Adsorption Effect Transistor Influence of Humidity on the Response of Water

Abstract

The semiconducting thin films whose thickness is smaller than the Debye length act as a unipolar transistor controlled by the positions and densities of surface states, because of the gate action of space-charge-potential barriers with polarized characteristics. When certain atmospheric constituents are chemisorbed on such semiconducting films to form the surface states, the film conductivity appreciably varies. Such films can be utilized as highly sensitive gas sensors which are named adsorption effect transistors (AET).The resistance of a stannic oxide film AET at 400°C under humid air was investigated experimentally. The drain resistance decreases with increasing humidity. It is thought that water chemisorption donors are responsible for the phenomenon. However, this situation reverses in the higher humidity range, which is enhanced with increasing humidity and the drain voltage, respectively.In order to explain this anomalous increment in the resistance, a possible mechanism was introduced: The water adsorption produces ionic conduction channel on semiconductor surface Faint current through this channel causes a electrode reaction at the surface of the semiconducting film covering a platinum electrode. This reaction produces surface acceptors and results in the detectable increment in the film resistance because of the AET characteristics. © 1980, The Chemical Society of Japan. All rights reserved.