Synthesis of Porous Silicon by non-contact etching with a strong oxidizer*

Porous silicon thin films have been produced by photochemical synthesis with a solution of hydrofluoric acid (HF) and the oxidizer cobalt nitrate. A 20mW HeNe laser was used to produce the local electric field necessary for the formation of the porous matrix on the surface of the crystalline silicon (n-type, antimony doped) substrate. Samples prepared with variations in process time from 15 minutes to 5 hours were examined using photoluminescence and Raman spectroscopy as well as scanning electron microscopy. Results indicate that the presence of the oxidizer during synthesis enhances the intensity of the photoluminescence produced by the porous silicon post-processing when compared with samples prepared using only HF. In addition, post process analysis reveals that the porous layer on the samples is present only on samples processed for less than 2 hours.