The Study On Electronic Structure Of SiC-based Diluted Magnetic Semiconductor By The First Principle Mathod

Diluted magnetic semiconductors have been a major topic of physics and materials science because of their potential applications as the spintronic devices such as spin field effect transistor,magnetic memory and magnetic sensor.SiC has excellent physical properties of wide bandgap,high thermal conductivity,good wearability and resistance to irradiation,so it can be a proper candidate for spintronic devices materials in the extreme conditions.By using the first-principles method based on the density functional theory,we studied the formation energies,electronic structure,and magnetic properties of polytype SiC with intrinsic Si or C vacancies,3d transition metal(TM)impurities,and rare earth Gd impurity.The main contents are as follows:(1)We calculated the formation energy,electronic structure and magnetic properties of 3C-SiC,4H-SiC and 6H-SiC with intrinsic Si or C vacancies.It is found that both Si vacancies and C vacancies can introduce defect levels within the forbidden band,and thus have an effect on the conductivity and magnetic moments of the system.The C vacancies has a lower formation energy than Si vacancies.Si vacancies can introduce the magnetic moments,whose values exhibit an increasing trend with the concentration of Si vacancies,and 12.5%Si vacancies can induce the total magnetic moment of about 4.2?_B.The divacancy V_SiV_Cintroduces the magnetic moment of about 1?_B.In contrast,the effect of C vacancies on the magnetic moment is weak.(2)We calculated the electronic structures and magnetic moments of the 3d transition metal doped 6H-SiC.The calculated results show that V,Cr,Mn,Co and Cu impurities can contribute different magnetic moments depending on their valance electrons to the semiconductor,while Fe and Ni have no contribution to the magnetic moment.However,the existence of Si or C vacancies adjacent to Fe atom can induce the Fe atom magnetic moment of about 2?_Bdue to the change of crystal field environment around Fe atom.This means that the magnetic moments in Fe-doped SiC can be produced by intrinsic Si or C vacancies that are introduced during Fe implant into SiC.(3)We also calculated the magnetic properties of Gd doped SiC and defect complexes formed by Gd and Si or C vacancies.The calculation results show that the crystal volume of the system increases after Gd doping SiC due to the larger radius of Gd than Si.Gd can introduce a magnetic moment of about 7.5?_Bderived from the half-filled 4f electrons,but Si vacancies around Gd have almost no contribution to the magnetic moment of the system.The magnetic properties of Gd-doped SiC is very different from those of Gd-doped GaN.