Fundamental band gap and direct-indirect crossover in Ge_(1-x-y)Si_xSn_y alloys

摘要

The Ge-like indirect band gap of Ge_(1-x-y)Si_xSn_y, alloys has been determined over an extended y ＞ x range using photoluminescence spectroscopy from films grown on Ge-buffered Si substrates. It is found that the compositional dependence of this transition can be fit with a bilinear expression of the form (in eV): E_(ind) = (0.668±0.008) + (0.67±0.15)x - (l.77±0.16)y. These energies are significantly below the prediction from a simple linear interpolation between Si, Ge, and α-Sn, revealing a large negative bowing in the compositional dependence similar to that found earlier for direct transitions. The direct-indirect crossover boundary is found to lie along the compositional line y = (0.062 ± 0.014) + (0.76 ± 0.23)x, which in the limit x → 0 agrees with earlier results for the binary Ge_(1-y)Sn_y alloy.