Excitation-intensity dependence of shallow and deep-level photoluminescence transitions in semiconductors

Abstract

Photoluminescence characterization of semiconductors is a powerful tool for studying shallow and deep defects. Excitation-intensity-dependent measurements at low temperatures are typically analyzed to distinguish between exciton and defect related transitions. We have extended existing models based on rate equations to include the contribution of deep defects. Generally, it is observed that the photoluminescence intensity IPL follows a power law IPL∝ϕk with the excitation intensity ϕ. We show that the exponent k takes on values of multiples of 1/2. The values depend on the availability of additional recombination channels. Defect levels can saturate at high enough excitation intensities, leading to one or several crossover points from one power law behavior to another. Power law exponents different from n/2 can result from the transition region between two limiting cases of linear power laws. Model functions for the analytical description of these transitional excitation dependencies are derived and the analysis is applied to chalcopyrite thin films and to numerical data. The saturation effects of defects by excess carriers as well as the influence of deep recombination centers can be extracted with the help of the presented model, which extends existing theories.