Electrostatically Induced Black Phosphorus Infrared Photodiodes

Abstract Homojunctions are key elements in many mainstream electronic devices. However, conventional dopant‐based “pn” homojunctions are not easily achievable in new material families, such as the 2D materials. Several recent 2D material studies have shown that lateral pn homojunctions can instead be electrostatically induced using back gates localized to either the source or drain contacts. Here, a hBN‐encapsulated black phosphorus dual‐gate device containing a lateral pn homojunction, whose orientation can be switched via application of back gate voltages, is demonstrated. Importantly, this study extends the state‐of‐the‐art for this architecture by characterizing the photoresponse under infrared (λ = 2.2 µm) illumination. It is shown that when biased to form a homojunction, the device exhibits the photovoltaic effect, resulting in a specific detectivity of 8.5 × 10 8 cm Hz 1/2 W −1 at 77 K under short‐circuit conditions, and an open circuit photovoltage up to 175 mV at 77 K. Further, it is shown that the device can be operated in photoconductive mode, allowing a high responsivity of 0.55 A W −1 . This device is thus highly reconfigurable as it can be switched between photovoltaic and photoconductive modes of operation to prioritize low noise and fast response or high responsivity.