Al-N共掺杂3C-SiC介电性质的第一性原理计算

采用基于密度泛函理论的第一性原理平面波超软赝势法,建立了未掺杂,Al,N单掺杂和Al-N共掺杂3C-SiC的4种超晶胞模型,并分别对模型进行了几何结构优化,对比研究了其能带结构,态密度分布和介电常数.计算结果表明:Al掺杂会增大SiC的晶格常数,而N对SiC的晶格影响很小.Al掺杂会导致费米能级进入价带,使3C-SiC成为p型半导体,且带隙宽度略为加宽.N掺杂后的SiC其导带和价带均向低能端发生移动,带隙稍有减小.本征3C-SiC几乎不具备微波介电损耗性能.但是可以通过进行Al掺杂或N掺杂加以改善,Al掺杂后的效果尤为突出.计算发现Al-N共掺杂后的3C-SiC材料在8.2—12.4 GHz范围内其微波介电损耗性能急剧下降,与实验结果相符合,并对这一结果进行了讨论分析.

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.
Keywords： Al-N codoped 3C-SiC dielectric properties first principles