Electrochemical Phenomena in Thin Films of Silicon Dioxide on Silicon

A study has been made of the effect of chemical additives and of annealing and electrical biasing procedures upon the state of charge of silica films grown on silicon. A model, proposed to account for the observations, is based on the assumption that phosphorus, aluminum, and boron, when present, substitute for Si in SiO2. The resulting species may be represented as PO2+, PO2−, AlO2−, or BO2−. The mobile charge carrier in the silica under the conditions investigated here is assumed to be an oxide-ion vacancy. Under certain conditions electrolysis is accompanied by deviations from Faraday's laws and changes the net charge in the oxide; under other conditions only the charge distribution in the oxide is changed. The experiments leading to the development of the model, which were done with metal-oxide-silicon structures, have been supplemented with experiments with field effect transistors. Field effect transistors of the n-p-n type have been made to operate in the enhancement mode.