Direct observation of oxygen-induced luminescent states in porous silicon by tunable excitation time-resolved spectroscopy

Time-resolved photoluminescence (TRPL) using a dye laser pumped by a N2 laser has been employed to clarify the recombination processes of carriers selectively excited to energy levels ranging from 3.68 to 1.94 eV in oxidized porous silicon (PS). Selective excitation of carriers to energy levels around 2.7±0.4 eV significantly enhances the radiative recombination probability. The decay time of this enhanced PL is estimated to be about 4 ns. This PL enhancement is considered to be due to the creation of oxygen-induced defect states which are located at the oxidized surface layer and/or the interface between the Si bulk and the SiOx layer.