UV photooxidation induced structural and photoluminescence behaviors in vapor-etching based porous silicon

In this paper, we investigate the effect of UV irradiation on Vapor-Etching (VE) based Porous Silicon (PS) structure and luminescence under controlled atmosphere (N2, air, O2). The oxidation evolution is monitored by Fourier transform infrared (FTIR) spectroscopy. FTIR measurements show that the SiHx bond, initially present in the freshly prepared PS layers, decreased progressively with UV irradiation time until they completely disappear. We found that this treatment accelerates the oxidation process. SiOx structures appear and gradually become dominant as regard to the SiHx species, while UV irradiation is in progress. Generally, the photoluminescence (PL) intensity of the PS layer decreases instantaneously at the starting by the UV excitation and stabilizes after a period depending on the ambient gas and the specific surface area of the porous structure. Further UV exposure leads to a linear decrease of the PL intensity due to change of surface passivation from SiHx to OySiHx. After less than 100 min of UV irradiation, the PL intensity exhibits an exponential decay. UV exposure in air and O2 leads approximately to the same PL behavior, although faster PL intensity decrease was observed under O2-rich ambient. This was explained as being due to intense hydrogen desorption in presence of oxygen. Correlations of PL results with FTIR measurements show that surface passivation determine the electronic states of silicon nano-crystallites and influence the photoluminescence efficiency.