Inspection of magnetic semiconductor and clustering structure in CoFe-doped ZnO films by bias-dependent impedance spectroscopy

Diluted magnetic semiconductor and cluster dominated structure of CoFe-doped ZnO films have been systematically investigated by bias-dependent impedance spectroscopy. The complex impedance spectroscopy of 5 mol % CoFe-doped ZnO film can be fitted by an equivalent circuit employing two sets of parallel resistance (R) and capacitance (C) components in series, representing the oxide grain and grain boundary contribution, respectively. For 10 mol % CoFe-doped ZnO film, a third RC component together with a single resistance element, which are likely due to the presence of metal clusters and metal-oxide interface, have to be taken into account to fit the impedance spectroscopy. By applying a dc bias of 0∼1.5 V, the relaxation contribution from different structural origin can be clearly identified. The bias-dependent impedance spectroscopy demonstrates significant sensitivity to the formation of CoFe clusters in ZnO.