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

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 in large area. However, many defects are always found in monolayer MoS2 grown by CVD, such as sulfur vacancies, which severely degrade the performance of device. This work demonstrates a concise and effective method about direct growth of high quality monolayer MoS2 by using SiO2/Si substrates treated by sulfur vapor in advance. MoS2 monolayer obtained by using this method shows about 20 times of PL intensity enhancement and much narrower PL peak width than that grown on untreated substrates. Detailed characterizations reveal that MoS2 grown on sulfur vapor pretreated SiO2/Si substrates has 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 study and potential practical device applications at atomically thin limit.