Investigation of the Thermal Stability of MOCVD-Synthesized WS2 Monolayer Films

Abstract

High-temperature applications and fabrication processes require a complete understanding of the thermal stability of WS2 under different ambient conditions, such as air, argon, and forming gas. While reports exist on powder-source chemical vapor deposition (PS-CVD) growth of predominantly polycrystalline WS2, investigations into WS2 synthesized by metal–organic chemical vapor deposition (MOCVD), which better aligns with industrial wafer-scale deposition standards, remain scarce. Investigating the thermal stability of MOCVD-grown WS2 is particularly necessary, as the precursors and processing conditions determine the microstructure and subsequent properties. In this manuscript, we investigate the thermal stability of WS2 synthesized by MOCVD in air, argon, and forming gas at elevated temperatures to determine the safe window of processing and operating parameters. Scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy confirm the evolution of the morphological, chemical, and optical properties of the films. This study reveals that the WS2 films degrade in air at 400 °C after 15 min, while retaining their pristine properties in argon and forming gas at 500 °C after 15 min. While Raman spectroscopy can readily detect complete removal of WS2 films, XPS and PL spectra are more sensitive to oxidation and defect creation in WS2 films. A complete correlation of morphological, optical, and chemical characterizations has been provided to estimate the thermal stability of the films in different environments.