Self-powered, flexible near-infrared photodetector with high responsivity and strain robustness via stacking-engineered interfacial polarization of a BAs homobilayer

Two-dimensional photodetectors have become the preferred choice for future photodetectors with their advantages of being lightweight, portable, and high performance. However, the intrinsic properties of two-dimensional semiconductors make them susceptible to external disturbances, rendering them unsuitable for complex usage scenarios. Additionally, the power supply issue of small-scale devices relies on traditional van der Waals heterostructures with type-II band alignment for self-powering. Nonetheless, lattice and momentum mismatch issues for heterostructures have consistently hindered design efforts. Through first-principle calculations and quantum transport simulations, we introduce a groundbreaking self-powered near-infrared (NIR) photodetector based on 2D homobilayer BAs, achieved through tailored stacking techniques that induce spontaneous electrical polarization. The resulting ab-stacked BAs/BAs vdW homostructure forms a robust p-n homojunction endowed with a potent built-in polarization electric field, courtesy of the inherent spontaneous polarization along the out-of-plane direction. Leveraging broad momentum-space compatibility, high carrier mobility, and robust NIR light absorption, our 2D homobilayer BAs photodetector exhibits a wide NIR response range (780 nm--1600 nm) and an impressive responsivity of 122 mA/W even at zero bias. Under varying strains, homostructures of bilayer BAs exhibit remarkable robustness, maintaining a direct band gap and type-II band alignment across the entire strain spectrum. Moreover, under compressive strain, notable enhancements are observed in optical absorption coefficient and responsivity. Notably, the polarization induced by the ab-stacked interface is tunable, with polarization intensity increasing with the number of interfaces, presenting a straightforward method to amplify system polarization. Our study delineates a viable strategy for developing high-performance self-powered NIR photodetectors through strategic stacking engineering.