First-Principles Study On Electronic Structure And Physical Properties Of SiC Material Doped With Semi-Additives

With the superior semiconductor features, SiC become the core materials of the third generation semiconductor. With the rapid development of semiconductor devices, the performance of pure semiconductor materials couldn’t satisfy the request of the practical application, so the doping method very effective means of widening the application of SiC material. Therefore, in recent years, the study of the doping intrinsic SiC matter is more valued by science researchers.In this paper, by the first-principles calculation method based on density functional theory, we study the doping samples respectively taking 3C-SiC and 4H-SiC as intrinsic substance. By doping the elements B(Ⅲ), Al(Ⅲ), Ga(Ⅲ), N(Ⅴ), P(Ⅴ), and As(Ⅴ), we achieved the p-type doping and the n-type doping of the 3C-SiC and 4H-SiC. We respectively analyzed and discussed how the two kinds of doping do effect on the band structure, electronic density of states,population analysis, dielectric constants and elastic properties of the doped system.The main results are as follows:Firstly, when 3C-SiC was the intrinsic substance, the forbidden band width of the intrinsic3C-SiC was 1.424 eV in calculation. With the doping of B(Ⅲ), Al(Ⅲ), and Ga(Ⅲ), the forbidden band width of the system increased, and the doped system showed the characteristic of the direct band gap. The transition type of the doped 3C-Si C changed from the indirect type to the direct type and the doping atoms made the Fermi level through the valence band, so that 3C-Si C expressed the characteristics of p-type semiconductor; with the doping of N(Ⅴ), P(Ⅴ), and As(Ⅴ),the doping of P and As both made the forbidden band width of 3C-SiC larger except the doped system of N. And the doping atoms all made their Fermi level through the conduction band, so that3C-SiC expressed the characteristics of the n-type semiconductor. Through the calculation and analysis of dielectric constant, we found that whether it was p-type doping or n-type doping, the static permittivity of the doped system increased averagely. By elastic properties analysis, we knew that whether it was p-type doping or n-type doping, the bulk modulus and shear modulus of the doped system had different degrees of reduction.Secondly, when 4H-Si C is the intrinsic substance, the forbidden band width of the intrinsic4H-SiC was 2.282 eV in calculation. With the doping of B(Ⅲ), Al(Ⅲ), and Ga(Ⅲ), after the geometric optimization, the doped system was discovered different degree of lattice distortion, and the forbidden band width of the system decreased. It had become the semiconductor material of indirect band gap, and the Fermi level are all through the valence band, so that 4H-SiC expressed the characteristics of p-type semiconductor; With the doping of N(Ⅴ), P(Ⅴ), and As(Ⅴ), The forbidden band width of the doped system was smaller than it in intrinsic 4H-SiC, the transition type of band had changed from the indirect type to the direct type. The doping elements such as N,P, as provided a large number of relatively free electronic as carrier in the bottom of the conduction band, and they formed a donor level. The Fermi level could through the conductionband, so that 4H-SiC expressed the characteristics of the n-type semiconductor; According to the analysis of permittivity, we could know that whether p-type doping or n-type doping, there is little numerical difference between the static permittivity of the doped system and that in the intrinsic4H-SiC. By the elastic properties analysis, we could know that whether it is p-type doping or n-type doping, the shear modulus of the doped system was always reduced, but when it was in N doping system and P doping system, the volume modulus increases slightly, the volume modulus in the other doped system are all decreasing.