Defect-Engineered ITO/WSe2/W/Si Heterojunction for Broadband Photodetection and Waveform-Encoded Optical Communication.

Overcoming the inherent trade-offs among spectral bandwidth, sensitivity, and response speed in silicon-based photodetectors is critical for next-generation broadband optoelectronics. This work presents an ITO/WSe2/W/n-Si heterojunction photodetector designed to proactively harness interface defects, diverging from conventional defect-elimination paradigms. By synergistically regulating selenium vacancies via a tungsten (W) buffer layer and rapid thermal annealing, interface defects are transformed into performance-enhancing active sites. The engineered structure exhibits a 300-fold dark current suppression and broadens the spectral response to 532-2200 nm, effectively overcoming the band-gap limitations of WSe2 and Si. Notably, the device achieves a responsivity of 0.95 A/W (external quantum efficiency >222.4%) at 532 nm under a -2 V bias, while enabling self-powered optical imaging under weak illumination (0.01 mW) at 1550 nm. Furthermore, under high-frequency modulated illumination, the device exhibits a distinct bimodal transient waveform, characterized by an instantaneous spike that settles into a stable plateau. Exploiting this waveform, a waveform-encoded optical communication system is demonstrated for robust physical-layer data encryption. This study introduces an unconventional defect engineering approach and establishes a foundation for high-security optoelectronic integration.