Black Phosphorus Infrared Photodetectors with Fast Response and High Photoresponsivity

Recently, black phosphorus (BP) has attracted enormous attention as the potential materials for next‐generation photonic device applications due to the high carrier mobility and the narrow bandgap. However, the metal–semiconductor–metal (MSM) structure of BP photodetectors cannot achieve simultaneously high photoresponsivity and fast photoresponse, due to its natural surface defects, the thinness of absorption layer, and the instability of BP in the air, which limits the application of BP MSM structure photodetectors. Here, infrared photodetectors with the multilayer BP sandwiched between the top protective layer of boron nitride and the bottom Au electrodes are demonstrated. The BP photodetectors exhibit a fast photoresponse of ≈16 µs, a broadband photodetection up to ≈2 µm, a high light on/off ratio of ≈10 3 which is higher than most BP photodetectors, together with an acceptable photoresponsivity of ≈1.55 A W −1 for the wavelength of 1550 nm at room temperature. Scanning photocurrent microscopy measurements show that the mechanism of BP photodetectors is a combination of photovoltaic effect and photoconductive effect. This work demonstrates an effective way to design high‐performance photovoltaic/photoconductive devices based on 2D materials.