First principles calculation of dielectric properties of Al and N codoped 3C-SiC

We have performed geometry optimizations of crystal structure and contrasted the calculated results of band structure, density of states, and permittivity of 3C-SiC for four kinds of doped supercell models: undoped, Al-doped, N-doped and Al-N codoped ones, by using the first principles plane wave ultrasoft pseudopotential method based on the density functional theory. Results show that Al doping increases the lattice constant of 3C-SiC, while N doping has little effect on the SiC lattice. The Fermi energy level introduced into valence band and the band gap is slightly widened through Al doping for 3C-SiC, and the SiC becomes a p-type semiconductor. Both the conduction band and the valence band of N-doped SiC move toward low energy side, and its band gap is slightly reduced. Intrinsic 3C-SiC has shown poor dielectric loss properties in the microwave range, but the dielectric property can be improved significantly through the Al doping or N doping, especially the former. The microwave dielectric loss performance of 3C-SiC doped with Al and N in the range of 8.2-12.4 GHz declined sharply, which validates the results of experiments. We finally analyzed and discussed the reason for the decrease of permittivity.