In SituCharacterization of the Illuminated Silicon-Electrolyte Interface by Fourier-Transform Infrared Spectroscopy

The illuminated $n$-Si/aqueous-N${\mathrm{H}}_4$F 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 ${\mathrm{cm}}^{-1\mathrm{}}$ 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 ${\mathrm{Si}}^{2+}$ intermediate which can disproportionate to form a hydrogenated amorphous silicon overlayer which builds up progressively as photoetching proceeds.