Electronic-band parameters in strained ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ alloys on ${\mathrm{Si}}_{1\mathrm{-}\mathit{y}}$${\mathrm{Ge}}_{\mathit{y}}$ substrates

A systematic theoretical study of the electronic properties of pseudomorphic (100)-strained ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ge}}_{\mathit{x}}$ alloys grown on unstrained ${\mathrm{Si}}_{1\mathrm{-}\mathit{y}}$ ${\mathrm{Ge}}_{\mathit{y}}$ substrates is presented. Based on nonlocal empirical pseudopotential calculations with spin-orbit interactions, realistic estimates of the conduction- and valence-band-edge energies, higher-energy-band minima, effective masses, deformation potentials, and heterostructure band offsets for the whole range of alloy compositions x and y and strain are presented. The theory predicts that the band edges of weakly stressed Ge fall within the wider gap of the ${\mathrm{Si}}_{1\mathrm{-}\mathit{y}}$ ${\mathrm{Ge}}_{\mathit{y}}$ substrate for 0.7<y<1 (type-I alignment), in contrast to any Si-rich combination of active layer and substrate.