Electronic structure and PL spectrum of the diffusion-limited model for porous silicon

We present the results of theoretical calculations for electronic structure s and photoluminescence (PL) spectrum of porous silicon whose morphology is generated through the diffusion limited aggregation process of pores in a two-dimensional honeycomb lattice. We have found that due to irregularity o f the structure most of its eigenstates near band gap are localized while s ome of them are relatively delocalized. The localization of the eigenstates near band gap causes band-gap narrowing analogous to the quantum confineme nt effect. Solving the time-dependent equations for the occupation numbers of the eigenstates, we show that the present model reproduces the stretched exponential decay of PL intensity observed in the experiments.