High‐Barrier‐Height Ti₃C₂T_x/Si Microstructure Schottky Junction‐Based Self‐Powered Photodetectors for Photoplethysmographic Monitoring

Abstract A high Schottky barrier height (Φ_B) is one of the essential prerequisites for achieving high‐performance self‐powered Schottky‐barrier diode (SBD)‐based photodetector. The Φ_B value is predominantly determined by the metal function and interface quality of the metal/semiconductor contact. 2D MXenes with adjustable work functions and dangling bond‐free properties are promising building blocks for constructing self‐powered SBD with high Φ_B. Herein, a novel Ti₃C₂T_x MXene/Si hexagonal microhole array (SiHMA) van der Waals SBD is developed for the first time via a feasible solution process. Significantly, the device possesses a large Φ_B up to ≈1.07 eV, which is among the highest for the Si‐based SBD. In consequence, the Ti₃C₂T_x/SiHMA SBD yields a large responsivity up to 302 mA W⁻¹ and detectivity as high as 5.4 × 10¹³ Jones in a self‐powered model, surpassing the performance of most 2D material/Si photodiodes reported to date. Furthermore, it is demonstrated that featured and reliable fingertip photoplethysmogram (PPG) signals can be detected using the self‐powered SBD, enabling us to further accurately extract the heart rate (HR), and blood pressures (BP) using the PPG‐only method. This work paves the way for the construction of high‐performance MXenes‐based self‐powered SBDs for health monitoring.