Infrared studies of gas adsorption on semiconductor surfaces (1979)
AuthorsUde Shankar, S.show all
The interaction of various gases on evaporated germanium and silicon surfaces has been studied at room temperature (27°C) by means of infrared spectroscopy. Water vapour has been found to dissociate on germanium surfaces as a result of which bands have been observed at 1980-60, 770 and 675, and at 730 and 875-825cm-¹. These are attributed to three adsorbed species; the first to Ge-H, the second pair to Ge-OH groups and the third pair to Ge-O- and oxygen incorporated in the lattice respectively. From the observed changes in the Ge-H band intensity (in the presence of water vapour) a mechanism is proposed for H₂ formation over the surface, as a result of the reaction: The adsorption of ammonia on germanium gave rise to a number of bands which are attributed to three different surface species. These are physically adsorbed ammonia, co-ordinated ammonia, and a primary amine group. On oxidised germanium the interaction is found to be much weaker, although some dissociation is thought to occur since in addition to the bands corresponding to a primary amine a sharp hydroxyl band has also been observed. A different mode of adsorption to that proposed by Bennett and Tompkins is suggested for carbon dioxide adsorption on germanium. The interaction is thought to occur between the oxygen atoms of carbon dioxide and surface germanium atoms. Some evidence for dissociation of carbon dioxide is suggested by the appearance of a band near the gas-phase frequency of carbon monoxide. The interaction of oxygen on silicon surfaces has been found to give rise to a number of bands during different stages of exposure to oxygen. At very low exposures a peroxide-like silicon-oxygen surface structure is proposed by comparison with data obtained by other workers. At high exposures a bulk oxide species is thought to be responsible for two strong bands which show logarithmic growth.