Microwave plasma oxidation (below 200 °C) of partially strain-compensatedSi1−x−yGexCy(Ge:C=20:1 and 40:1) with and without a Si cap layer is reported. The electrical properties of grown oxides have been characterized using a metal–oxide–semiconductor structure. Fixed oxide charge density and mid-gap interface trap density are found to be2.9×1011/cm2and8.8×1011/cm2/eV,respectively, for directly oxidizedSi0.79Ge0.2C0.01film. The oxide on samples with low C (0.5&percent;) concentration, exhibits hole trapping, whereas electron trapping is observed for oxides on alloys containing 1&percent; C. ©1998 American Institute of Physics.