Physics of the indirect- to direct-gap transition in group-IV semiconductor alloys

Development of CMOS-compatible photonic devices as a Si photonics enabling technology has stimulated efforts to engineer direct-gap group-IV semiconductors. Demonstrated lasing in Ge_1-xSn_x alloys has driven strong interest, and prompted investigations of Ge_1-xC_x and Ge_1-xPb_x alloys.

Despite strong experimental activity detailed analysis of Ge_1-x(C,Sn,Pb)_x has been limited, with distinct mechanisms proposed to describe the emergence of a direct band gap based on chemical trends observed in III-V semiconductors. Recent analysis has revealed the nature of the band structure of Ge_1-x(C,Sn,Pb)_x alloys, highlighting that alloy band mixing effects play a critical and overlooked role [1-3].

We combine first principles and empirical atomistic calculations to analyse the nature and evolution of the electronic structure of Ge_1-x(C,Sn,Pb)_x alloys, providing a unified understanding of the electronic properties of this emerging class of semiconductors.

[1] C. A. Broderick et al, J. Appl. Phys. 126, 195702 (2019)
[2] E. J. O'Halloran et al, Opt. Quant. Electron. 51, 314 (2019)
[3] C. A. Broderick et al, arXiv:1911.05679 (2019)