High–Performance Polarity–Reconfigurable Transistor and Photodiode via Asymmetric Transferred Schottky and Evaporated Ohmic Contacts

Reconfigurable Schottky–junction devices (SJDs) have emerged as a promising solution to the doping challenges in 2D materials by exploiting polarity switching between n–/p–type transistor and intrinsic–n–type (I–N)/intrinsic–p–type (I–P) diode. However, symmetric Schottky barriers at both contacts limit unipolarity and reduce on–current. Here, a polarity–reconfigurable device (PRD) is presented that combines transferred Au bottom electrode (BE)/WSe₂ Schottky contact with evaporated Ti top electrode (TE)/WSe₂ Ohmic contact. This design enables operation in four distinct modes n–/p–type FET and I–N/I–P photodiode, controlled by drain and gate voltages. The transferred Au BE introduces a space gap that shifts the Au Fermi level toward the center of WSe₂ bandgap and forms high Schottky barrier for both electrons and holes, while the evaporated Ti TE increases Fermi–level pinning and forms an Ohmic barrier. These asymmetric barriers allow unipolar carrier transport through TE/WSe₂ Ohmic barrier by blocking opposite carriers at BE/WSe₂ Schottky barrier. The PRD achieves on/off ratios >10⁶ in both FET modes, rectification >10⁶ with near–unity ideality, and fast ≈3 µs photoresponse in both photodiode modes. By combining devices with different polarities, complementary systems are created, including inverter circuit (gain of 38), reconfigurable NAND/NOR logic gate circuit, and optoelectronic device for in–sensor image processing.