NM04–Atomistic analysis of band-to-band tunnelling in direct-gap GeSn group-IV alloys

The emergence of a direct band gap in Ge1-xSnx alloys has stimulated interest in developing Ge_1-xSn_x alloys and nanostructures for applications in Si-compatible electronic and photonic devices. The direct band gap of Ge1-xSnx, combined with the strong band gap reduction associated with Sn incorporation, makes Ge1-xSnx a promising material system for the development of Si-compatible tunnel field-effect transistors (TFETs) due to an expected strong increase in band-to-band tunnelling (BTBT). Based on a semi-empirical tight-binding model, we establish quantum kinetic BTBT current calculations for atomistic Ge_1-xSn_x alloy supercells. Recent analysis suggests that Ge1-xSnx possesses hybridised conduction band edge states for x ≾ 10%. We demonstrate that Sn-induced band mixing opens up a pathway for direct BTBT in ordered alloy supercells, strongly enhancing BTBT current compared to Ge. The framework we establish allows for quantitative prediction of the properties and performance of Ge1-xSnx-based TFETs.