Point Defects and Localized Excitons in 2D WSe2,ACS Nano

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Point Defects and Localized Excitons in 2D WSe2
ACS Nano ( IF 15.8 ) Pub Date : 2019-05-10 00:00:00 , DOI: 10.1021/acsnano.9b02316
Yu Jie Zheng _{1,

2} , Yifeng Chen ₂ , Yu Li Huang _{1,

3} , Pranjal Kumar Gogoi ₁ , Ming-Yang Li ₄ , Lain-Jong Li ₄ , Paolo E. Trevisanutto ₂ , Qixing Wang ₁ , Stephen J. Pennycook ₅ , Andrew T. S. Wee _{1,

2} , Su Ying Quek _{1,

2}

Affiliation

Identifying the point defects in 2D materials is important for many applications. Recent studies have proposed that W vacancies are the predominant point defect in 2D WSe₂, in contrast to theoretical studies, which predict that chalcogen vacancies are the most likely intrinsic point defects in transition metal dichalcogenide semiconductors. We show using first-principles calculations, scanning tunneling microscopy (STM), and scanning transmission electron microscopy experiments that W vacancies are not present in our CVD-grown 2D WSe₂. We predict that O-passivated Se vacancies (O_Se) and O interstitials (O_ins) are present in 2D WSe₂, because of facile O₂ dissociation at Se vacancies or due to the presence of WO₃ precursors in CVD growth. These defects give STM images in good agreement with experiment. The optical properties of point defects in 2D WSe₂ are important because single-photon emission (SPE) from 2D WSe₂ has been observed experimentally. While strain gradients funnel the exciton in real space, point defects are necessary for the localization of the exciton at length scales that enable photons to be emitted one at a time. Using state-of-the-art GW-Bethe-Salpeter-equation calculations, we predict that only O_ins defects give localized excitons within the energy range of SPE in previous experiments, making them a likely source of previously observed SPE. No other point defects (O_Se, Se vacancies, W vacancies, and Se_W antisites) give localized excitons in the same energy range. Our predictions suggest ways to realize SPE in related 2D materials and point experimentalists toward other energy ranges for SPE in 2D WSe₂.

中文翻译：

2D WSe _2中的点缺陷和局部激子

识别2D材料中的点缺陷对于许多应用而言很重要。与理论研究相反，最近的研究提出W空位是2D WSe ₂中的主要点缺陷，理论研究预测，硫属元素空位是过渡金属二卤化半导体中最可能的固有点缺陷。我们使用第一原理计算，扫描隧道显微镜（STM）和扫描透射电子显微镜实验表明，在我们的CVD生长的2D WSe ₂中不存在W空位。我们预测O钝化的Se空位（O _Se）和O间隙（O _ins）存在于2D WSe _2中，因为O ₂较容易在Se空位处解离或由于CVD生长中存在WO ₃前体。这些缺陷使STM图像与实验良好吻合。2D WSe ₂中点缺陷的光学性质很重要，因为已经通过实验观察到了2D WSe _2的单光子发射（SPE）。尽管应变梯度使激子在实际空间中漏斗，但对于在长度尺度上使激子定位的点缺陷是必需的，该长度尺度使光子一次可以发射一次。使用最新的GW-Bethe-Salpeter方程计算，我们预测只有O _ins在先前的实验中，缺陷会在SPE的能量范围内产生局部激子，使其成为先前观察到的SPE的可能来源。没有其他点缺陷（O _Se，Se空位，W空位和Se _W反位点）在相同的能量范围内产生局部激子。我们的预测提出了在相关2D材料中实现SPE的方法，并将实验者指向2D WSe _2中SPE的其他能量范围。

更新日期：2019-05-10

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