Effects of an External Electric Field from a Substrate on Conductance of SnO2 Thin Films

Abstract

Thin films of about 10 nm thickness were prepared by sputtering on substrates, and the effects of an external electric field from the substrate on the conductance of the film were investigated at 26°C and up to 300°C. The apparent conductance of the film increased with a positive substrate bias and decreased with a negative substrate bias. These field effects became more evident with larger bias and in films with a lower carrier concentration. By using metal oxide semiconductor theory, the results are attributed to the formation of a depletion and an accumulation layers in the film under a negative and a positive bias, respectively. The influence of electron traps in the film on its apparent conductance was suggested from calculations of these field effects. At temperatures above 150°C, slow changes in the conductance with time were observed under a constant negative bias. From the results measured in and in air, it was suggested that the amount or types of surface oxygen adsorbates changed under a negative electric field. These results indicate the possibility of controlling the electrical properties and the surface reactions of films by an external electric field.