Microstructural Characterization of Heteroepitaxial SiGeC Alloys

Heteroepitaxial growth of Group IV elements on Si is attracting increased attention because of the possibility of strain compensation in addition to bandgap engineering. The incorporation of the smaller C atom into Si_1-xGe_x binary alloys to compensate for the larger size of the Ge atom offers the prospect of lattice matching and hence strain-free growth. In our early work, ternary SiGeC alloy films with up to 2% C were epitaxial with excellent crystallinity and very few interfacial defects. However, with increased C content, the films developed considerable disorder away from the substrate and finally became amorphous. Moreover, even at low C contents (2-3%), it appears that substantial C is being incorporated interstitially rather than substitutionally into the covalent lattice.2 Our recent work has therefore been aimed at establishing growth conditions that enable the amount of substitutional C to be maximized while still maintaining high crystal quality.