The success of heterojunction quantum wells and quantum dots in III-Vs has not been extended to silicon because the ideal barrier, SiO 2 , is amorphous, preventing the formation of quantum structures with silicon. The possibility of a few monolayers of oxide inserted between adjacent silicon layers was proposed and realized with a superlattice (SL) structure consisting of Si-Si-O-Si-Si-Si, having a monolayer of oxygen in each period introduced by adsorption onto the 2 Â 1 reconstructed surface along the Si(1 0 0). Reduction of the period leads to a slight up-shift of the energy of the emitted light, indicating that the essential objective of boosting the optical transition by promoting direct transitions has not been realized. Annealing in H 2 +O 2 results in significant improvement in PL and EL, showing that specific defects, e.g., Si-O complexes may be responsible for the observed light emission. The role of Si-O complex being the origin of emission is further supported by the observation that the emission of visible light from polycrystalline Si and SiO 2 structure is similar to the epitaxial superlattice with oxygen. The computed strain in a new type of superlattices consisting of SiO 2 , and GeO 2 is much lower than the Si-O SL. The EL in Si-O superlattice with the use of a Schottky barrier to provide electron-hole accumulation allows double injection into states higher in energy than the bandgap of Si, a prerequisite for injection laser without the need to use a wide-band pn-junction.