Conductivity and photoconductivity peculiarities observed in C₆₀ layers

Abstract

Thin layers of various thickness prepared from C60 with traces of C70 were studied. They were deposited by thermal evaporation on quartz, glass, p-Si or n-Si substrates. An apparatus fixing current values every 3 ms was used to measure and register the kinetics of layer conductivity and photoconductivity. Series of peculiarities were observed in the kinetics of the current when an electrical field was applied to illuminated or darkened samples. For example, when voltage is applied to the sample the current immediately rises to a certain value and then falls to a different quasi-stationary value. These peculiarities depend on the particular state of the samples. After analyzing the phenomena, a scheme explaining these peculiarities was proposed which relates mainly to intrinsic polarization. The influence, which these processes might exert on the photoconductivity and data accuracy, was discussed. A substantial influence of ambient humidity was determined. Our study of the observed changes showed that humidity did not substantially affect the generation-recombination processes in the bulk material, but predominantly the carrier transport mechanism.