Investigation of structure and magnetic characteristics of Ni-implanted AlGaN films

摘要

The structural, valence of elements and magnetic characteristics of Ni-implanted Alo.5Gao.5N films, deposited on AI_2O_3 substrates by metalorganic chemical vapor deposition (MOCVD), were reported. Ni ions were implanted into Alo.5Gao.5N films by Metal Vapor Arc (MEVVA) sources under the energy of 100 keV for 3 h. The films were annealed at 900 K in the furnace for the transference of Ni ions from interstitial sites to substitutional sites in AlGaN and activating the Ni~(3+) ions. Characterizations were carried out in situ using X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS) and Vibrating sample magnetometer (VSM), indicating that the films have wurtzite structure without forming a secondary phase after annealing. Ni ions were successfully implanted into substitutional sites of Alo.5Gao.5N films and the chemical bonding states of Ni~(3+) is Ni-N. The apparent hysteresis loops prove the films exhibited ferromagnetism at 300 K. The room temperature (RT) M_s and H_c obtained were approximately 0.22 emu/g and 32.97 Oe, respectively. From the first-principles calculation, A total magnetic moment of 2.86 μB per supercell is calculated: the local magnetic moment of NiN_4 tetrahedron, 2.38 μB, makes the primary contribution. The doped Ni atom hybridizes with its four nearby N atoms in NiN_4 tetrahedron, then N atoms are spin polarized and couple with Ni atom with strong magnetization, which result in ferromagnetism. Therefore, the p-d exchange mechanism is responsible for ferromagnetism in Ni-doped AlGaN. It is expected that the room temperature ferromagnetic Ni-doped Al_(o.5)Ga_(o.5)N films can make it possible to the applications for the spin electric devices.