Wavelength-dependent tri-state waveform modulation in self-powered n-Si/Au nanoparticles/CdS heterojunction photodetectors

Photoresponse waveforms visually depict the charge carrier dynamics in photodetection and serve as a means of conveying optical information, analogous to the photoresponse amplitude and polarity. However, the waveforms of most photodetectors are frequently overlooked in applications due to the challenge of distinctly differentiating them. Herein, three distinct waveform patterns that respond to different wavelengths across the near-ultraviolet to near-infrared spectrum is realized by a self-powered n-Si/Au nanoparticles/CdS heterojunction photodetector. This wavelength-dependent tri-state response combines dual-polarity steady-state photocurrents and transient spike currents, which arise from synergistic effect of several mechanisms, including selective light absorption, opposing built-in electric fields, the light-induced pyroelectric effect in wurtzite CdS, and the localized surface plasmon resonance of Au nanoparticles. The unique ability of wavelength-dependent tri-state response facilitates waveform-modulated visible light communication, where RGB primary color lights are employed concurrently as the transmission medium, effectively doubling the information transmission rate.