Optical and electronic properties of SiGeC alloys grown on Si substrates

Abstract Metastable Si 1 − x − y Ge x C y alloys were grown by molecular beam epitaxy on (100) Si substrates. Solid elemental sources were used for the Si and Ge beams, and a resistively heated graphite filament was used for the C beam. Up to 3 at% of C was incorporated in the alloy layers. Optical transmission measurements showed that the absorption edge of thick layers increased to higher energies with increasing C fraction, and revealed the presence of SiC and GeC vibrational modes in the infrared. At low temperatures, the alloys showed significant photoluminescence. The bandgap energies of thick layers increased linearly with the C fraction and followed a linear dependence of the bandgap on composition. Measurements of the valence band density of states using X-ray photoelectron spectroscopy indicated that the valence band energy maximum increased with the C fraction relative to that of SiGe alloys of similar composition. Our results indicated that SiGeC alloys are promising materials for Si-based heterostructure devices.