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 pseudom orphic (100)-strained Si1-xGex alloys grown on unstrained Si1-yGey sub strates is presented. Based on nonlocal empirical pseudopotential calc ulations with spin-orbit interactions, realistic estimates of the cond uction- and valence-band-edge energies, higher-energy-band minima, eff ective masses, deformation potentials, and heterostructure band offset s for the whole range of alloy compositions x and y and strain are pre sented. 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 (t ype-I alignment), in contrast to any Si-rich combination of active lay er and substrate.