Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA.
Nano Lett. 2013 Jun 12;13(6):2831-6. doi: 10.1021/nl4011172. Epub 2013 May 1.
In the monolayer limit, transition metal dichalcogenides become direct-bandgap, light-emitting semiconductors. The quantum yield of light emission is low and extremely sensitive to the substrate used, while the underlying physics remains elusive. In this work, we report over 100 times modulation of light emission efficiency of these two-dimensional semiconductors by physical adsorption of O2 and/or H2O molecules, while inert gases do not cause such effect. The O2 and/or H2O pressure acts quantitatively as an instantaneously reversible "molecular gating" force, providing orders of magnitude broader control of carrier density and light emission than conventional electric field gating. Physi-sorbed O2 and/or H2O molecules electronically deplete n-type materials such as MoS2 and MoSe2, which weakens electrostatic screening that would otherwise destabilize excitons, leading to the drastic enhancement in photoluminescence. In p-type materials such as WSe2, the molecular physisorption results in the opposite effect. Unique and universal in two-dimensional semiconductors, the effect offers a new mechanism for modulating electronic interactions and implementing optical devices.
在单层极限下，过渡金属二卤化物成为直接带隙、发光半导体。发光的量子产率低，对所使用的衬底极其敏感，而潜在的物理机制仍难以捉摸。在这项工作中，我们报告了通过 O2 和/或 H2O 分子的物理吸附，对这两种二维半导体的发光效率进行了 100 多倍的调制，而惰性气体不会产生这种效果。O2 和/或 H2O 压力定量地充当即时可逆的“分子门控”力，提供比传统电场门控更广泛的载流子密度和光发射控制幅度。物理吸附的 O2 和/或 H2O 分子会使 n 型材料（如 MoS2 和 MoSe2）电子耗尽，这削弱了静电屏蔽，否则会使激子失稳，从而导致光致发光的急剧增强。在 p 型材料（如 WSe2）中，分子物理吸附会产生相反的效果。这种效应在二维半导体中具有独特和普遍的性质，为调节电子相互作用和实现光学器件提供了一种新的机制。
