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

Photoresponse waveforms visually describe the charge carrier dynamics in a photodetector (PD) and serve as a means of conveying optical information, analogous to the photoresponse amplitude and polarity. Nevertheless, the waveforms of most photodetectors are frequently neglected due to the difficulty of distinguishing them. Herein, three distinct waveform modes are realized in a self-powered n-Si/Au nanoparticle/CdS heterojunction photodetector, corresponding to different wavelengths from the near-ultraviolet to near-infrared spectrum. This wavelength-dependent tri-state photoresponse is a selective combination of dual-polarity steady-state photocurrents and transient spike currents, which arise from the synergistic effects of several mechanisms, including selective light absorption, opposing built-in electric fields, light-induced pyroelectric effect of wurtzite CdS, and localized surface plasmon resonance of Au nanoparticles. The working principle is systematically verified, and the threshold CdS thickness for tri-state photoresponse is revealed. Notably, the unique property of wavelength-dependent tri-state photoresponse offers a pathway for RGB waveform modulation in visible light communication.