First Principles Study Of N Doped 4H-SiC

The density function theory in generalized gradient approximation is used in this paper to analyse some properties of N-doped 4H-SiC by first principles method. The difference between undoped and N-doped 4H-SiC on formation energy, band structure, density of state and optical properties are calculated and analysed in this paper.There are two kind of place where nitrogen can substitute carbon in 4H-SiC, c and h. The calculation result shows that the formation energy of c is slightly lower than that of h, which leads to the density of c could be just slightly higher than that of h, without great difference. The result also show that the density of N is much higher under Si-rich experiment condition than C-rich experiment condition.N is a shallow donor in 4H-SiC by comparing the band structure and density of state between N-doped and undoped 4H-SiC. N-Doping will induce band gap narrowing, this is mainly because the conduction band shift to valence band. This narrowing could be explained by the strength of N-Si bond is weaker than that of C-Si bond, so the electric gas overlaps less.4H-SiC is a promising photoelectric material, so its optical properties is also studied. Our calculation shows that N-doping will induce new absorption peak appears at both parallel to c-axis and perpendicular to c-axis. But there is only one peak perpendicular to c-axis, however, it's two when parallel to c-axis. These will result in the limit of 4H-SiC in infrared wave-length. On the other hand, the high energy part of absorption spectrum shifts to the lower-end. This means there will be a greater window for N-doped 4H-SiC than undoped and doped one could be used in a larger wave-length than undoped one.