HOPPING CONDUCTION IN INSULATING RF-SPUTTERED ZINC-OXIDE FILMS

The dielectric constant and ac conductivity of rf-sputtered insulating zinc oxide films has been measured in the metal-insulator-metal confi guration over a wide temperature (90-500 K) and frequency (0.1-100 KHz ) range. The films sputtered from oxide targets in argon were c-axis o riented having a resistivity of similar or equal to 10(12) Omega cm. T he dielectric constant shows a strong frequency dispersion at temperat ures above 330 K which is the intrinsic behavior of the films. The die lectric dispersion data has been fitted to (i) Debye-type relaxation ( with a distribution of relaxation times), (ii) a random-free-energy-ba rrier model (which assumes that for hopping conduction, the dielectric dispersion is correlated to the de conductivity), and (iii) the diele ctric modulus (which assumes that microscopic inhomogeneities and the distribution of conductivity relaxation times is responsible for diele ctric dispersion). The origin of dielectric dispersion has been discus sed in the light of these models. It has been found that hopping condu ction dominates in ZnO films up to 450 K.