Model for optical absorption in porous silicon

In this paper we analyze the optical absorption in porous silicon. This is the first attempt to explicitly demonstrate that it is not possible to extract the band gap of low-dimensional nanostructures like porous silicon from a Tauc plot of root alpha (h) over bar omega vs (h) over bar omega. So we model the absorption process assuming that porous silicon is a pseudo-one-dimensional material system having a distribution of band gaps. We show that in order to explain the absorption we specifically need to invoke the following: (a) k is not conserved in optical transitions, (b) the oscillator strength of these transitions depends on the size of the nanostructure in which absorption takes place, and (c) the distribution of band gaps significantly influences the optical absorption. A natural explanation of the temperature dependence of absorption in porous silicon also follows from our model.