Observation of Meyer–Neldel rule in CdS thin films

A study of electrical transport in CdS thin films is reported. We have observed, for the first time, that CdS thin film conductivity obeys the Meyer–Neldel rule (MNR). This was deduced from linking the conductivity pre-exponential factor to the activation energy variation. CdS films were deposited by chemical bath deposition at different solution temperatures in order to vary the electrical activation energy of the films. A correlation between the MNR rule and the disorder in the film network is highlighted. The multi-trapping process in the band tail-localized states governs the conductivity in CdS films. This explains the MNR observation in CdS films. The variation of the electrical conductivity pre-exponential factor and activation energy are correlated to the disorder in the film network; this was explained in terms of polaron formation and phonon–electron coupling with disorder.