Magnetic properties of Cu-doped GaN grown by molecular beam epitaxy

Abstract

Cu-doped GaN films were epitaxially grown by molecular beam epitaxy on $C$-plane sapphire substrates with an AlN buffer layer. Growth under metal-rich and nitrogen-rich conditions was investigated for different Cu-to-Ga beam-equivalent-pressure ratios ${x}_{\mathrm{BEP}}$. The samples were characterized by scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction. Films within a narrow range of ${x}_{\mathrm{BEP}}$ around 1$%$ exhibit ferromagnetic behavior with a Curie temperature higher than 400 K. For higher ${x}_{\mathrm{BEP}}g1%$, islands of a Cu-Ga compound are predominantly formed at the surface as nonferromagnetic precipitates. Our detailed study shows that the saturation magnetization of ferromagnetic films with ${x}_{\mathrm{BEP}}\ensuremath{\approx}1%$ decreases with increasing film thickness. This suggests that the ferromagnetism arises from defects, such as threading dislocations, created by the incorporation of Cu into the GaN.