Practical strategies for tuning optical, structural and thermal properties in group IV ternary semiconductors

Recently synthesized SiGeSn ternary alloys offer the possibility of varying their composition and thus their optical behavior while maintaining the lattice parameter at a constant value. In this paper we use theoretical calculations to show that the bandgap of Ge_1-X (Si_0.8Sn _0.2)_X derivatives can be varied from 0.8 to 1.1 eV (X = 0-0.5) at a fixed lattice constant identical to Ge. We also show that Sn clustering in the diamond cubic structure can alter both the magnitude and character (direct/indirect) of the bandgap in these systems, particularly at high Sn concentrations. First principles thermochemistry simulations were finally used to calculate the Gibbs free energy and demonstrate that the mixing entropy is responsible for the stabilization of the ternary alloys with respect to GeSn binaries of the same Sn content consistent with experimental observations.