Boron segregation in single-crystal Si_1-x-yGe_xC _y and Si_1-yC_y alloys

It has been reported that boron segregates to single-crystal Si _1-xGe_x layers from silicon during thermal anneals. In this work, we find that boron segregates even more strongly into single-crystal Si_1-x-yGe_xC_y, as has been previously reported for polycrystalline films. This effect is also observed in single-crystal Si_1-yC_y. Segregation coefficients range from 1.7 to 2.9 for annealing temperatures in the 800-850°C range. In a Si _1-yC_y layer with 0.4% carbon, most of the segregation is reversible if the carbon is removed by an oxidation-enhanced out-diffusion process. This argues against the formation of immobile B-C defects as the driving force for the segregation. Gradients of interstitial silicon atoms, created by high concentrations of substitutional carbon, are presented as a driving force capable of causing the segregation seen in the experiments.