二维GaN中带电缺陷性质的第一性原理研究

The properties of charged impurities in two-dimensional GaN:a first-principles calculation

带电缺陷形成能与电荷转移能级对探索材料中n-type或p-type掺杂具有重要指导意义.基于第一性原理方法,本文结合二维带电缺陷校正理论,将半局域泛函电荷转移能级有效转换到杂化泛函精度,对六方二维氮化镓(Hexagonal gallium nitride,h-_(Ga)N)12种n-type和p-type带电掺杂体系结构性质、磁学性质及缺陷性质进行系统研究.n-type体系包括C_(Ga),Si_(Ga),Ge_(Ga),O_(N),S_(N),Se_(N),p-type体系包括Be_(Ga),Mg_(Ga),Ca_(Ga),C_(N),Si_(N),Ge_(N),结果表明Ge_(Ga)和Be_(Ga)分别是n-type和p-type中最稳定缺陷.n-type体系最稳定价态为0和1+价,施主离子化能分布在低于导带底~0.4到~0.6 eV能量区间,表现为深施主能级特性,会捕获p型h-GaN中空穴,影响空穴导电率;p-type体系最稳定价态为1-,0(Ge_(N)除外),1+价,受主离子化能分布在高于价带顶~1.25到2.85 eV能量区间,表现为深受主能级特性,会捕获n(p)型h-GaN中电子(空穴),影响n(p)载流子导电率.研究结果表明,二维h-GaN体系很难通过单缺陷实现n或p-type掺杂,实验上需要考虑复合缺陷实现双极型掺杂.

The calculation of charge transition energy level(CTL)and defect formation energy are of significant importance for exploring potential n-type or p-type doping in materials.Based on the first-principles method,combined with the theory of two-dimensional charged defect correction method,as well as effectively convert the semi-local functional results of CTL to hybrid functional accuracy,this paper systematically studied 12 kinds of n-type and p-type substitute dopants in the two-dimensional hexagonal gallium nitride(h-GaN)system.Among which n-type doping includes C_(Ga),Si_(Ga),Ge_(Ga),O_(N),S_(N),Se_(N) and p-type doping includes Be_(Ga),Mg_(Ga),Ca_(Ga),C_(N),Si_(N),Ge_(N).The results show that the most stable charge states for n-type system are 0 and 1+,and the donor ionization energy is distributed in the energy range of~0.4 to~0.6 eV lower than the conduction band minimum(CBM),characterized as deep donor energy level,which will capture the holes in p-type h-GaN and affect the hole conductivity.The most stable charge state of the p-type system is 1-,0(except for Ge_(N)),and 1+,and the accetpor ionization energy is distributed in the energy range higher than the valence band maximum(VBM)~1.25 to 2.85 eV,characterized as deep acceptor energy level,which will capture electrons(holes)in n(p)h-GaN and affect the conductivity of n(p)carriers.In Conclusion,it is difficult for two-dimensional h-GaN system to achieve n or p-type doping through single defect,and it is necessary to consider the complex defects to achieve bipolar doping experimentally.