Electronic Structure And Magnetism Of SiC-based Ferromagnetic Semiconductors

Spintronics,also known as magnetic electronics,is a combination of magnetic and microelectronics interdisciplinary.Diluted magnetic semiconductor,utilizing both charge and spin properties of electrons,shows enough electron transport properties and magnetic memory characteristics of semiconductor materials combined with excellent magnetic,magneto-optical,magnetic properties.Silicon carbide(SiC),a wide band gap semiconductor material,represents great potential of the third generation of semiconductor material.It shows many excellent physical properties,has broad applications in high-temperature,high-frequency,high-power,optoelectronic devices and radiation microelectronic devices.By pseudopotential plane wave method based on first-principles density functional theory,using CASTEP code in Materials Studio 5.0 package,the lattice constant,electronic structure and magnetic properties of 2H-SiC,3C-SiC,4H-SiC,6H-SiC were studied.The results provide a theoretical basis and important reference for experiments.The specific contents are shown as follows:The crystal structure,energy band structure and density of states of the 2H-SiC,3C-SiC and 6H-SiC system were studied.Systematic study on the magnetic material of A1 doped,Vsi and Vc doped 6H-SiC were performed,the reasons for the existence of magnetism were analyzed.The results show that 2H-SiC and 6H-SiC are indirect band gap semiconductor materials,3C-SiC is a direct band gap semiconductor material.Vsi doped 3C-SiC is a magnetic system,which was mainly produced by Si-3p orbital electrons and C-2p orbital electron hybridization.Al doped 3C-SiC system did not produce any magnetism;A1 and vacancies co-doped 6H-SiC is a magnetic system;Vc or Vsi doped 6H-SiC produced a weak magnetism,While Vsi and Vc co-doped 6H-SiC shows obvious magnetism,which mainly due to the introduction of Vsi;A1 doped 6H-SiC system did not produce magnetic memory,Al and Vsi co-doped 6H-SiC system presents the magnetism,The magnetic moments is not from Al-3p orbits but mainly from C-2p polarization.We calculated the electronic structure and magnetic properties of the Cr doped 4H-SiC,Al,Fe and Al,Mn co-doped 4H-SiC system.For Cr 4H-SiC doped System,Cr3+ ions replace Si4+ ions,The hole was introduced to the system,resulting in 2.40?B spin magnetic moment,The magnetic moment is mainly provided by local doping Cr atoms.Ferromagnetic state in Cr-doped 4H-SiC system is stable.Two Cr atoms were coupled by Cro:3d-C:2p-Cr1:3d chain and the carrier exchange mechanism played a key role.The results show that the energy difference between the ferromagnetic state and non-ferromagnetic state in Cr-doped 4H-SiC system is large,indicating that Cr doped 4H-SiC is a promising spintronic materials.In A1 and TM(TM=Fe,Mn)co-doped 4H-SiC system,the formation energies of 14 possible configurations were calculated and the most stable structures were determined.Al atoms did not produce any spin polarization,and Al,TM co-doped system produced spin polarization,The whole system more inclined to be the ferromagnetic state,TM-3d orbital electrons and C-2p orbital electrons hybrid,leading to the formation of a TM:3d-C:2p-TM:3d chain,which indirectly promote the ferromagnetic coupling.The electronic structure and magnetic properties of N and Vsi co-doped 4H-SiC system were studied by using first-principles calculations.N or Vsi doping did not produce spin polarization,while co-doped system generates spin polarization.The magnetic coupling calculation results show that ferromagnetic state and antiferromagnetic state compete with each other in N and Vsi co-doped 4H-SiC system under different charge(0,-1,-2).Introduction of Si-2p vacancy makes spin polarization of C-2p orbital and N-2p orbital,the coupling between two C atoms produce ferromagnetic properties.