Near-Unity Light Absorption in a Monolayer WS₂ Van der Waals Heterostructure Cavity

Abstract

Excitons in monolayer transition-metal-dichalcogenides (TMDs) dominate their optical response and exhibit strong light-matter interactions with lifetime-limited emission. While various approaches have been applied to enhance light-exciton interactions inTMDs, the achieved strength have been far below unity, and a complete picture of its underlying physical mechanisms and fundamental limits has not been provided. Here, we introduce a TMD-based van der Waals heterostructure cavity that provides nearunity excitonic absorption, and emission of excitonic complexes that are observed at ultra-low excitation powers. Our results are in full agreement with a quantum theoretical framework introduced to describe the light-exciton-cavity interaction. We find that the subtle interplay between the radiative, non-radiative and dephasing decay rates plays a crucial role, and unveil a universal absorption law for excitons in 2D systems. This enhanced light-exciton interaction provides a platform for studying excitonic phase-transitions and quantum nonlinearities and enables new possibilities for 2D semiconductor-based optoelectronic devices. * These authors contributed equally †

Guide to optical spectroscopy of layered semiconductors

“…In this process, the particular energy of the excitonic resonance of the layered semiconductor should be taken into account 88 . Recent results in TMD materials placed in front of mirrors show a modulation in the absorption strength of up to 100% due to interference/cavity effects [25][26][27][28] . The strong influence of the dielectric environment on the light-matter interaction of atomically thin semiconducting membranes motivates potential sensing applications, including new device architectures with precisely tunable optical properties.…”

“…New device concepts are based on physical properties emerging in the 2D limit. Examples that motivate optical spectroscopy work in this field are the electron valley index for information storage [20][21][22] , periodic quantum emitters in flexible membranes 23,24 , tunable absorption up to 100% by a single monolayer [25][26][27][28] or electrically switchable 2D magnetism 29 .…”

Tuning absorption and emission in monolayer semiconductors: a brief survey

“…Remarkably, the absorbance A = 1−|r tot | 2 can reach 100% under the condition that the reflectivity vanishes. The latter situation can be realized at ML encapsulated in hBN and deposited on a gold mirror (adapted from [47]). The peak absorption is maximal at 110 K when both radiative and non-radiative linewidths are equal.…”

“…The peak absorption is maximal when both radiative Γ rad and non-radiative Γ sca linewidths are equal. (a) Reprinted with permission from [47]. Copyright 2020 American Chemical Society.…”

“…Figure 4. (a) Temperature dependence of the absorption of the neutral exciton in a WS 2 ML encapsulated in hBN and deposited on a gold mirror (adapted from[47]). The peak absorption is maximal at 110 K when both radiative and non-radiative linewidths are equal.…”