Ferromagnetism of Heteroepitaxial Zn_1-xCu_xO Films Grown on n-GaN Substrates

Ferromagnetic Zn_1-xCu_xO (ZnO:Cu) films were epitaxially grown on n-GaN(0001)/Al₂O₃(0001) by radio-frequency magnetron sputtering at a substrate temperature as low as 700°C. X-ray diffraction θ-2θ scans, φ-scans, and surface morphology studies revealed the degree of crystallinity, epitaxiality, and grain size. The full-width at half-maximum of the peak for the ZnO:Cu films deposited on GaN was below 0.18° according to ω-scans. The chemical bonding states and depth profiles of the films were investigated by X-ray photoelectron spectroscopy (XPS) and with a glow discharge spectrometer (GDS). A magnetic property measurement revealed that Cu-doped ZnO films exhibit ferromagnetic behavior with a strong exchange interaction between sp-band carriers and localized d electrons at room temperature.