Quest for an optoelectronic material: tetragonal Si xGe 1− x films

Abstract

We report experiments in which we attempted to grow Ge and Si 0.2Ge 0.8 films with a tetragonal crystal structure on InP(001). The substrate was chosen because it has approximately the same lattice constant as the tetragonal Si xGe 1− x a-axis lattice constant. The tetragonal structure has been observed previously in Ge, and has a 1.5-eV bandgap. Theory predicts that the gap is direct, which implies that tetragonal Si xGe 1− x films are suitable for optoelectronic devices. Growth on the InP(001) (2×3) and (2×4) reconstructed surfaces was investigated. Some evidence for the tetragonal phase was obtained for the growth of Si 0.2Ge 0.8 at 100 °C on the two reconstructions, but no evidence was obtained for growth of either tetragonal Si 0.2Ge 0.8 or Ge on the (2×3) reconstruction for growth temperatures at or above 130 °C. We conclude that tetragonal Si x Ge 1− x films on InP(001) does not seem to be a technologically feasible material system.