Model for carrier dynamics and photoluminescence quenching in wet and dry porous silicon thin films

A simple model of electron kinetics, previously used in molecular and protein electron dynamics, is applied to transport and photoluminescence in wet and dry porous Si. Porous Si is modeled as a system of touching Si nanocrystals that individually show strong three-dimensional confinement. In the presence of a polar liquid in the pore structure, the electron-polar molecule dynamical coupling is an order of magnitude stronger than the electron-Si acoustical-phonon coupling. Dry porous Si shows resonant tunneling kinetics, while wet porous Si shows fast, activationless, highly exothermic transfer typically characteristic of protein systems. The calculations explain why photoluminescence is strong in dry porous Si, while conductivity and electroluminescence are enhanced in wet porous Si. It is suggested that hot carrier relaxation rates in Si nanostructures would be faster in a polar environment. © 1996 The American Physical Society.