ELECTRONIC-STRUCTURE OF [111]SI/GE SUPERLATTICES

Using ab initio pseudopotentials the authors have performed self-consistent calculations on Sin/Gen strained layer superlattices grown on a (111) silicon substrate for n=1, 2, 3 and n=6. They look at the electronic structure and find that, despite strain and folding effects, none of these superlattices have a direct gap. From charge density contours a complete localization of the upper valence band states at the Gamma point is found on the germanium sublattice for the n=6 case. Such localization does not occur for superlattices grown on (001) substrates with the same repeat distance.