Analysis of photoluminescence decay of excitons in CuInS_2 crystals

摘要

The time-resolved photoluminescence of free and bound excitons in bulk single-crystal CuInS_2 grown by the traveling heater method is examined. It is found that radiative decay of the free exciton at 1.535 eV and the bound exciton at 1.530 eV is exponential with two characteristic decay-times while that of the bound excitons at 1.525 and 1.520 eV is well-represented by a single exponent at low temperatures. The radiative lifetimes of the free exciton and the bound excitons at 1.530, 1.525, and 1.520 eV are obtained to be 320 ps, 500 ps, 2.1 ns, and 3.5 ns, respectively. A thermal release process of the observed bound excitons is discussed in terms of the obtained activation energy. The capture center cross-section for free exciton is also estimated. According to our estimates, a neutral charge is to be assigned to the defect centers associated with the observed bound excitons.