Light Absorption and Emission Dominated by Trions in the Type-I van der Waals Heterostructures
Light Absorption and Emission Dominated by Trions in the Type-I van der Waals Heterostructures
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DOI：
10.1021/acsphotonics.0c01942
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发表时间：
2021-06-11
期刊：
影响因子：
7
通讯作者：
Choi, Hyunyong
中科院分区：
文献类型：
--
作者：
Bae, Hyemin;Kim, Suk Hyun;Choi, Hyunyong
范德华异质结构（vdW）为控制原子薄二维材料的能带排列提供了一种强有力的方法。在光照下，光学响应主要由库仑束缚的电子-空穴准粒子主导，如激子、三角子和双激子，它们的贡献取决于异质结构的类型。对于ii型异质结构，已经确定光激发导致电子和空穴在不同层中分离，并且辐射复合以层间激子为主。相反，对于i型情况下对应的光学响应知之甚少。了解i型异质结构的光学特性对于全面探索二维异质堆的准粒子物理特性具有重要意义。在这项研究中，我们对由单层MoTe2和WSe2组成的i型vdW异质堆进行了光谱学研究。光致发光和反射对比光谱分析表明，该材料的光吸收和发射主要由库仑束缚的三极管控制。重要的是，我们观察到，与共振光激发下的激子发射相比，在WSe2/MoTe2/WSe2异质三层中，MoTe2的trion发射变得更强。对光致发光激发的详细研究进一步揭示了电荷转移机制可能是我们观察到的原因，这与ii型结构中激子主导的偶极子-偶极子能量转移不同。我们的演示表明，i型vdW异质堆叠为通过多体库仑束缚态设计光物质相互作用提供了新的机会。
van der Waals (vdW) heterostructures provide a powerful method to control the alignment of energy bands of atomically thin 2D materials. Under light illumination, the optical responses are dominated by Coulomb-bound electron-hole quasiparticles, for example, excitons, trions, and biexcitons, whose contributions accordingly depend on the types of heterostructures. For type-II heterostructures, it has been well established that light excitation results in electrons and holes that are separated in different layers, and the radiative recombination is dominated by the interlayer excitons. On the contrary, little is known about the corresponding optical responses of type-I cases. Understanding the optical characteristics of type-I heterostructures is important to the full exploration of the quasiparticle physics of the 2D heterostacks. In this study, we performed optical spectroscopy on type-I vdW heterostacks composed of monolayer MoTe2 and WSe2. Photoluminescence and reflection contrast spectroscopy show that the light absorption and emission are dominated by the Coulomb-bound trions. Importantly, we observed that the MoTe2 trion emission gets stronger compared with the exciton emission under resonant light excitation to the WSe2 trion absorption state, especially in the WSe2/MoTe2/WSe2 heterotrilayer. A detailed study of photoluminescence excitation further reveals that the charge-transfer mechanism is likely responsible for our observation, which differs from the exciton-dominated dipole-dipole energy transfer in type-II structures. Our demonstration implies that the type-I vdW heterostack provides new opportunities to engineer the light-matter interactions through many-body Coulomb-bound states.