Monolayer MoSe₂ grown by chemical vapor deposition for fast photodetection

Monolayer molybdenum disulfide (MoS₂) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the electrical and optoelectronic properties of monolayer MoS₂ devices. Here, highly crystalline molybdenum diselenide (MoSe₂) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS₂ and MoSe ₂ monolayers reveals that the MoSe₂ monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe₂ presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS₂ monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS₂. This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe₂ and MoS₂ and is useful for guiding future designs in 2D material-based optoelectronic devices.