Frequency Dependent Conductivity of Thin ZnO Films Prepared by R.F. Sputtering Technique

Abstract

AC conductivity of different thin zinc oxide films measured in the frequency range of 10 Hz to 2 MHz in the temperature interval of 300 K to 575 K is reported. ZnO films were prepared by reactive r.f. magnetron sputtering from ZnO target. The experimental data reveal that a.c. conductivity is proportional to ω^s. The value of s was found to be temperature dependent, decreases with increasing temperature. These observations suggest that correlated barrier hopping model is the most likely mechanism. The temperature dependence of a.c. Conductivity is expressed in power law form as σ(ω) ∝T ⁿ. The temperature exponent n is found to be increasing with increasing temperature and decreasing frequency in accordance with the narrow band limit. At high temperature the conductivity variation with frequency is comparatively small. The polaron binding energy (W _m), the height of Coulomb barrier (W) and the characteristic relaxation time (τ₀) have been calculated. The values of W _m and W increase as the thickness decreases whereas the values of τ₀ decrease with decreasing thickness.