Abstract
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 (≈ms) and fast (≈μs) 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 (∼μs, this being much longer than singlet-exciton lifetime normally (∼ns)) can be well explained by invoking self-trapped excitons. A singlet–triplet exchange energy ∼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 non-geminate pairs prevail over excitons under strong photoexcitation conditions.
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