Study On Behavior Of Nickel Adsorption,Diffusion And Magnetism On Nitride Surface

?-nitride semiconductor material has a direct wide bandgap,good structural,chemical and thermal stability,good light transmission characteristics and low toxic,which makes it has great potential value in optoelectronic devices and spintronic material.In particular,Ni-doped ?-nitride semiconductor materials have important technical value in many fields.When Ni ions were adsorbed on the surface of nitride materials,the hole concentration of p-type nitride can be increased effectively,thereby improving the quality of LED.In addition,the transition metal Ni-doped ?-nitride semiconductor material is an important optional material for the preparation of spin electronics.However,a series of problems have to be solved on actual application.For example,the study of the interfacial contact between nitride and Ni metal is limited to experimental analysis,the mechanism of interfacial contact is rarely studied in theoretical calculation.Futhermore,it is difficult to prepare the room temperature ferromagnetic materials.The origin of the magnetism observed in diluted magnetic semiconductor?DMS?is still under debate.This dissertation focused on the most intensively investigated ?-nitride semiconductor material-AlN and AlGaN films.Theoretical and experimental researches are studied on the diluted magnetic semiconductor and the interfacial contact between AlN and nickel.The main conclusions are as follows:Study on behavior of nickel adsorption and diffusion on nitride surface is based on the first-principles plane-wave approach based on density functional theory.The results show that the most stable position of nickel adsorption on AlN?0 0 0 1?-2×2 surface is at the H3 sites,and the second location is at the T1 sites,which suggest that the AlN?0 0 0 1?surface is highly active towards the adsorption of nickel.The most stable positions of a Ni adatom on GaN?0001?are at the H3 sites and T4 sites,for low?0.25-0.5?and high?0.75-1?Ni coverage respectively.Ni ions were implanted into AlN and Al_0.5Ga_0.5N films.From XRD?XPS and VSM measurements,we can find that nickel is at the interstitial site in AlN and Al_0.5Ga_0.5N films before annealing.The films were annealed at 900 K in the furnace for the transference of Ni ions from interstitial sites to substitutional sites and activating the Ni³⁺ions.The apparent hysteresis loops prove the films exhibited magnetism with Curie temperature above 300K.Above these samples,Ni-doped AlN film has the higher magnetization intensity and Ni-doped AlGaN film has the lower coercive force.We indicate that both Ni-doped AlN material and Ni-doped AlGaN material are promising dilute magnetic semiconductors and have potential applications in the field of spintronics.Structure and magnetic characteristics of Ni-doped AlN and Ni-doped AlGaN are calculated and analyzed using the first-principles plane-wave approach based on density functional theory.The result shows that the density of the main spin and the minor spin near the Fermi level do not completely coincide,which produces the magnetic properties.From the first-principles calculation,we found Ni-doped AlN and Ni-doped AlGaN have apparent magnetism.A majority of the magnetic moments are contributed by the NiN₄tetrahedron.The doped Ni atom hybridizes with its four nearby N atoms in NiN₄tetrahedron,then N atoms are spin polarized and couple with Ni atom.These characteristics manifest a very strong hybridization between Ni atom and four nearby N atoms in NiN₄ tetrahedron.The p-d exchange mechanism between Ni-3d and N-2p can be the theoretical basis for the origin of the magnetism.