Density Functional Theory Study Of Heterojunction In 3C-SiC/6H-SiC System

As one of typical representative in the third generation semiconductor materials, SiC occurs in over 200 polytype, among which the ideal lattice match of 6H-SiC(0001)and 3C-SiC(111), and the relatively low thermal mismatch, make 3C-SiC/6H-SiC heterojunction an adequate choice for 3C-SiC/6H-SiC heterojunction photoconductive switch.In order to make a research on the characteristics of 3C-SiC/6H-SiC heterojunction, the structural and electrons properties of 3C-SiC/6H-SiC heterojunction are study by first-principle calculations. Firstly, the band structure and the density of state of the 3C-SiC and the 6H-SiC bulk structure were obtain by plane-wave pseudopential method within the framework of density functional theory respectivly. The result shows that both of the bulk crystals have indirect band gaps. The top of the valence band in two cases is at the G point and the bottoms of the conduction band are at different locations. The density of state calculated from these two structure show that the C-2p and Si-3p orbital have strong hybridization effect.Secondly, the Si-face surface system of 3C-SiC in <111> direction is calculated. The result shows that the Fermi level enters into the conduction band, and after relaxation the band structure receives subtle changes. For the 6H-SiC surface system, the study here is <0001> direction of C-face. The calculation of the density of states tells that the valence band of this surface system tends to move to the lower energy area after relaxation.Finally, with the Materials Studio software, the 3C-SiC/6H-SiC heterojunction is constructed, and an analysis is made to the 3C-SiC/6H-SiC heterojunction after geometry optimized. The result shows that the heterojunction has indirect band gap. The top of the valence band is at the G point and the bottom of the conduction band is at the F point. The distribution of density of states at the interface shows that there is no density peak at Fermi level. At the same time the band offset of 3C-SiC/6H-SiC heterojunction is obtained, which the valence band offset and conduction band offset are about 0.0912eV and 0.7212eV respectively.