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半导体材料AAl^2C4（A=Zn，Cd，Hg；C=S，Se）的电子结构和光学性质
Electronic structures and optical properties of AAl2C4 （A = Zn, Cd, Hg; C S, Se） semiconductors＊
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摘要: 采用基于密度泛函理论的第一性原理方法，对具有缺陷型黄铜矿结构的半导体材料A^ⅡA12C^Ⅵ（A=Zn，Cd，Hg；C=S，Se）的构型和电子结构进行研究，并系统考察了各晶体的光学性质．对于线性光学性质，五种晶体在红外区和部分可见光区具有良好的透光性能，其中HgAl2S4和HgAl2Se4晶体具有适中的双折射率．在非线性光学性质方面，该类晶体倍频效应较强，理论预测得到的二阶静态倍频系数均较大（〉20pm／V）．体系的倍频效应主要来源于价带顶附近以S／Se价P轨道为主要成分的能带向含有较多A1／Hg价P成分的空带之间的跃迁．通过与已商业化的AgGaCz晶体光学性质的对比，结果表明HgAl2S4和HgAl2Se4是一类性能优良的红外非线性光学晶体材料．Abstract: First-principles density functional calculations are pertbrmed to study the geometries, the electronic anct me optical propemes or A^ⅡA12C^Ⅵ （A = Zn, Cd, Hg; C = S, Se） semiconductors each with a defect chalcopyrite structure. For the linear optical properties, five compounds show good transmissions of light in the IR and part of visible regions, and among them HgA12S4 and HgA12Se4 possess moderate birefringences. For the nonlinear optical properties, the strong second harmonic generation （SHG） response can be expected for these crystals, and the large static SHG coefficients （〉 20 pro/V） are predicted in this work. The SHG response of A^ⅡA12C4Ⅵsemiconductors can be attributed to the transitions from the bands near the top of valence band which are derived from S/Se p states to the unoccupied bands that are contributed by p states of A1 and Hg atoms. By comparing with the optical properties of the commercialized AgGaC2 crystals, our results indicate that HgA12S4 and HgA12Se4 compounds are good candidates for the second-order nonlinear optical crystals in the IR region.
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