Remarkable quality improvement of as-grown monolayer MoS2 by sulfur vapor pretreatment of SiO2/Si substrates

Abstract

Monolayer MoS₂ is a direct bandgap semiconductor which is believed to be one of the most promising candidates for optoelectronic devices. Chemical vapor deposition (CVD) is the most popular method to synthesize monolayer MoS₂ with a large area. However, many defects are always found in monolayer MoS₂ grown by CVD, such as sulfur vacancies, which severely degrade the performance of devices. This work demonstrates a concise and effective method for direct growth of high quality monolayer MoS₂ by using SiO₂/Si substrates pretreated with sulfur vapor. The MoS₂ monolayer obtained using this method shows about 20 times PL intensity enhancement and a much narrower PL peak width than that grown on untreated substrates. Detailed characterization studies reveal that MoS₂ grown on sulfur vapor pretreated SiO₂/Si substrates has a much lower density of sulfur vacancies. The synthesis of monolayer MoS₂ with high optical quality and low defect concentration is critical for both fundamental physics studies and potential practical device applications in the atomically thin limit.