Electronic properties of vacancy-oxygen complexes in SiGe alloys

Capacitance transient techniques, combined with ab initio modeling, were employed to study the electronic properties and structure of vacancy-oxygen (VO) complexes in unstrained Czochralski-grown Si_1-xGe_x crystals (0<x≤0.06). At least three configurations of the VO center in SiGe alloys have been identified. The most stable configuration consists of a Si-O-Si unit and a Ge-Si reconstructed bond in a vacancy. This configuration is about 0.2 eV more stable than separated VO and Ge defects and possesses an acceptor level which is about 25 meV deeper compared to the level of the VO center without a Ge atom in a nearest-neighbor site. Two configurations with a Ge atom in the second nearest-neighbor shell around an off-center oxygen atom have been found to be stable. One of these configurations has an acceptor level, which is about 15 meV shallower than that for the VO complexes with more remote Ge atoms.