THE GROWTH AND CHARACTERIZATION OF SI1-YCY ALLOYS ON SI(001) SUBSTRATE

We have prepared Si1-yCy alloy layers on Si (001) substrates using solid-source molecular-beam epitaxy. The lattice mismatch between diamond and Si is about 50%. Thus, a Si1-yCy (y = 0.02) alloy has a mismatch of about 1% with respect to Si assuming Vegard's law. Transmission electron microscopy (TEM) shows the layers to be pseudomorphic. Growth temperatures between T(g) = 500-550-degrees-C are suitable for Si1-yCy layers with y less-than-or-equal-to 0.05 for a growth rate of about 0.2 nm/s. Raman spectra show a distinct phonon mode at 600 cm-1, which is characteristic of substitutional carbon in Si. The Raman spectra show no evidence of silicon carbide precipitates, nor are precipitates observed in the cross-sectional TEM micrographs. This is consistent with the lattice constant measurements by x-ray diffraction. Amorphous growth occurs for lower substrate temperatures or significantly higher carbon concentration. That means, with increasing y in the Si1-yCy alloy layer the substrate temperature must be increased moderately. We have also studied the thermal stability of Si1-yCy strained-layer superlattices and find that the layers are stable to about 800-degrees-C (for y = 0.015). The ability to grow high-quality Si1-yCy alloy layers and Si1-yCy/Si superlattices adds a new dimension to Si-based band-gap engineering with the possibility for integration of a potential wide band-gap semiconductor into Si technology.