Band anticrossing in highly mismatched Sn_xGe_1−x semiconducting alloys

We show that at dilute Sn concentrations (x<10%), the composition dependence of the direct band gap and spin-orbit splitting energies of Sn_xGe_1−x can be described by a valence band anticrossing model. Hybridization of the extended and localized p-like states of the Ge host matrix and the Sn minority atoms, respectively, leads to a restructuring of the valence band into E₊ and E₋ subbands. The notably large reduction in the band gap follows from an upward shift in the valence band edge by approximately 22 meV per x=0.01. These results demonstrate that like III-V and II-VI compound semiconductors, group IV elements may form highly mismatched alloys in which the band anticrossing phenomenon is responsible for their unique properties.