Band alignments of coherently strained Ge(x)Si(1-x)/Si heterostructures on <001>-Ge(y)Si(1-y) substrates.

The self-consistent "ab initio" pseudopotential results of Van De Walle and Martin have been combined with the phenomenological deformation potential theory of Kleiner and Roth to estimate the bandgap and band-offsets for coherently strained multilayers of Ge(x)Si(1-x)/Si for growth on <001>-Ge(y)Si(1-y) substrates. 

It is found that DeltaE(o) is negligible and TYPE 1 band alignments result if the Si in the multilayers is cubic (unstrained), whereas DeltaE(o) can be appreciable and TYPE II band alignments may result if both the Si and the Ge(x)Si(1-x) are strained. In particular, the present results explain the recent modulation doping results of Jorke et al. (for two dimensional electrons) and People et al. (for two-dimensional holes).