Existence of direct bandgap transitions in Si/SiO₂ superlattices

We present tight-binding bandstructure calculations for {Si}_m{SiO₂}_n crystalline superlattices (SLs) grown along the [001] direction. The results show that strong quantum confinement occurs in the short-period SLs. A particularly interesting feature of the results is the almost nested bandstructure along the ZΓ line of the SL-Brillouin zone. This feature is even more attractive than having just a direct bandgap in obtaining high radiative efficiencies. These results suggest the possibility of novel optical devices which exploit the nested bandstructure, and have implications for our understanding of the luminescence in porous-Si and other Si-based nanostructures.