氮缺陷对GaN/g-C3N4异质结电子结构和光学性能影响的第一性原理研究

基于密度泛函理论下的第一性原理平面波超软赝势方法，研究了单层GaN、g-C₃N₄、GaN/g-C₃N₄异质结及3种氮缺陷GaN/g-C₃N₄-V_XN （X=1、2、3）异质结的稳定性、电子结构、功函数及光学性能。计算结果表明，GaN/g-C₃N₄异质结体系晶格失配率极低（0.8%），属于完全共格。与单层g-C₃N₄相比，GaN/g-C₃N₄和GaN/g-C₃N₄-V_XN （X=1、2、3）异质结的导带向低能方向偏移，价带上移，从而导致带隙减小，且态密度均显示出轨道杂化现象。GaN/g-C₃N₄和GaN/g-C₃N₄-V_XN （X=1、2、3）异质结在界面处均形成了电势差，在其内部形成了从g-C₃N₄层指向GaN层的内置电场。GaN/g-C₃N₄-V_1N异质结的界面电势差值最大且红移现象最为明显，表明GaN/g-C₃N₄-V_1N异质结相较其他2个N缺陷异质结光学性能最好。氮缺陷的引入在不同程度上提高了GaN/g-C₃N₄异质结在红外光区域的光吸收能力。

First principles study of the effect of nitrogen defects on the electronic structure and optical property of GaN/g-C3N4 heterojunction

The stability, electronic structure, work function, and optical properties of monolayer GaN, g-C₃N₄, GaN/g-C₃N₄ heterojunctions and three nitrogen-deficient GaN/g-C₃N₄-V_XN (X=1, 2, 3) heterojunctions were investigated based on the first-principles plane wave super-soft pseudopotential method under density generalized theory. The calculated results show that the lattice mismatch rate of the GaN/g-C₃N₄ heterojunction is extremely low (0.8%) and is a complete co-lattice. Compared with monolayer g-C₃N₄, the conduction bands of the GaN/g-C₃N₄ and GaN/g-C₃N₄-V_XN (X=1, 2, 3) heterojunctions are shifted in the low-energy direction and the valence bands are shifted upward, which leads to the reduction of the band gap, and the density of states all show orbital hybridization. The GaN/g-C₃N₄ and GaN/g-C₃N₄-V_XN (X=1, 2, 3) heterojunctions all form a potential difference at the interface, forming the built-in electric fields from the g-C₃N₄ layer to the GaN layer. The GaN/g-C₃N₄-V_1N heterojunction has the largest interfacial potential difference and the most obvious red-shift phenomenon, indicating that the GaN/g-C₃N₄-V_1N heterojunction has the best optical performance compared to the other two N-defective heterojunctions. The introduction of nitrogen vacancies improves the light absorption ability of GaN/g-C₃N₄ heterojunction in the infrared region to different degrees.