Yu Yiling, Yu Yifei, Li Guoqing, Puretzky Alexander A, Geohegan David B, Cao Linyou
Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695, USA.
Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Sci Adv. 2020 Dec 18;6(51). doi: 10.1126/sciadv.abb4823. Print 2020 Dec.
Two-dimensional (2D) semiconductors bear great promise for application in optoelectronic devices, but the low diffusivity of excitons stands as a notable challenge for device development. Here, we demonstrate that the diffusivity of excitons in monolayer MoS can be improved from 1.5 ± 0.5 to 22.5 ± 2.5 square centimeters per second with the presence of trapped charges. This is manifested by a spatial expansion of photoluminescence when the incident power reaches a threshold value to enable the onset of exciton Mott transition. The trapped charges are estimated to be in a scale of 10 per square centimeter and do not affect the emission features and recombination dynamics of the excitons. The result indicates that trapped charges provide an attractive strategy to screen exciton scattering with phonons and impurities/defects. Pointing towards a new pathway to control exciton transport and many-body interactions in 2D semiconductors.
二维（2D）半导体在光电器件应用方面极具潜力，但激子的低扩散率是器件开发面临的一个显著挑战。在此，我们证明，在存在捕获电荷的情况下，单层MoS中激子的扩散率可从每秒1.5±0.5平方厘米提高到22.5±2.5平方厘米。当入射功率达到阈值以引发激子莫特转变时，这表现为光致发光的空间扩展。估计捕获电荷的密度为每平方厘米10个，且不影响激子的发射特性和复合动力学。该结果表明，捕获电荷为筛选激子与声子及杂质/缺陷的散射提供了一种有吸引力的策略。这为控制二维半导体中的激子输运和多体相互作用指明了一条新途径。
