Microstructures, electrical and magnetic properties of (Ga, Co)-ZnO films by radio frequency magnetron co-sputtering

In this study, [Co0.05GaxZn(0.95 − x)O] films with different Ga contents were co-sputtered on glass substrates by rf magnetron sputtering. The content of Co in the films was fixed at ~ 5 at.%. The content of x [Ga/(Ga + Co + Zn)] varied from 0 to 3.2 at.%. As analyzed by Hall effect measurement, the resistivity (ρ) of the film is 42.90 Ω·cm when x content is 0. When the content of x increases to 3.2 at.%, the ρ value drops greatly to 4.93 × 10− 3 Ω·cm. It is found that both the surface roughness and grain size of columnar (Ga, Co)-ZnO films decrease significantly after Ga addition into the films, but the phase structure remains almost unchanged. In magnetic properties analysis, two distinct mechanisms of bound magnetic polaron and carrier-mediated exchange lead to the films presenting different ferromagnetic behaviors in various carrier density regions.