Gate‐Tunable Photoresponse Time in Black Phosphorus–MoS₂ Heterojunctions

Abstract 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.