In situ Characterization of the Illuminated Silicon/Electrolyte Interface by Fourier Transform Infrared Spectroscopy

摘要

The application of electrochemically modulated infrared spectroscopy has been particulary rewarding in the case of the metal/electrolyte interface, but there have been surprisingly few attempts to extend the method to the semiconductor/electrolyte interface. We have taken an approach which exploits the fact that in the case of a semiconductor the surface density of minority carries can be perturbed at constant potential by illumination. In this way it should be possible to modulate the rate of the surface reactions involved in photoetching and hence to detect the vibrational spectra of intermediate species. The illuminated n-Silicon/aqueous Ammonium Fluoride interface has been studied by attenuated reflectance infrared spectroscopy under conditions in which photoetching occurs. An anomalously strong Si-H stretch band was observed to develop in the region of 2100/cm when the silicon was illuminated. The intensity of the band was found to increase linearly with time under steady illumination, rapidly exceeding values corresponding to monolayer hydrogen coverage. The absorbance decayed slowly in the dark. The results indicate that the etching process involves a Si(II) intermediate which can disproportionate to form a hydrogenated amorphous silicon overlayer which builds up progressively as photoetching proceeds. Keywords: N type semiconductors. (AW)