Theoretical study on the electronic structure of (Si)m/(Ge)nsuperlattices

The electronic structures of (Si${)}_{\mathrm{m}}$/(Ge${)}_{\mathrm{n}}$ 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${)}_{\mathrm{m}\prime }$/(Ge${)}_{\mathrm{n}\prime }$/(Si${)}_{\mathrm{m}\mathrm{″}}$/(Ge${)}_{\mathrm{n}\mathrm{″}}$ $\stackrel{\mathrm{̇}}{\mathrm{ct}}$ with m′+n′+m″+n″+$\stackrel{\mathrm{̇}}{\mathrm{ct}}$=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.