Field-confined BP/MLG heterojunctions for room-temperature MWIR photodetectors

We report a simulation-driven black phosphorus (BP)/multilayer graphene (MLG) heterojunction concept for room-temperature mid-wave infrared (MWIR, 3–5 μm) photodetection. BP is selected as the active semiconductor because its thickness-dependent direct bandgap can align with MWIR photon energies, while MLG provides a highly conductive, van der Waals-compatible contact layer that can mitigate limitations commonly encountered at metal/2D interfaces. The proposed vertical p+–i–p–n+ stack uses doped BP to shape the electrostatic potential and confine a strong internal field within the intrinsic BP region, enabling efficient carrier separation and high-field transport under bias. The computed current–voltage characteristics show a clear transition into a high-field operating regime, and the responsivity exhibits a pronounced spectral maximum near 3.4 μm. At the onset condition, the responsivity reaches R = 13.15 AW−1 and the EQE attains 115–141.5% in the 3.2–3.46 μm band at 300 K. These results position BP/MLG heterojunctions as a practical 2D-material platform for compact, cooling-free MWIR photodetectors and motivate experimental realization using controlled BP doping and scalable van der Waals contacts.