1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2].
1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2] Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Nat Mater. 2014 Dec;13(12):1091-5. doi: 10.1038/nmat4061. Epub 2014 Aug 31.
Two-dimensional (2D) transition metal dichalcogenides (TMDs) are emerging as a new platform for exploring 2D semiconductor physics. Reduced screening in two dimensions results in markedly enhanced electron-electron interactions, which have been predicted to generate giant bandgap renormalization and excitonic effects. Here we present a rigorous experimental observation of extraordinarily large exciton binding energy in a 2D semiconducting TMD. We determine the single-particle electronic bandgap of single-layer MoSe2 by means of scanning tunnelling spectroscopy (STS), as well as the two-particle exciton transition energy using photoluminescence (PL) spectroscopy. These yield an exciton binding energy of 0.55 eV for monolayer MoSe2 on graphene—orders of magnitude larger than what is seen in conventional 3D semiconductors and significantly higher than what we see for MoSe2 monolayers in more highly screening environments. This finding is corroborated by our ab initio GW and Bethe-Salpeter equation calculations which include electron correlation effects. The renormalized bandgap and large exciton binding observed here will have a profound impact on electronic and optoelectronic device technologies based on single-layer semiconducting TMDs.
二维（2D）过渡金属二卤族化合物（TMDs）正成为探索 2D 半导体物理的新平台。二维环境下的屏蔽作用减弱导致电子-电子相互作用显著增强，这预计会产生巨大的能带重整化和激子效应。在此，我们通过扫描隧道谱（STS）严格地观测到 2D 半导体 TMD 中具有非常大的激子束缚能。我们利用光致发光（PL）光谱确定了单层 MoSe2 的单粒子能带隙，以及双粒子激子跃迁能量。这表明在石墨烯上的单层 MoSe2 的激子束缚能为 0.55eV，比传统 3D 半导体中的激子束缚能大几个数量级，比我们在更高屏蔽环境中观察到的 MoSe2 单层激子束缚能大得多。我们的 GW 和 Bethe-Salpeter 方程的从头计算结果，其中包括电子相关效应，证实了这一发现。这里观察到的带隙重整化和大激子束缚将对基于单层半导体 TMD 的电子和光电设备技术产生深远的影响。
