A Model for the Optical Absorption in Pororus Silicon

TL;DR

This paper models the optical absorption in porous silicon as a pseudo 1D system with a distribution of band gaps, highlighting the roles of non-conserved momentum, nanostructure size, and band gap distribution.

Contribution

It introduces a model accounting for non-conservation of momentum and size-dependent oscillator strength to explain porous silicon's optical absorption.

Findings

Absorption depends on nanostructure size and band gap distribution.

Standard methods cannot accurately determine the band gap from absorption data.

Non-conservation of momentum is essential to explain the absorption process.

Abstract

In this paper, we report on the optical absorption in porous silicon. We model the absorption process assuming that porous silicon is a pseudo 1D material system having a distribution of band gaps. We show that in order to explain the absorption we specifically need to invoke - (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. We also show that it is not possible to extract the band gap of porous silicon from a plot of $\sqrt{\alpha\hbar\omega}$ vs $\hbar\omega$.