Oxygen-induced defect luminescence in porous silicon

Photoluminescence properties of oxidized porous silicon (PS) have been studied. Time-resolved photoluminescence (TRPL) measurements probed by tunable-excitation over the photon energy range 3.68−1.94 eV for temperatures of 20 K and room temperature show two emission bands, a high energy band (HEB) in the blue and a low energy band (LEB) in the red. 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 and is similar to photoluminescence observed in amorphous materials characterized by carrier recombination via band-tail states.