Optical properties of structurally relaxed Si/SiO2 superlattices:: The role of bonding at interfaces -: art. no. 165339

We have constructed microscopic, structurally relaxed atomistic models of Si/SiO2 superlattices. The structural distortion and oxidation-state characteristics of the interface Si atoms are examined in detail. The role played by the interface Si suboxides in raising the band gap and producing dispersionless energy bands is established. The suboxide atoms are shown to generate an abrupt interface layer about 1.60 Angstrom thick. Band structure and optical-absorption calculations at the Fermi golden rule level are used to demonstrate that increasing confinement leads to (a) direct band gaps, (b) a blue shift in the spectrum, and (c) an enhancement of the absorption intensity in the threshold-energy region. Some aspects of this behavior appear not only in the symmetry direction associated with the superlattice axis, but also in the orthogonal plane directions. We conclude that, in contrast to Si/Ge, Si/SiO2 superlattices show clear optical enhancement and a shift of the optical spectrum into the region useful for many opto-electronic applications.