WS2/MHS PdTe2/Si Mixed-Dimensional Heterojunction as Ultra-Broadband Photodetector for Health and Safety Monitoring.

Ultra-broadband photodetectors (UB-PDs) are essential in medical applications, public safety monitoring, and various other fields. However, developing UB-PDs covering multiple bands from ultraviolet to medium infrared remains a challenge due to material limitations. Here, a mixed-dimensional heterojunction composed of 2D WS₂/monodisperse hexagonal stacking (MHS) 3D PdTe₂ particles on 3D Si is proposed, capable of detecting light from 365 to 9600 nm. The exceptional performance of this photodetector is attributed to MHS PdTe₂ particles, which increase the specific surface area and enhance UV-to-NIR absorption of the 2D WS₂ nanofilm. At 980 nm (0 V), the device achieves a responsivity of 7.8 × 10² mA W^-1, a detectivity of 2.5 × 10¹³ Jones, and a sensitivity of 2.6 × 10⁸ cm² W^-1. The MHS PdTe₂ layer amplifies the built-in electric field and enhances heterojunction self-powered capability. This photodetector exhibits a high switching ratio (10⁴), a rapid response time (24.14 µs), and a significant photocurrent gain at zero bias. Its application in blood oxygen saturation analysis is demonstrated based on dual-wavelength photoplethysmography (PPG) at 650 and 905 nm, and infrared perspective imaging at 808 nm. Additionally, the device can differentiate materials based on their transmittance at 9600 nm. This research opens new avenues for the multifunctional use of UB-PDs.