Intrinsic defects responsible for the anomalous Raman peaks and the room-temperature ferromagnetism in nitrogen-doped ZnO thin films

Abstract

This work aims to investigate the intrinsic defects responsible for the anomalous Raman peaks and the room-temperature ferromagnetism in the nitrogen-doped ZnO (ZnO:N) thin films deposited using a magnetron sputtering method. The X-ray diffraction results indicate that all of the films are grown with a highly c-axis-oriented wurtzite structure. All photoluminescence spectra exhibit an intensive broad band centered at approximately 3.2eV as well as a weak band at approximately 2.2eV. By using a multi-peak fitting method, we deduce that the zinc vacancies, the zinc interstitials, and the substituted nitrogen at the oxygen site are responsible for the emissions embedded in the intensive broad band, while the oxygen vacancies and the oxygen interstitials are responsible for the weak band. These defects in the ZnO:N films may be associated with the four anomalous Raman peaks at approximately 277, 511, 584 and 644cm−1. Room-temperature ferromagnetism has been observed for all of the ZnO:N films. With an increase in film thickness, the saturation magnetization first decreases rapidly and then increases. A close relationship between the saturation magnetization and the relative change in the c-axis lattice constant is observed.