Theoretical description of gas-film interaction on SnO

The Hall measurements recently reported by Chang and Hicks (S. C. Chang and D. B. Hicks, in D. Schuetle and R. Hammerle (eds.), Fundamentals and Applications of Chemical Sensors, American Chemical Society, Washington, DC 1986, p. 58) are a useful test of the influence of reducing gases on free carrier and mobility variations. It is demonstrated here that a simple depletion model for the gas-solid interface adequately accounts for the free carrier and mobility response of the SnOx films. Expressions for the relationship between the surface potential, bulk carrier concentration and the reducing gas concentration are derived using the standard semiconductor electrostatic surface model and first-order kinetic equations for gas-solid interactions. The role of film structure and the interaction of surface and bulk Schottky defects is discussed.