Atomistic analysis of localisation and band mixing effects in Gel-ϰC,Sn)ϰ group-IV alloys

摘要

We present a theoretical analysis of the electronic structure of the group-IV alloys Ge_1-x(C,Sn)_x. Our analysis is based on a semi-empirical tight-binding model, parametrised via hybrid density functional theory calculations. Using atomistic alloy supercell calculations we identify and quantify the respective roles played by C-related localised impurity states and Sn-induced band mixing in determining the nature of the indirect- to direct-gap transition in Ge_1-xC_x and Ge_1-xSn_x. For exemplar calculations on 64-atom Ge₆₃(C,Sn) (x=1.56%) supercells we derive and parametrise model Hamiltonians which provide quantitative and physically transparent descriptions of these localisation and band mixing mechanisms, and comment on the implications of the Ge_1-x(C₂Sn)_x alloy band structure for technologically relevant material properties.