通过邻近金属板提高2D半导体中的量子产率
Boosting quantum yields in 2D semiconductors via proximal metal plates
摘要：
单层过渡金属二硫属化物（1L-TMD）作为原子级薄的直接带隙半导体具有巨大的潜力，可以用作量子光子器件的方便构建块。然而，由于TMD中的缺陷陷阱和强激子-激子相互作用而导致的激子寿命短，显著限制了这类材料的激子发射效率。在这里，我们表明，激子-激子偶极场相互作用在1L-WS2可以有效地使用超平的金膜衬底分离的多层六方氮化硼进行筛选。在这种几何结构下，由于在金属内部形成有效的镜像偶极子，偶极激子-激子相互作用变为四极-四极相互作用。抑制激子-激子相互作用导致量子产率显著提高一个数量级，这也伴随着激子-激子湮灭（EEA）速率的降低，如通过时间分辨光学测量所证实的。一个半经典模型占屏蔽的偶极-偶极相互作用定性捕获EEA对激子密度的依赖。我们的研究结果表明，TMD中的基本EEA过程可以通过近端金属屏蔽来设计，这代表了一种实现高效2D光发射器的实用方法。
英文摘要：
Monolayer transition metal dichalcogenides (1L-TMDs) have tremendous potential as atomically thin, direct bandgap semiconductors that can be used as convenient building blocks for quantum photonic devices. However, the short exciton lifetime due to the defect traps and the strong exciton-exciton interaction in TMDs has significantly limited the efficiency of exciton emission from this class of materials. Here, we show that exciton-exciton dipolar field interaction in 1L-WS2 can be effectively screened using an ultra-flat Au film substrate separated by multilayers of hexagonal boron nitride. Under this geometry, dipolar exciton-exciton interaction becomes quadrupole-quadrupole interaction because of effective image dipoles formed inside the metal. The suppressed exciton-exciton interaction leads to a significantly improved quantum yield by an order of magnitude, which is also accompanied by a reduction in the exciton-exciton annihilation (EEA) rate, as confirmed by time-resolved optical measurements. A semiclassical model accounting for the screening of the dipole-dipole interaction qualitatively captures the dependence of EEA on exciton densities. Our results suggest that fundamental EEA processes in the TMD can be engineered through proximal metallic screening, which represents a practical approach towards high-efficiency 2D light emitters.
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