Electrical studies on oxygen ionosorption at ambient pressure on SnO 2(In) thin films

Abstract

Temperature ranges in n-type semiconductor thin films such as SnO 2, where oxygen ionosorption at ambient pressure increases the resistivity and O − 2, O − and O 2− ions are present were directly determined by simple electrical measurements. Conductance measurements were made in a constant flow of inert atmospheres (N 2 or Ar), in synthetic air or in synthetic air containing reducing gases like H 2 and CO. In Arrhenius diagrams the slopes of ln G versus 1/ T vary from negative (normal for semiconductors) to positive when the temperature is raised. This happens if thin films are placed in both air and in inert environment. By studying activation energies for conductivity and isothermic oxygen adsorption-desorption, in two different environments we have established the following temperature intervals: (a) O − 2 ionosorption occurs (370–520 K), (b) O 2 desorbs (520–570 K), (c) O − (O 2−) is successively ionosorbed (570–620 K), (d) it desorbs ( T > 620 K). The results are discussed in terms of H 2 sensing mechanisms in SnO 2 thin films.