Direct vapor phase growth process and robust photoluminescence properties of large area MoS^sub 2^ layers

There has been growing research interest in the use of molybdenum disulfide in the fields of optoelectronics and energy harvesting devices, by virtue of its indirect-to-direct band gap tunability. However, obtaining large area thin films of MoS^sub 2^ for future device applications still remains a challenge. In the present study, the amounts of the precursors (S and MoO3) were varied systematically in order to optimize the growth of highly crystalline and large area MoS^sub 2^ layers by the chemical vapor deposition method. Careful control of the amounts of precursors was found to the key factor in the synthesis of large area highly crystalline flakes. The thickness of the layers was confirmed by Raman spectroscopy and atomic force microscopy. The optical properties and chemical composition were studied by photoluminescence (PL) and X-ray photoelectron spectroscopy. The emergence of strong direct excitonic emissions at 1.82 eV (A-exciton, with a normalized PL intensity of 55 × 10^sup 3^) and 1.98 eV (B-exciton, with a normalized PL intensity of 5 × 10^sup 3^) of the sample at room temperature clearly indicates the high luminescence quantum efficiency. The mobility of the films was found to be 0.09 cm^sup 2^/(V·s) at room temperature. This study provides a method for the controlled synthesis of high-quality two-dimensional (2D) transition metal dichalcogenide materials, useful for applications in nanodevices, optoelectronics and solar energy conversion. [Figure not available: see fulltext.][PUBLICATION ABSTRACT]