Enhanced band-to-band tunneling in direct-gap group-IV Ge_1-xSn_x alloys: impact of alloy band mixing

The indirect band gap of Ge limits applications in several classes of devices. Band structure engineering via alloying with Sn has demonstrated direct-gap behaviour, allowing to develop Si-compatible post-CMOS devices such as tunneling field-effect transistors (TFETs) [1].

Recent analysis has shown that the indirect- to direct-gap transition in Ge_1-xSn_x is driven by alloy band mixing, with the hybridised nature of the alloy band gap having significant consequences for technologically-relevant material properties [2].

We analyse the impact of alloy band mixing and short-range disorder on band-to-band tunneling (BTBT) in bulk and nanowire Ge_1-xSn_x, using large-scale atomistic electronic structure and non-equilibrium Green's function calculations [3]. We demonstrate that band mixing drives rapid onset and increase of direct BTBT in Ge_1-xSn_x, and provide a quantitative evaluation of the potential of Ge_1-xSn_x as a candidate TFET platform.

[1] J. Doherty et al, Chem. Mater. 32, 4383 (2020)
[2] E. J. O'Halloran et al, Opt. Quant. Electron. 51, 314 (2019)
[3] M. Luisier and G. Klimeck, Phys. Rev. B 80, 155430 (2009)