Photoluminescence decay and hydrogen desorption of n-type porous silicon

The decay under illumination of the photoluminescence (PL) intensity of n-t ype porous silicon (PS) samples prepared by electrochemical etching has bee n investigated. We have found that the PL evolution with illumination time presents two different stages: an initial very fast decay which lasts simil ar to 300 s, followed by a second one, much slower, which extends for times longer than 10(4) s. This evolution suggests that two different mechanisms could be responsible for the PL intensity decay. Samples subjected to diff erent illumination times were studied by Thermal Desorption Spectroscopy (T DS). The desorption rate of H-2 and SiHx species was monitored during linea r heating of the samples. A qualitative correlation between the decay of th e PL intensity under illumination and the amount of H-2 and SiHx species ev olved from the illuminated samples has been observed. Experimental data sug gest that H-2 could be desorbed from the sample during the illumination tim e through a photoinduced H-2 desorption process, inducing the decrease of t he PL intensity.