Band alignments of coherently strained GexSi1−x/Si heterostructures on 〈001〉 GeySi1−y substrates

Abstract

The self‐consistent ab initio pseudopotential results of C. G. Van de Walle and R. M. Martin [J. Vac. Sci. Technol. B 3, 1256 (1985)] have been combined with a phenomenological deformation potential theory to estimate the band gap and band offsets for coherently strained multilayers of Ge_xSi_1−x/Si for growth on 〈001〉 Ge_ySi_1−y substrates. It is found that ΔE_c is negligible and the narrower Ge_xSi_1−x gap falls within the wider Si gap (type I band alignment) if the Si in the multilayers is cubic, whereas ΔE_c can be appreciable and the Ge_xSi_1−x conduction‐band edge tends to be higher in energy than the Si conduction‐band edge(type II band alignment) if both the Si and the Ge_xSi_1−x are strained. In particular, the present results resolve the seeming paradox which arose from interpretations of modulation doping experiments using heterojunctions grown either on Si〈001〉 substrates or on an unstrained alloy buffer layer.