Diluted magnetic characteristics of Ni-doped AlN films via ion implantation

Abstract

The structural and magnetic properties, as well as the mechanism of magnetization, of Ni-implanted AlN films were studied. AlN was deposited on Al₂O₃ substrates by metalorganic chemical vapor deposition (MOCVD), and subsequently Ni ions were implanted into the AlN films by Metal Vapor Arc (MEVVA) sources at an energy of 100 keV for 3 h. The films were annealed at 900°C for 1 h in the furnace in order to transfer the Ni ions from interstitial sites to substitutional sites in AlN, thus activating the Ni³⁺ ions. Characterizations were performed in situ using X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and vibrating sample magnetometry (VSM), which showed that the films have a wurtzite structure without the formation of a secondary phase after implanting and annealing. Ni ions were successfully implanted into substitutional sites of AlN films, and the chemical bonding states are Ni-N. The apparent hysteresis loops prove that the films exhibited magnetism at 300 K. The room temperature (RT) saturation magnetization moment (M_s) and coercivity (H_c) values were about 0.36 emu/g and 35.29 Oe, respectively. From the first-principles calculation, a total magnetic moment of 2.99 μB per supercell is expected, and the local magnetic moment of a NiN₄ tetrahedron, 2.45 μB, makes the primary contribution. The doped Ni atom hybridizes with four nearby N atoms in a NiN₄ tetrahedron; then the electrons of the N atoms are spin-polarized and couple with the electrons of the Ni atom with strong magnetization, which results in magnetism. Therefore, the p-d exchange mechanism between Ni-3d and N-2p can be the origin of the magnetism. It is expected that these room temperature, ferromagnetic, Ni-doped AlN films will have many potential applications as diluted magnetic semiconductors.

Keywords

III-V nitrides / metalorganic chemical vapor deposition (MOCVD) / diluted magnetic semiconductors / first-principles

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Acknowledgements

This work was supported by the National Key R&D Program of China (Nos. 2016YFB0400901, and 2016YFB0400804), the Key Laboratory of Infrared Imaging Materials and Detectors, Shanghai Institute of Technical Physics, Chinese Academy of Sciences (No. IIMDKFJJ-15-07), the National Natural Science Foundation of China (Grant Nos. 61675079, 11574166, and 61377034), and the Director Fund of WNLO.

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