The growth and characterization of Si1−yCy alloys on Si(001) substrate

Abstract

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 Tg=500–550 °C are suitable for Si1−yCy layers with y≤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 °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.