ELECTRICAL-CONDUCTIVITY OF AIR-EXPOSED AND UNEXPOSED LEAD-TELLURIDE THIN-FILMS - TEMPERATURE AND SIZE EFFECTS

Thin films of PbTe of different thicknesses have been prepared on glass substrates at room temperature by vacuum deposition. The electrical resistivity of the air-exposed films is much higher (by about 2 to 3 orders of magnitude) than that of the as-grown (unexposed) thin films. The electrical resistivity temperature behaviors of both types of film are different but both show hysteresis behavior during successive heating-cooling cycles. These observations are explained by considering that the desorption of absorbed gas molecules (mainly oxygen) and creation of defects at higher temperatures during heating influence the electrical conduction. Further, the time factor involved in gas desorption-adsorption can cause the observed hysteresis in temperature-dependent conduction behavior. The as-grown (unexposed) thin-film conductivity exhibits the expected reciprocal thickness dependence due to the thickness effect, but the air-exposed film conductivity does not. This is attributed to the complete masking of the thickness effect by the gas adsorption effect in air-exposed film conductivity.