Air-Stable Room-Temperature Mid-Infrared Photodetectors Based on hBN/Black Arsenic Phosphorus/hBN Heterostructures*

Recently, layered black phosphorus (BP) has been explored intensively for infrared optoelectronic applications due to its high carrier mobility and the moderate direct bandgap (about 0.33 electron volt) in the thin film form. In this work, we demonstrate mid-infrared photodetectors based on black arsenic phosphorus (b-As_xP_1-x), whose bandgap can be below 0.15 electron volt by the introduction of arsenic. Mid-infrared photodetectors have been demonstrated leveraging the hexagonal boron nitride (hBN)/b-As_0.83P_0.17/hBN heterostructures. The encapsulation of hBN prevents b-As_0.83P_0.17 from oxidization and eliminates surface trap states, therefore the as-fabricated photodetectors work in intrinsic photoconductive mode, and show peak room-temperature extrinsic responsivity of 320, 24.7, and 1.03 mA/W at 3.4, 5.0, and 7.7 μm, respectively. The broadband and high-speed detection at mid-infrared illustrates the potential of b-As_0.83P_0.17 for optoelectronic applications, such as thermal imaging, biomedical sensing, and free-space mid-infrared communications.