二维硒和碲的强体光伏效应和二次谐波产生
Strong bulk photovoltaic effect and second-harmonic generation in two-dimensional selenium and tellurium
摘要：
近年来，硒和碲的少层薄膜的制备为探索二维元素材料的新特性提供了一个新的平台。在这项工作中，我们已经进行了系统的第一性原理研究的电子，线性和非线性光学（NLO）性质的原子薄硒和碲薄膜的密度泛函理论与广义梯度近似加上剪刀修正使用的带隙从相对论混合Heyd-Scuseria-Ernzerhof功能计算。有趣的是，我们发现少层硒和碲具有大的二次谐波产生（SHG），线性电光效应，和体光伏效应。特别地，三层（TL）Te具有大的SHG系数，比广泛使用的NLO材料GAN的SHG系数大65倍以上。双层Te具有很大的静态二次谐波系数，是GAN的100倍以上。此外，单层（ML）Se具有大的SHG系数。此外，我们预测，TL Te具有很强的体光伏效应（BPVE），大于GeS，一个极性系统，迄今发现的最大的BPVE。虽然体和2D Se的移位电流电导率是可比的，但TL Te的移位电流电导率是体Te的移位电流电导率的五倍。最后，计算的电子能带结构的分析表明，2D Se和Te材料的强NLO响应主要来自于它们的低维结构，具有高各向异性，定向共价键，孤对电子，和相对较小的带隙。这些发现为寻找优良的NLO和BPVE材料提供了一种实用的策略。
英文摘要：
Few-layer selenium and tellurium films have been recently prepared, and they provide a new platform to explore novel properties of two-dimensional (2D) elemental materials. In this work, we have performed a systematic first-principles study on the electronic, linear, and nonlinear optical (NLO) properties of atomically thin selenium and tellurium films within the density-functional theory with the generalized gradient approximation plus scissors correction using the band gaps from the relativistic hybrid Heyd-Scuseria-Ernzerhof functional calculations. Interestingly, we find that few-layer Se and Te possess large second-harmonic generation (SHG), linear electro-optic effect, and bulk photovoltaic effect. In particular, trilayer (TL) Te possesses large SHG coefficient, being more than 65 times larger than that of GaN, a widely used NLO material. Bilayer (BL) Te has huge static SHG coefficient, being more than 100 times larger than that of GaN. Furthermore, monolayer (ML) Se possesses large SHG coefficient. Moreover, we predict that TL Te exhibits strong bulk photovoltaic effect (BPVE), being greater than that of GeS, a polar system with the largest BPVE found so far. Although the shift current conductivities of bulk and 2D Se are comparable, the shift current conductivities of TL Te are five times larger than those of bulk Te. Finally, an analysis of the calculated electronic band structures indicates that the strong NLO responses of 2D Se and Te materials are primarily derived from their low-dimensional structures with high anisotropy, directional covalent bonding, lone-pair electrons, and relatively small band gaps. These findings provide a practical strategy to search for excellent NLO and BPVE materials.
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