ELECTRONIC-BAND PARAMETERS IN STRAINED SI(1-X)GE(X) ALLOYS ON SI(1-Y)GE(Y) SUBSTRATES

A systematic theoretical study of the electronic properties of pseudomorphic (100)-strained Si1-xGex alloys grown on unstrained Si1-yGey 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 Si1-yGey substrate for 0.7 < y < 1 (type-I alignment), in contrast to any Si-rich combination of active layer and substrate.