Reconfigurable Symmetry-Broken van der Waals Ferroelectric Semiconductor Heterojunctions for All-in-One Optoelectronic Devices.

van der Waals heterojunctions (VHJs) consisting of distinct atomically thin semiconductors with weak interfacial interactions and complementary bandgaps provide a large degree of freedom to design their device structures for multifunctional applications. However, device multifunctionalities highly rely on heterojunctions with tunable band offsets and band alignment type. Herein, we theoretically explore a class of VHJs composed of two-dimensional low-symmetry semiconductors and ferroelectric (FE) semiconductors for achieving multifunctional device applications. Our results indicate that the switchable FE polarization and symmetry-breaking effect enable momentum-matching VHJs with tunable bandgap, band alignment type, and band offset values. Using an α-In2Se3/GeSe VHJ as a prototype example, we demonstrate a type-II-to-type-III band alignment transition driven by the FE polarization switching, resulting in a notable difference of carrier concentration and resistance state between the two FE states. The α-In2Se3/GeSe device presents a giant tunneling electroresistance ratio as high as 1015% that is at least 2 orders of magnitude larger than other VHJ devices. Benefiting from the momentum-matching band alignment and strong optical anisotropy, the device also exhibits FE-dependent photocurrent and broadband polarization sensitivity with a dichroic ratio up to 869, which provides it with huge potential for the realization of an all-in-one optoelectronic architecture with sensing, memory, and processing functions.