THEORETICAL-STUDY ON THE ELECTRONIC-STRUCTURE OF (SI)M/(GE)N SUPERLATTICES

The electronic structures of (Si)m/(Ge)n superlattices with (001) stacking were studied by using the linear-muffin-tin-orbital method. A simple scheme of a self-interaction correction was implemented in order to predict the semiconductor band gap quantitatively. As the ten-layer periodicity is particularly suitable for realizing direct-band-gap superlattices, we studied several modulated superlattices (Si)m'/(Ge)n'/(Si)m''/(Ge)n'' . . . with m'+n'+m''+n''+ . . . = 10. We found interesting variations in the symmetry of the conduction-band bottom state and also in the wave-function confinement in the Si layer with regard to the variation in the set of (m',n',m'',n'',. . .). These results were analyzed with simple models. The dipole transition probability was also estimated. Some calculations were also performed to discuss the alloying effects at the interface for the (Si)4/(Ge)4 superlattice on the Si substrate.