In situ study of porous silicon thin films thermal oxidation by pulsed laser photoacoustics

Passivation is of remarkable importance for porous silicon (PSi) applications to guarantee the chemical stability of its high surface area through time. Thermal oxidation is one of the most common methods to passivate the surface of PSi. In order to better understand the oxidation process, here we performed an in situ study by using pulsed laser photoacoustics. During the thermal oxidation, the photoacoustical signal was measured each 1 °C from 70 °C to 900 °C. The measurements were analyzed by standard correlation, and the significant signal changes were related to the presence of different surface species. We have found temperatures, where the photoacoustical signal changes drastically, that can be related to the absorption and desorption of chemical species in the surface. Species identification where made through Fourier-transform infrared spectroscopy-attenuated total reflection analysis of the PSi samples, at temperatures around where these notorious modifications on the surface were observed. (paper)