Effect of Mn doping on the electric and dielectric properties of ZnO epitaxial films

Abstract

The Mn doping effects on the electric and dielectric properties of ZnO epitaxial films were studied. To optimize the stoichiometry of undoped ZnO film prepared by pulsed laser deposition, we evaluated the intensity ratio of the optical emission from excited oxygen atoms (O*) and excited zinc atoms (Zn*) generated by ablating a ZnO ceramic target in plume. The leakage current of undoped ZnO film decreased with an increase of the ratio I(O777*)∕I(Zn335*). Mn doping of ZnO was also effective in decreasing the leakage current. The ZnO:4at.% Mn had a very small leakage current, eight orders of magnitude less than that of undoped ZnO. With a Mn concentration above 4at.%, on the other hand, the leakage current was increased. The activation energy in ZnO:Mn obtained from the temperature dependence of the ac conductivity revealed that oxygen vacancy was responsible for the large current at the Mn concentration below 2at.%. For the sample with the Mn concentration of 2–3at.%, dominant conduction in ZnO:Mn epitaxial films originated from the interstitial Zn. When the Mn concentration was above 4at.%, the conduction was governed by the substitution of Zn atoms in the oxygen site. Impedance analysis revealed that the origin for large resistivity of ZnO:Mn films was not the ZnO/electrode interface but the bulky part of the films.