Influence of N₂ gas flow on the high-frequency magneto-electrical properties of ZnO thin films

Undoped and N-doped ZnO (ZnO:N) thin films were prepared with different N₂ flow rates on Al₂O₃ substrates by rf magnetron sputtering methods. The structure and high-frequency magneto-electrical properties of the ZnO:N films varied drastically with the variation of N₂ flow rate. With the introduction of N₂ gas during deposition, short hexagonal-like nanorods grown at grain surface were observed. In comparison with the undoped ZnO film, Raman spectra of the ZnO:N films revealed four anomalous peaks at 276, 510, 586 and cm^-1, which are attributed to nitrogen-related defect complexes. Complex impedance spectra of all the films were analyzed by an equivalent circuit, employing two sets of parallel resistance and capacitance components in series to represent the oxide grain and grain boundary contributions, respectively. The analyzed results have implied that the N₂ flow rate can effectively alter the defect concentration of the films, and consequently adjust the ac conductivity, magneto-dynamical and dielectric relaxation behaviors of the oxide-based magnetic semiconductor polycrystalline films.