Excitonic Rydberg States in a Trilayer to Monolayer H 2 -Aided CVD-Grown Large-Area MoS 2 Film with Excellent UV to Visible Broad Band Photodetection Applications.

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.