Broadband Polarization-Gated Bipolar Photoresponse in a Twisted Anisotropic Heterojunction for a Multifunctional All-Optical Logic Gate and Miniaturized Spectrometer.

A bipolar photoresponse is essential for all-optical logic and neuromorphic computing yet remains challenging to achieve with precise tunability, fast response, and broadband operation within a single device. Here, we report a polarization-gated reversible bipolar photoresponse enabled by a twisted black phosphorus (BP)/BiOSe/BP van der Waals heterostructure. The bipolar photoresponse arises from the combined effect of dual oppositely oriented built-in electric fields in back-to-back BP/BiOSe heterojunctions and anisotropic absorption of BP. This twist-configured heterostructure produces a broadband bipolar photovoltaic response spanning 1000-3500 nm with excellent stability. Benefiting from the photovoltaic effect, the device achieves a fast response time of 4.3 μs and low noise equivalent power of 47 pW Hz. As a proof of concept, the bipolar photodetector enables six all-optical logic operations and a miniaturized spectrometer (1000-1600 nm) via reconstruction algorithms. This work presents an electronic-free architecture for all-optical logic and neuromorphic computing within polarization-gated bipolar devices.