The electronic properties and structure of vacancy-oxygen (VO) complexes in Czochralski-grown ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ crystals $\mathrm{}(0<x<\mathrm{}0.06\mathrm{})\mathrm{}$ have been studied by means of capacitance transient techniques and ab initio modeling. At least three configurations of the VO centers 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 ${\mathrm{Ge}}_s$ 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. Several 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. The increase of the ionization enthalpy of the VO complexes with the increase in Ge content in ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ crystals is associated with changes in the average Si-Si bond length.

• Received 20 October 2003

DOI:https://doi.org/10.1103/PhysRevB.69.125218