The role of ambient ageing on porous silicon photoluminescence: evidence of phonon contribution

From the study of the isotherm adsorption of gas at lowers temperatures (BET), we have determined the pore size distribution in porous silicon (PS) and the specific surface area (SSA). We show that these results are in good agreement with those calculated by PL modelling. The structure of aged PS has been studied through the effect of excitation energy on the photoluminescence (PL) spectrum. The PL band is broadened and shifted to lower energy compared to the calculated gap distribution. This shift is approximately the energy of one TO phonon. At low temperature, several peaks and fine structures are observed on the PL band for different excitation energy. They could be attributed to phonons assisted PL process from dot crystallites having discrete distribution of sizes. Resonant PL shows a strong coupling SiOSi vibration mode-exciton that contributes to the increase of the broadening of the PL band by the apparition of additional bands in the PL spectra.