Effects of ageing on porous silicon photoluminescence: Correlation with FTIR and UV-Vis spectra

An analysis about the change of photoluminescence (PL) intensity during ageing in porous silicon (p-Si) at room temperature (RT) is reported. PL measurements have been correlated to Fourier transform infrared spectrometry (FTIR), UV-Vis reflectance spectra (RS) and transmission electron microscopy (TEM) with the aim of clarifying the basic mechanism of the luminescence intensity variation. After six months of ageing we observed a value of the PL intensity approximately 200 times greater than at beginning together with a blue-shift of 50 nm. The FTIR experiments evidenced that an oxygen passivation effect associated to the quantum confinement model allows to justify the observed behaviour under ageing; moreover the absorption edge of about 2 eV determined by the reflectance measurements corresponds to the high energy tail of the PL spectra. TEM images are also in agreement with the shift of the gap and with the wire shrinkage due to the SiO2 layer observed by IR spectra. Copyright (C) 1996 Elsevier Science Ltd.