Recombination of geminate pairs in As₂Se₃ single crystals

Abstract

Simultaneous measurements of photoconductivity and photoluminescence reveal the steps of geminate-pair recombination in As₂Se₃ crystals where only geminate pairs are found to contribute to the emission of light. High electric fields increase the photoconductivity and reduce the luminescence by changing the balance between geminate and non-geminate pairs. The dependence on temperature of this balance yields a detailed description of geminate-pair recombination, which is predominant for excitation energies near the absorption threshold. Free excitons with binding energy of 47 meV are created, which then rapidly relax into a deeper state most likely by self-trapping. Resonant luminescence is not observed. The lifetime of the relaxed state is limited at low temperature (< 50 K) by radiative decay. At higher temperatures non-radiative channels with activation energies of 40 and 150 meV reduce the luminescence efficiency.