Gate‐Tunable Photoresponse Time in Black Phosphorus–MoS2 Heterojunctions

Gate‐/wavelength‐dependent scanning photocurrent measurements of black phosphorous (BP)–MoS2 heterojunctions have shown that the Schottky barrier at the MoS2–metal interface plays an important role in the photoresponse dynamics of the heterojunction. When the Fermi level is close to the conduction band of MoS2, photoexcited carriers can tunnel through the narrow depletion region at the MoS2–metal interface, leading to a short response time of 13 µs regardless of the incident laser wavelength. This response speed is comparable or better than that of other few‐layer BP–MoS2 heterojunctions. Conversely, when the MoS2 channel is in the off‐state, the resulting sizeable Schottky barrier and depletion width make it difficult for photoexcited carriers to overcome the barrier. This significantly delays the carrier transit time and thus the photoresponse speed, leading to a wavelength‐dependent response time since the photoexcited carriers induced by short wavelength photons have a higher probability to overcome the Schottky barrier at the MoS2–metal interface than long wavelength photons. These studies not only shed light on the fundamental understanding of photoresponse dynamics in BP–MoS2 heterojunctions, but also open new avenues for engineering the interfaces between 2D materials and metal contacts to reduce the response time of 2D optoelectronics. Wavelength‐ and gate‐dependent photoresponse speed is demonstrated in black phosphorus (BP)–MoS2 heterojunctions. Through modulating the Schottky barrier at the MoS2–metal interface with an applied gate voltage photoexcited carriers are either able to easily tunnel through or unable to overcome this barrier, shedding light on the significance of this barrier in the photoresponse dynamics of 2D materials.