Carrier dynamics in oxidized porous silicon

Abstract

A systematic study of carrier dynamics in oxidized porous silicon (PS) has been carried out using both steady-state and time-resolved photoluminescence (TRPL) measurements probed by tunable excitation over the photon energy range 3.68–1.94 eV for a temperature range 20 K to room temperature. The TRPL results show two emission bands, a high energy band (HEB) and a low energy band (LEB) with distinctively different temperature dependence that is attributed to different and competing carrier recombination mechanisms. The origin of the HEB PL is identified as oxygen-induced defect states with a broad distribution of 2.5±0.3 eV. These oxygen-induced defect states act as radiative recombination centers into which selective excitation of carriers results in the pronounced enhancement of the PL with the decay time of 5–6 ns. The LEB with the decay time of microsecond order is located around 2.1–2.0 eV. The time decay behavior and thermal quenching of the LEB PL intensity at less than 100 K are very similar to that of amorphous materials characterized by carrier recombination via band-tail states. Taking into account the results of the tunable-excitation steady-state PL and TRPL, a plausible model is proposed to explain carrier recombination in oxidized PS based on an analogy with amorphous materials.