Frequency-dependent conductivity in As2Se3 and As2Te3 thin films

D.c. and a.c. conductivity measurements have been performed on amorphous As2Se3 and As2Te3 thin films. As2Se3 and As2Te3 samples were subjected to fields of the order of 100-103V/cm and their d.c. conductivities were measured at temperatures between 197 and 423K. The conductivity shows an exponential relation with the temperature of type D*s=D*s0exp(-E/kT). An application of the results to the above relation indicates a dominance of extended state conduction. The a.c. conductivities of As2Se3 and As2Te3 samples were measured at temperatures between 228 and 373K in the frequency range between 5Hz and 1MHz. The results suggest that the conductivity consists of two components, one being independent of frequency and the other varying as D*wswith frequency. The data are found to fit the correlated barrier hopping (CBH) model, especially at low temperatures. The a.c. data show a good agreement with the quasi-universal law predicted by the extended pair approximation (EPA). Quantitatively, the agreement is less good. The wavefunction decay length and the exponent derived from the data are not as satisfactory. These discrepancies cast doubt on the universality of the EPA. There may be more material dependency than expected.