Thermal stability and substitutional carbon incorporation far above solid-solubility in Si_1-xC_x and Si_1-x-yGe_xC_y layers grown by chemical vapor deposition using disilane

Growth conditions for epitaxy of S_1-x-yGe_xC_x and Si_1-xC_x alloy layers on (100) silicon substrates by rapid thermal chemical vapor deposition (RTCVD) with disilane as the silicon source gas are described and the Si_1-xC_x conditions are compared to previously reported RTCVD growth conditions for epitaxy of Si_1-xC_x using silane as the source gas. The thermal stability of the layers at 850°C in nitrogen is examined using x-ray diffraction as a measure of the average substitutional carbon concentration in the layers after annealing. A characteristic time constant to describe the reduction of average substitutional carbon concentration in the layer is extracted from the XRD measurements. The characteristic time constants are found to agree within a factor of 3 with that observed in previous reports. However, the time constants are found to depend more strongly on the as-grown substitutional carbon concentration than what is predicted by simple precipitation kinetics, assuming carbon diffusion to a constant number of nucleation centers.