Quantum confinement and direct-bandgap character of Si/SiO₂ superlattices

We present tight-binding bandstructure calculations for {Si}_m{SiO₂}_n crystalline superlattices (SLs) grown along the [001] direction. A striking new feature of the results is the essentially direct band-gap structure along the ZΓ symmetry line of the SL-Brillouin zone which has a blue shifted energy gap due to quantum confinement. This feature is very attractive for obtaining high radiative efficiencies. These results suggest the possibility of novel optical devices which exploit the direct bandstructure, and have implications for our understanding of the luminescence in porous-Si and other Si-based nanostructures.