Moody Galan, Schaibley John, Xu Xiaodong
National Institute of Standards & Technology, 325 Broadway, Boulder, CO 80305.
Department of Physics, University of Washington, Seattle, Washington 98195.
J Opt Soc Am B. 2016 Jul 1;33(7):C39-C49. doi: 10.1364/JOSAB.33.000C39. Epub 2016 Apr 19.
Since the discovery of semiconducting monolayer transition metal dichalcogenides, a variety of experimental and theoretical studies have been carried out seeking to understand the intrinsic exciton population recombination and valley relaxation dynamics. Reports of the exciton decay time range from hundreds of femtoseconds to ten nanoseconds, while the valley depolarization time can exceed one nanosecond. At present, however, a consensus on the microscopic mechanisms governing exciton radiative and non-radiative recombination is lacking. The strong exciton oscillator strength resulting in up to ~ 20% absorption for a single monolayer points to ultrafast radiative recombination. However, the low quantum yield and large variance in the reported lifetimes suggest that non-radiative Auger-type processes obscure the intrinsic exciton radiative lifetime. In either case, the electron-hole exchange interaction plays an important role in the exciton spin and valley dynamics. In this article, we review the experiments and theory that have led to these conclusions and comment on future experiments that could complement our current understanding.
自从发现半导体单层过渡金属二硫属化物以来，人们进行了各种实验和理论研究，试图了解本征激子群体复合和谷弛豫动力学。关于激子衰减时间的报道范围从几百飞秒到十纳秒，而谷去极化时间可能超过一纳秒。然而，目前对于控制激子辐射和非辐射复合的微观机制尚未达成共识。强激子振子强度导致单层的吸收高达约20%，这表明存在超快辐射复合。然而，低量子产率和报道寿命的巨大差异表明，非辐射俄歇型过程掩盖了本征激子辐射寿命。在这两种情况下，电子 - 空穴交换相互作用在激子自旋和谷动力学中都起着重要作用。在本文中，我们回顾了导致这些结论的实验和理论，并对可能补充我们当前理解的未来实验进行了评论。
