Lifetime studies on crystalline silicon thin-films by photoluminescence measurements

A novel measurement and analysis method of determining individual excess carrier lifetimes in multilayer systems is presented. This is particularly interesting for the characterisation of crystalline silicon thin-film samples consisting of an electrically active epitaxial layer on top of a crystalline substrate. The analysis principle is based on a comparison between a measured photoluminescence intensity ratio and associated simulated radiative recombination ratios. It benefits from the fact that for low excess carrier lifetimes within the epitaxial layer the carrier concentration in the said layer is limited by bulk recombination, while for high carrier lifetimes surface recombination is dominating. Depending on which excess carrier lifetime is realised, the excess carrier level in the epitaxial layer is either strongly dependent or nearly independent from the epitaxial layer thickness. In order to verify this measurement and analysis principle, results of a set of crystalline thin-film samples with varying epitaxial layer thickness on a highly doped Czochralski substrate are presented.