P掺杂4H-SiC超晶胞的第一性原理计算

First-principles calculations of P doped 4H-SiC supercell

采用基于密度泛函理论的第一性原理平面波超软赝势方法,计算本征以及P替位式掺杂,P间隙式掺杂4H-SiC的晶格常数、能带结构、态密度、载流子浓度和电导率。结果表明:P掺杂减小了4H-SiC的禁带宽度,其中P替位C原子掺杂的禁带宽度最小。替位式掺杂导致4H-SiC的费米能级进入导带,使其成为n型半导体,间隙式掺杂使4H-SiC的费米能级接近导带并在其禁带中引入杂质能级。替位式掺杂后,4H-SiC的自由电子主要存在于导带底,而间隙式掺杂4H-SiC中除了导带底外,禁带中的杂质能级也提供了自由电子,因此,电子浓度大幅度增加。掺杂4H-SiC的载流子迁移率主要由中性杂质对电子的散射决定,较本征态的大幅度降低。通过计算4种体系的电导率可知,P替位Si原子掺杂4H-SiC的电导率最大,导电性最好。

The lattice parameters, band structures, density of states, carrier concentrations and electrical conductivities of pure 4H-SiC, P substitutional doped, and P interstitial doped 4H-SiC were calculated using the plan-wave ultra-soft pseudo-potential method based on the density functional theory. The results indicate that the P doping decreases the forbidden band widths of 4H-SiC, and the P substituted for C doped 4H-SiC shows the narrowest band gap. Substitutional doping makes the Fermi energy level introduces into the conduction band of 4H-SiC, and the 4H-SiC becomes an n-type semiconductor. Interstitial doping makes the Fermi energy level near the conduction band of 4H-SiC and introduces impurity energy levels into the forbidden band. The electrons of substitutional doped 4H-SiC mainly exist at the bottom of the conduction band. While the impurity energy levels in the forbidden band also provides electrons except those existing at the bottom of the conduction band of interstitial doped 4H-SiC, so, the electron concentration increases significantly. The carrier mobility of the doped 4H-SiC is mainly depending on the neutral impurity scattering and decreases significantly comparing to the intrinsic state. Through the calculations of the electrical conductivities of the four systems, it is found that the electrical conductivity of 4H-SiC with P substituted for Si is the biggest, and the 4H-SiC shows the best conductivity.