Exciton physics and device application of two-dimensional transition metal dichalcogenide semiconductors

Abstract

Two-dimensional group-VI transition metal dichalcogenide semiconductors, such as MoS2, WSe2 and others, exhibit strong light-matter coupling and possess direct band gaps in the infrared and visible spectral regimes, making them potentially interesting candidates for various applications in optics and optoelectronics. Here, we review their optical and optoelectronic properties with emphasis on exciton physics and devices. As excitons are tightly bound in these materials and dominate the optical response even at room-temperature, their properties are examined in depth in the first part of this article.We discuss the remarkably versatile excitonic landscape, including bright, dark, localized and interlayer excitons. In the second part, we provide an overview on the progress in optoelectronic device applications, such as electrically driven light emitters, photovoltaic solar cells, photodetectors and opto-valleytronic devices, again bearing in mind the prominent role of excitonic effects. We conclude with a brief discussion on challenges that remain to be addressed to exploit the full potential of transition metal dichalcogenide semiconductors in possible exciton-based applications.

Emerging Applications of Elemental 2D Materials

“…[4][5][6][7] This interest has been generated by the discovery of new and exciting physics such as nontrivial topology, [8][9][10] high-temperature ballistic transport, [11,12] valleytronics, [13] and other optoelectronic [14] properties that arise predominantly due to their 2D nature; these have recently been discussed in a number of excellent reviews. [6,[14][15][16] As a result, atomically thin materials are being targeted for a number of potential next-generation technology relevant applications, such as spintronics, advanced nanoelectronics, nanosensing, and many more. Among layered 2D materials, research interest in elemental materials has rejuvenated over the past few years, driven largely by the search for atomically thin materials beyond graphene that exhibit unique and exciting properties.…”

Multiphonon Raman Scattering in Transition Metal Dichalcogenide Double Layers

“…Varieties of double layers and Van der Waals heterostructures by vertically stacking different monolayer transition metal chalcogenides (TMDs) provide an attractive platform for studying the effects of light–matter interaction . An increasing number of experiments have proved that strong interlayer excitons are formed with valley‐contrasting selection properties in these structures and play a predominate role in determining various appealing optical properties, such as anomalous light cones are locked to the direction of exciton velocity, optical‐induced exciton spin Hall effect, and partial light–matter polarized eigenstates due to strong exciton–photon coupling, which promise exciting opportunities for next‐generation electronic and optoelectronic devices with valley functionalities …”

“…Many experiments have proved that binding energies of interlayer excitons are in the range of several hundreds of meV and much more larger than in the traditional coupled double quantum well systems. This means that these excitons are very stable even at room temperatures, which offer the opportunity to study room‐temperature optical properties and the potential excitonic devices . Another property is that electrons and holes are spatially separated in different layers, which gives rise to the drastic reduction of the overlap between the electron and hole wavefunctions and thus their lifetimes are orders of magnitude longer than intralayer excitons in monolayer TMDs .…”

“…[1][2][3][4][5] An increasing number of experiments [5][6][7] have proved that strong interlayer excitons are formed with valley-contrasting selection properties in these structures and play a predominate role in determining various appealing optical properties, such as anomalous light cones are locked to the direction of exciton velocity, [8] opticalinduced exciton spin Hall effect, [9] and partial light-matter polarized eigenstates due to strong exciton-photon coupling, [10] which promise exciting opportunities for next-generation electronic and optoelectronic devices with valley functionalities. [11,12] These unique phenomena as aforementioned mainly stem from two remarkable properties of interlayer excitons. One is the exceptional large binding energy.…”

“…This means that these excitons are very stable even at room temperatures, which offer the opportunity to study room-temperature optical properties and the potential excitonic devices. [12,16] Another property is that electrons and holes are spatially separated in different layers, which gives rise to the drastic reduction of the overlap between the electron and hole wavefunctions and thus their lifetimes are orders of magnitude longer than intralayer excitons in monolayer TMDs. [17][18][19] This property holds the potential applications for creating excitonic signal processing devices and excitonic circuits with sufficient lifetime.…”