Role of nitrogen split interstitial defects in the magnetic properties of Cu-doped GaN

Cu-doped GaN thin films are grown by plasma-assisted molecular beam epitaxy. With nitrogen plasma only, films phase segregate into GaN and Cu-rich alloys. In contrast, when nitrogen-hydrogen plasma is used, the films are single-phased Ga _1-xCu _xN, with x as high as 0.04. Contrary to earlier studies, however, these films are not ferromagnetic, but rather paramagnetic in nature. First-principles calculations indicate that although each substitutional Cu _Ga exhibits a moment of 1 μ _B/Cu, it can be suppressed by neighboring intrinsic defects such as N split interstitials.