Meyer-Neldel Rule in Ac Conductivity of Cu Doped ZnO Thin Films

Ac charge transport mechanisms have been comparatively investigated in ZnO thin films having different Cu dopant. A comparative study of the applicability of quantum mechanical tunelling and correlated barrier hopping model to obtained ac electrical conductivity results has been performed. Comparing the temperature dependence of the frequency exponent shows that the correlated barrier hopping model best describes the experimental data on the ac conductivity in ZnO:Cu thin films. In order to gain an understanding of the applicability of Meyer-Neldel rule, the dependence of the thermal activation energy on Cu doping concentration in these films has also been studied. The obtained experimental results indicated that Meyer-Neldel rule can be succesfully applied ac conductivity data for highly Cu doped films but not others which has been explained on the basis of distribution variations in density of states.