EXPERIMENTAL-STUDY OF OXYGEN EFFECT ON THE VARIATION OF RESISTIVITY WITH TEMPERATURE FOR POLYCRYSTALLINE SELENIUM THIN-FILMS

A correlation between the temperature dependence of the resistivity of polycrystalline selenium thin films and the presence of oxygen at the grain boundaries is established. The temperature dependence of the dc and ac resistivity and the thermoelectric power of thin film structures are studied as functions of thermal history and ambient gas exposure (argon, air atmosphere, dry oxygen, helium). Annealing at 413 K for 4 h under oxygen results in a decrease of the room temperature resistivity and an increase of the resistivity with increasing temperature from 290 to 350 K. Evidence that these effects are due to oxygen diffusion at the grain boundaries is deduced from ac conductivity dependence of planar structures, thermoelectric measurements, and ESCA studies.