On the energy dependence of the absorption constant and photoconductivity near a direct band gap

Abstract

The absorption of light by a crystal in a spectral region in which direct excitons are observed can best be described as the creation of some (generally complicated) final state by an optical transition through an intermediate exciton state. The energy of the intermediate states determine the absorption line positions, but it is the final states which determine the line shape and are of interest in photoconductivity. A formalism is developed which expresses the absorption line shape in terms of an energy-dependent line width, whose form depends on the final states. This point of view is used to discuss some exciton line shape and photoconductivity experiments in CdS and Cu₂O.