Investigation Of The Structure And Conductivity Of Defected Si And SiC By Using First-principles Calculations

With the development of information science, the microelectronics industry based on semiconductor material has become a pillar industry in national economy, which plays an important role in the national economy and modernization of national defense. Silicon, as the most important of the first generation semiconductor material, occupies a dominant position in the field of semiconductor materials. SiC has a wide range of applications for its characteristics of wider band gap, high critical breakdown field, high electron mobility, and strong resistance to radiation. There are a large number of high-energy nuclear radiation particles and photons in the space radiation. Therefore, the crystal structures will be damaged, which results in the invalidation of some electronic systems. In this work, the first-principle package (VASP) based on the density functional theory (DFT) is used to study the electronic structures, intrinsic oxygen, strontium and titanium vacancies.The main contents are as the follows:1. The geometric and electronic structures of Si, 3C-SiC,4H-SiC are calculated systematically, including the crystal structure, band structure, density of states.2. The crystal structure, band structure, density of Si is calculated with different number of defects. We find that some defect bands appear in the band gap when the Si crystal has defect, and the defect bands increase with the number of defects, which causes the DOS changes greatly around the Fermi level. In addition, the carrier mobility of Si is calculated.3. The structural characteristics and electronic properties of 4H-SiC are studied systematically. The results show that some defect bands appear in the band gap when the 4H-SiC crystal has defect. When the vacancy occupies C position, the defect levels are near the conduction band; when the vacancy occupies Si position, the defect levels are near the valence band.4. The magnetic properties of wide band gap semiconductor 3C-SiC doped with 3d-transition metals (TM=V,Cr and Mn) are calculated by means of first-principle. The results show that V,Cr and Mn atoms are tend to substitute Si site of 3C-SiC compared with C site. The Cr doped 3C-SiC system exhibits more stable ferromagnetism compared with V and Mn doped system in same doping concentration. Therefore, the Cr is chosen as the candidate element for doping. The band gap and ferromagnetism of 3C-SiC becomes smaller and weaker with the increase of doping concentration. Finally, the ferromagnetism origin mechanism of Cr doped 3C-SiC is explained according to the density of states (DOS), which indicates that the ferromagnetism results from the exchange splitting of Cr-3d state.