Nanosecond QFRS study of photoluminescence in amorphous semiconductors

The paper is concerned with the study of the photoluminescence (PL) lifetime distribution of a-Si : H and a-Ge : H, down to the nanosecond (ns) region using a newly developed dual-phase, double lock-in (DPDL) quadrature frequency-resolved spectroscopy (QFRS). The DPDL-QFRS results show no indication of a peak in the ns region, and the PL lifetime distribution is basically double-peaked with slow (approximate to ms) and fast (approximate to mus) components, as reported earlier. The double-peak lifetime, a blue-shift of the fast component spectrum against the slow one, a dependence of the radiative transition rate on the PL emission energy and a fast lifetime (similar to mus, this being much longer than singlet-exciton lifetime normally (similar to ns)) can be well explained by invoking self-trapped excitons. A singlet-triplet exchange energy similar to 40 meV is deduced for a-Si : H. The dependence of the lifetime distribution on the generation rate is discussed on the basis of the non-geminate recombination, where nongeminate pairs prevail over excitons under strong photoexcitation conditions. (C) 2003 Kluwer Academic Publishers.