CVD synthesis of large-area, highly crystalline MoSe2 atomic layers on diverse substrates and application to photodetectors

Abstract

Synthesis of large-area, atomically thin transition metal dichalcogenides (TMDs) on diverse substrates is of central importance for the large-scale fabrication of flexible devices and heterojunction-based devices. In this work, we successfully synthesized a large area of highly-crystalline MoSe₂ atomic layers on SiO₂/Si, mica and Si substrates using a simple chemical vapour deposition (CVD) method at atmospheric pressure. Atomic force microscopy (AFM) and Raman spectroscopy reveal that the as-grown ultrathin MoSe₂ layers change from a single layer to a few layers. Photoluminescence (PL) spectroscopy demonstrates that while the multi-layer MoSe₂ shows weak emission peaks, the monolayer has a much stronger emission peak at ∼1.56 eV, indicating the transition from an indirect to a direct bandgap. Transmission electron microscopy (TEM) analysis confirms the single-crystallinity of MoSe₂ layers with a hexagonal structure. In addition, the photoresponse performance of photodetectors based on MoSe₂ monolayer was studied for the first time. The devices exhibit a rapid response of ∼60 ms and a good photoresponsivity of ∼13 mA/W (using a 532 nm laser at an intensity of 1 mW mm⁻² and a bias of 10 V), suggesting that MoSe₂ monolayer is a promising material for photodetection applications.