Centimeter-Scale Synthesis of Monolayer WS<sub>2</sub> Using Single-Zone Atmospheric-Pressure Chemical Vapor Deposition: A Detailed Study of Parametric Dependence, Growth Mechanism, and Photodetector Properties
Pallavi Aggarwal, Shuchi Kaushik, Prashant Bisht, Madan Sharma, Aditya Singh, B. R. Mehta, Rajendra Singh
Abstract
Two-dimensional transition metal dichalcogenides offer exciting opportunities to tailor their electrical and optoelectronic properties, which provide them with a multitude of applications, following which their large-area synthesis holds high significance. Herein, we demonstrate NaCl-assisted centimeter-scale (1.5 × 1 cm2) growth of monolayer WS2 using an atmospheric-pressure chemical vapor deposition technique. We attempt to explicate the growth mechanism with the Volmer–Weber, Stranski–Krastanov, and Frank–van der Merwe modes by incorporating the importance of NaCl as a growth promoter and other parameters like the quantity of sulfur, temperature, gas flow rate, and hold time. The parameters optimized for large-area monolayer growth were found at a NaCl to WO3 w/w ratio of 1:2 and a sulfur to WO3 w/w ratio of 3:1, with a 1 min hold time at 820 °C in a 120 sccm argon gas flow. The optical microscope images along with the corresponding Raman and photoluminescence spectra were employed to examine the growth of the WS2 film at different sets of synthesis parameters. The photodetector fabricated on the as-grown film showed a high responsivity and specific detectivity of 4.27 mA/W and 1.27 × 1010 Jones, respectively, in the visible region and 261 mA/W and 7.72 × 1011 Jones, respectively, in the ultraviolet (UV) region. These results support its application in UV–visible photodetection.