PHOTOINDUCED SURFACE-REACTIONS OF REVERSE-BIASED N-TYPE POROUS SI

Light induced surface reactions of reverse-biased n-type porous Si wit h H2O, CH3OH or CF3COOH are studied by diffuse reflectance and transmi ssion Fourier transform infrared spectroscopy. The goal of this work i s to identify reagents which will react with the irradiated, electron deficient surface but not the non-irradiated, neutral surface of rever se-biased porous Si. The porous Si is the anode in an electrochemical cell with the desired reagent present as the electrolyte solution. H2O /0.5M NaCl is found to react with the reverse-biased Si in both the li ght and the dark to form the native oxide. CH3COOH/0.1M NABF(4) genera tes a small amount of methoxide-modified Si in both the light and the dark. CF3COOH/1M CF3COONa reacts with the surface when the porous Si i s optically excited to create a surface-bound trifluoroacetic ester sp ecies. CF3COOH/1M CF3COONa does not react with reverse biased Si in th e dark. The Si surface can be 3 photolithographically patterned with t he trifluoroacetic ester species. (C) 1996 American Vacuum Society.