Measurement of Optical Constants of Wet Porous Silicon Using In Situ Photoconduction

Most techniques used to measure the optical constants of porous silicon (PSi) are based on dried samples, which may be contaminated by the environment, and require sensible setups as well as meticulous sample preparation, which could alter the PSi characteristics. Here, we show a method of determination of wet PSi optical constants using the analysis of the photocurrent-thickness curves acquired in situ in hydrofluoric acid during PSi formation. In particular, interference patterns in these curves allow the determination of the refractive index of the electrolyte-impregnated PSi. The photocurrent is proportional to the optical transmission through PSi. Processing only one sample in a single experiment was sufficient for the determination of the optical constants. The method shown here does not require any sophisticated sample preparation or handling, or high-precision optical instruments, while preserving fresh PSi layers, even for high porosities and for arbitrarily layer thicknesses. The method may be of interest in the fields of optical constant measurement, optical sensing using liquid media in PSi, or in situ optical monitoring of the evolution of wet PSi in various conditions. Here, PSi samples of different porosities were used with three different illuminations (633, 543, and 405 nm).