Probing negatively charged and neutral excitons in MoS2/hBN and hBN/MoS2/hBN van der Waals heterostructures
Probing negatively charged and neutral excitons in MoS2/hBN and hBN/MoS2/hBN van der Waals heterostructures
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DOI：
10.1088/1361-6528/abd507
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发表时间：
2021-04-02
期刊：
影响因子：
3.5
通讯作者：
Bryja, L.
中科院分区：
文献类型：
--
作者：
Jadczak, J.;Kutrowska-Girzycka, J.;Bryja, L.
由六方氮化硼封装的单层过渡金属二硫属化物组装而成的高质量范德华异质结构能够观察微妙的光学和自旋谷特性，这些特性的识别超出了直接剥离在标准 SiO2/Si 基底上的结构的范围。在这里，我们描述了基于堆叠在不同厚度的六方氮化硼层和六方氮化硼封装的单层上的未封端的单层MoS2的不同范德华异质结构。根据掺杂水平，它们揭示了激子复合物的精细结构，即中性和带电激子。在没有 hBN 帽的特定 MoS2/hBN 异质结构的发射光谱中，我们解析了两个 trion 峰 T-1 和 T-2，能量分裂约为 10 meV，类似于钨基材料中的一对单线态和三线态 trion 峰（T-S 和 T-T）。这些三重子特征的存在表明，单层 MoS2 具有暗激子基态，尽管具有“明亮”的自旋极化导带单粒子排列。此外，我们还发现，有效激子 g 因子显着取决于电子浓度，并且六方氮化硼封装结构的有效激子 g 因子达到最低值 -2.47，这揭示了接近中性的掺杂状态。在无盖帽的 MoS2 结构中，激子 g 因子在 -1.15 至 -1.39 之间变化，具体取决于底部 hBN 层的厚度，并随着温度升高而降低。
High-quality van der Waals heterostructures assembled from hBN-encapsulated monolayer transition metal dichalcogenides enable observations of subtle optical and spin-valley properties whose identification was beyond the reach of structures exfoliated directly on standard SiO2/Si substrates. Here, we describe different van der Waals heterostructures based on uncapped single-layer MoS2 stacked onto hBN layers of different thicknesses and hBN-encapsulated monolayers. Depending on the doping level, they reveal the fine structure of excitonic complexes, i.e. neutral and charged excitons. In the emission spectra of a particular MoS2/hBN heterostructure without an hBN cap we resolve two trion peaks, T-1 and T-2, energetically split by about 10 meV, resembling the pair of singlet and triplet trion peaks (T-S and T-T) in tungsten-based materials. The existence of these trion features suggests that monolayer MoS2 has a dark excitonic ground state, despite having a 'bright' single-particle arrangement of spin-polarized conduction bands. In addition, we show that the effective excitonic g-factor significantly depends on the electron concentration and reaches the lowest value of -2.47 for hBN-encapsulated structures, which reveals a nearly neutral doping regime. In the uncapped MoS2 structures, the excitonic g-factor varies from -1.15 to -1.39 depending on the thickness of the bottom hBN layer and decreases as a function of rising temperature.