Linardy Eric, Yadav Dinesh, Vella Daniele, Verzhbitskiy Ivan A, Watanabe Kenji, Taniguchi Takashi, Pauly Fabian, Trushin Maxim, Eda Goki
Department of Physics, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117551.
Centre for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, Singapore 117546.
Nano Lett. 2020 Mar 11;20(3):1647-1653. doi: 10.1021/acs.nanolett.9b04756. Epub 2020 Feb 26.
Strong many-body interactions in two-dimensional (2D) semiconductors give rise to efficient exciton-exciton annihilation (EEA). This process is expected to result in the generation of unbound high energy carriers. Here, we report an unconventional photoresponse of van der Waals heterostructure devices resulting from efficient EEA. Our heterostructures, which consist of monolayer transition metal dichalcogenide (TMD), hexagonal boron nitride (hBN), and few-layer graphene, exhibit photocurrent when photoexcited carriers possess sufficient energy to overcome the high energy barrier of hBN. Interestingly, we find that the device exhibits moderate photocurrent quantum efficiency even when the semiconducting TMD layer is excited at its ground exciton resonance despite the high exciton binding energy and large transport barrier. Using ab initio calculations, we show that EEA yields highly energetic electrons and holes with unevenly distributed energies depending on the scattering condition. Our findings highlight the dominant role of EEA in determining the photoresponse of 2D semiconductor optoelectronic devices.
二维（2D）半导体中的强多体相互作用会引发高效的激子 - 激子湮灭（EEA）。这一过程预计会导致产生未束缚的高能载流子。在此，我们报道了由高效EEA引起的范德华异质结构器件的非常规光响应。我们的异质结构由单层过渡金属二硫属化物（TMD）、六方氮化硼（hBN）和少层石墨烯组成，当光激发载流子具有足够能量以克服hBN的高能势垒时，会表现出光电流。有趣的是，我们发现即使半导体TMD层在其基态激子共振处被激发，尽管激子结合能高且传输势垒大，该器件仍表现出适度的光电流量子效率。通过从头算计算，我们表明EEA会产生能量分布不均匀的高能电子和空穴，这取决于散射条件。我们的研究结果突出了EEA在决定二维半导体光电器件光响应方面的主导作用。
