Electrical conductivity of air-exposed and unexposed lead selenide thin films: Temperature and size effects.

Abstract

Thin films of PbSe of different thicknesses have been prepared on glass substrates at room temperature by vacuum deposition. It is found that the electrical resistivity of the air-exposed films is much higher (by about 2 to 3 orders) than that of the as-grown (unexposed) thin films. The electrical resistivity temperature behaviors of both the air-exposed and as-grown (unexposed) thin films of PbSe are different. These observations can be explained by considering that the desorption of adsorbed gas molecules (mainly oxygen) and creation of defects at higher temperatures during heating influence the electrical conduction. The as-grown (unexposed) thin-film conductivity exhibits the expected reciprocal thickness dependence due to thickness effects, but the air-exposed film conductivity does not. This can be explained as due to the complete masking of the thickness effect by the gas-adsorption effect in air-exposed film conductivity. The reciprocal thickness dependence observed in the case of unexposed-film conductivity has been explained by the ``effective mean free path'' model. The mean free path ${l}_{g}$ and the specularity parameter p are determined as 580 A\r{} and 0.9, respectively.