PECULIARITIES OF SURFACE DOPING WITH CU IN SNO2 THIN-FILM GAS SENSORS

It is demonstrated that a small amount of Cu impurity (less than 1 at .%) significantly modifies the properties of tin oxide thin films used for the gas sensors. Different amount of C-ct (between 0.5 and 7 at . %) was sputtered on the top of the films. The structure, surface chemi cal composition, optical and electrical properties are studied for the se films. It is shown that the surface doping with the sputtered Cu le ads to nearly constant doping level in all the volume of the polycryst alline tin oxide thin film. It is shown experimentally that the select ivity of the resistance response to CO, H-2 and Cl-2 gases is improved for the tin oxide sensors by the small amount of the sputtered Cu. A correlation is revealed between the Cu effect and the electronic surfa ce states that were detected by the XPS and the optical analysis. (C) 1997 Elsevier Science S.A.