Excitonic Rydberg States in a Trilayer to Monolayer H₂-Aided CVD-Grown Large-Area MoS₂ Film with Excellent UV to Visible Broad Band Photodetection Applications

Abstract

The diverse nature of optoelectronic properties of few-layer or monolayer MoS 2 is generally dominated by A and B excitons. Occasionally, strong Coulombic interactions within the 2D monolayer led to the creation of hydrogen-like Rydberg states of excitons in MoS 2 similar to other 2D monolayers. In this paper, a simple process is used to convert trilayer MoS 2 films to a monolayer by introducing H 2 gas during chemical vapor deposition. Remarkably, alongside the usual A, B excitons, and A − trion, the appearance of the Rydberg states is evidenced by photoluminescence spectra even at room temperature; also, there is an increase in their areal percentage with an increase in H 2 content. The s-type excited Rydberg states up to the fourth order (n = 5) and third order (n = 4) of A and B excitons, respectively, have been probed from the photoluminescence spectra at 93 K. Unprecedentedly, the first-order derivative of room-temperature photocurrent spectrum reveals the Rydberg states concurrently and elaboratively. Furthermore, the large-area MoS 2 films exhibit photoresponse in a broad UV to visible region with excellent photosensitivity (∼10 2 ) toward both UV and visible lights. Not only does this provide a profound understanding of the excitonic Rydberg states but also highlights the considerable potential of large-area monolayer MoS 2 overcoming the difficulty of tiny flake-related 2D device endeavors.

Manipulating Trion and Biexciton Emissions in Monolayer WS2 by Sandwiching with Ultrathin ZnO Layers for Excitonic Light Emission Applications

“…The inset displays the magnified spectrum in the 2.2–2.46 eV range. The low-intensity transitions may correspond to the s-type excited Rydberg states of the A exciton, while the broad background peak centered at around ∼2.41 eV corresponds to the ground state B exciton of 1L-WS 2 . , …”