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 SiO
2
. The resulting species may be represented as PO
2
⁺
, PO
2
⁻
, AlO
2
⁻
, or BO
2
⁻
. 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.