductor, topological semimetal, indirect semimetal, and topological Dirac semimetal phases of Ge_(1−x)Sn_x alloys

摘要

Electronic structures of Ge_(1−x)Sn_x alloys (0 ≤ x ≤ 1) are theoretically studied by the nonlocal empirical pseudopotential method. For relaxed Ge_(1−x)Sn_x , a topological semimetal is found for x > 41% with gapless and band inversion at the Γ point, while there is an indirect-direct band-gap transition at x = 8.5%. For strained Ge_(1−x)Sn_x on a Ge substrate, semimetals with a negative indirect band gap appear for x > 43%, and the strained Ge_(1−x)Sn_x on Ge is always an indirect band-gap semiconductor for x < 43%. With appropriate biaxial compressive strains, a topological Dirac semimetal is found with band inversion at Γ and one pair of Dirac cones along the [001] direction.