Two-dimensional tight-binding model of ac conductivity in porous silicon

A time-dependent tight-binding model has been developed to study the ac conductivity in porous silicon. Assuming that carriers are allowed to hop between isolated pairs of Si nanocrystals embedded in a SiO2:, matrix, the tunneling times have been calculated according to different geometries. The geometrical structure of porous silicon has been modeled with simple percolationlike clusters. By using the tunneling times, the ac conductivity behavior in the high-frequency regime has been calculated in the pair approximation. The conductivity increases with the frequency according to a power law with an exponent lower than unity. It is found that there is a strong dependence of the ac conductivity on the thickness of the SiO2 interconnecting layer. (C) 1998 American Institute of Physics.