THEORY OF OPTICAL-PROPERTIES OF POLYSILANES - COMPARISON WITH POROUS SILICON

We have studied the electronic structure of sigma-bonded silicon chain s containing between 2 and 66 silicon atoms. Stable atomic configurati ons are obtained by minimization of the total energy. The exciton spec trum is calculated by diagonalization of the full matrix of the Coulom b interaction taking into account the electron-hole exchange interacti on. We predict important atomic relaxations that give polaronic effect s for free molecules and explain the observed Stokes shifts. We show t hat the luminescence properties of silicon chains strongly depend on t he interactions between the molecules and the medium in which they are embedded. The energy, the size, and the radiative lifetime of exciton s are computed and their dependence on the size of the molecules is an alyzed. We deduce that chains of silicon atoms are probably not at the origin of the visible luminescence of porous silicon but could explai n its fast band in the blue region.