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

Abstract

The structural, valence of elements and magnetic characteristics of Ni-implanted Al0.5Ga0.5N films, deposited on Al2O3 substrates by metalorganic chemical vapor deposition (MOCVD), were reported. Ni ions were implanted into Al0.5Ga0.5N 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 Ni3+ 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 Al0.5Ga0.5N films and the chemical bonding states of Ni3+ is Ni–N. The apparent hysteresis loops prove the films exhibited ferromagnetism at 300 K. The room temperature (RT) Ms and Hc 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 NiN4 tetrahedron, 2.38 μB, makes the primary contribution. The doped Ni atom hybridizes with its four nearby N atoms in NiN4 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 Al0.5Ga0.5N films can make it possible to the applications for the spin electric devices.