First-principles Investigation On The Defects At SiC/SiO₂ Interface

As a wide bandgap semiconductor material,SiC material has received extensive attention from the semiconductor industry and scientists,especially in the contemporary era where Si-based devices is gradually reaching the physical limit.The mobility of SiC devices is very low,mainly due to the extremely high interface state at the SiC/SiO₂ interface,which makes SiC-based MOS devices and other devices containing SiC/SiO₂ interface performance is adversely affected.When high near-interface defects are present in the MOS structure,traps are generated,which trap carriers and increase electron scattering.As a result,the channel electron mobility of the device decreases,and the device performance is affected.In order to improve the device performance,more and more researchers in recent years began to pay attention to the effects of defects on the electronic state at the SiC/SiO₂interface.Previous studies on the electronic states of defects in SiC have been conducted,but the research on the interface with SiC/SiO₂ is not comprehensive enough.In this paper,by studying the point defects at the SiC side near the interface,the influence of defects at the interface on the electrical properties is obtained.It allows us better understand the origin of the interface state that we investigate the principle of defects affecting the electrical properties at the interface,and help to design further propose experiment for improving the interface state,which lays the foundation for improving the performance of SiC devices.In this paper,four kinds of defect-related interface structures are mainly studied through simulation calculations.Following defects are included,Si vacancy,C vacancy,double vacancy and antisite pair.Since the type of contact surface with the oxide layer affects the role of defects at the interface,the Si contact surface structure and C contact surface are particularly distinguished in the research process.Using the first-principles related calculation theory,through the Material Studio software package,we constructed the SiC/SiO₂ interface structure.Calculation results is demonstrated as follows.When Si vacancies,C vacancies,double vacancies,and antisite pair exist at the SiC/SiO₂ interface,a large number of density of state occurs in the band gap,resulting in specific defect levels.The defect states are analyzed by density of local states.It shows a strong correlation with some atoms around the defect,and the Fermi level at the interface also shifts after the defect is introduced.These defect levels capture carriers in the form of traps,which will reduce the carrier concentration near interface,and thus the carrier mobility is affected.The results of the sub-contact surface discussion show that in the Si-contact surface structure,defects in first lattice position only cause the atoms near the defect position to undergo a dramatic change in the density of states,but the effects of atoms farther from the defect are Very small.In the C-contact surface structure,the defect of a certain lattice position and atoms near the defect position have a great change in their density of states,the double vacancies and antisite pair under the C-contact surface also have a great influence on the C atom layer on the contact surface.However,the impact on other positions that are farther away from the defect is very small.Finally,the density of states of our structure is analyzed by sub-orbital.There is a great change in the defect level at the 2p orbit.For vacancy defects,these outermost electrons do not form a covalent bond with any other atom.In the form of dangling bonds,these dangling bonds generate defect levels that impede the movement of carriers.For double vacancies and antisite pair,the existence of defects makes the interface also produce the density of states,affecting the original stable density of state distribution and the introduction of defects from the structure diagram and subatomic analysis,we believe that the appearance of defects makes the outermost layer of the C atom of the interface.It is generally affected by the originally stable covalent bond in the system,which resulted in the density of state in the forbidden band and brought new defect energy levels.