Calculations on two forms of siloxenic clusters and periodic films have been performed to address the unusual luminescence in porous silicon and to further investigate how the optical gap varies as a function of hydroxyl- or hydrogen-passivator concentration. Within conventional approximations to the density functional theory, our optimized cluster calculations confirm that low-dimensional siloxenic complexes, of stoichiometry [Si]:[O]:[H] = 2:1:2, are most stable when the oxygen atoms form bridging bonds with pairs of silicon atoms. To aid in experimental characterization of siloxenic films, we present equilibrium geometries, electronic structures, chemically induced core-level shifts, and joint densities of states for two forms of siloxenic clusters.

• Received 17 May 1993

DOI:https://doi.org/10.1103/PhysRevB.48.17400