Luminescence Study of Thermally-Oxidized Porous Si under Subgap or Overgap Excitation

Abstract

The temperature dependence and the temporal decay of photoluminescence from thermally-oxidized porous silicon have been studied under 1.80 or 2.54 eV excitation which is below or above the optical bandgap value of 2.2 eV determined from the luminescence excitation spectrum. No significant difference between luminescence spectra under the subgap and the overgap excitation is observed at emission energies below 1.65 eV. The luminescence under the subgap excitation exhibits a weak temperature dependence compared to the overgap excitation case. This can be interpreted in terms of the suppressed thermal emission-rate for carriers photogenerated near the radiative recombination centers to the extended states. It is also revealed that, in the pulsed subgap excitation, the luminescence shows a fast decay in the time region below 1 µs and a slow decay component follows, as observed in the case of the pulsed overgap excitation. The carriers photogenerated directly at radiative recombination centers or neighboring sites under the subgap excitation are likely to be responsible for the observed fast decay.