Enhancement of room temperature ferromagnetism in Cu-doped AlN thin film by defect engineering

Cu-doped AlN thin films were deposited by reactive magnetron co-sputtering at room temperature. The results showed that all the Cu-doped AlN films exhibited room-temperature ferromagnetism (RTFM). The results also showed that when the Cu-doping content was at 4 at.%, the maximum atomic magnetic moment (AMM) was about ∼0.6 μB/Cu. Raman and X-ray absorption spectroscopy showed that large numbers of N-related defects existed in Cu-doped AlN films, which was ascribed to its intrinsic RTFM. Moreover, to verify the role of defects on the RTFM of Cu-doped AlN films, defects were artificially introduced into Al0.96Cu0.04N films by carbon implantation. After carbon implantation, the AMM was significantly enhanced to ∼2.5 μB/Cu. After examination and discussion of the results, we believed that C-N compounds were formed as carbon implantation, which consumed part of the available nitrogen and then increased the density of N-related defects in Al0.96Cu0.04N films. This is favorable for coupling among bound magnetic polarons (BMP). Therefore RTFM is strongly correlated to engineered defects in Cu-doped AlN films. These results promote a viable route to enhance the RTFM of III-nitrides dilute magnetic semiconductors via defect engineering.