Existence of direct bandgap transitions in Si/SiO2 superlattices

We present tight-binding bandstructure calculations for {Si}(m){SiO2}(n) cr ystalline superlattices (SLs) grown along the [001] direction. The results show that strong quantum confinement occurs in the short-period SLs. A part icularly interesting feature of the results is the almost nested bandstruct ure along the Z Gamma line of the SL-Brillouin zone. This feature is even m ore attractive than having just a direct bandgap in obtaining high radiativ e efficiencies. These results suggest the possibility of novel optical devi ces which exploit the nested bandstructure, and have implications for our u nderstanding of the luminescence in porous-Si and other Si-based nanostruct ures. (C) 1999 Elsevier Science B.V.