In situ infrared evidence for the electrochemical incorporation of hydrogen into Si and Ge

The electrochemical incorporation of hydrogen into n-Si and n-Ge has been studied by Fourier-transform electrochemically modulated infrared spectroscopy. Fresh (111) silicon (resp., germanium) surfaces exhibit a vibrational band at 2080 (resp., 1960) cm^-1 corresponding to a surface Si - H (resp., Ge - H) bond perpendicular to the surface. Prolonged cathodic treatment results in a new band at 2000 (resp., 1900) cm^-1. The position and polarization dependence of this band indicate that it is associated with hydrogen inside the semiconductor lattice. These observations directly show for the first time that cathodically hydrogenated samples contain a thin, disordered, and highly hydrogenated layer, which is probably responsible for the improvement of the hydrogen evolution kinetics observed on these electrodes.