Photoluminescence enhancement and degradation in porous silicon: Evidence for nonconventional photoinduced defects

We report results concerning photoluminescence (PL) enhancement and degradation in fresh and oxidised porous silicon (PS). The PL evolution is explained by being based on three dissociated phenomena such as hydrogen photodesorption, photooxidation and nonconventional photocreated defects. It was found that time evolution of PL spectra depends on ambient atmosphere and PS porosity. An increase of the PL intensity followed by a degradation occurs after a short interruption of laser excitation, depending on temperature. This PL behaviour is attributed to relaxation of nonradiative recombination centres like photoinduced defects other than Si dangling bonds. It was pointed out that these photoinduced defects have a density and a relaxation time depending on laser power and temperature.