Intrinsic Hot-Electron Response Enabled Telecom-Band Ultrafast Silicon-Integrated van der Waals Photodetectors

Abstract

Near-infrared photodetection is vital in the fields of optical telecommunications, medical diagnostics, and consumer electronics. However, the bandgap of silicon limits its intrinsic spectral response to wavelengths below approximately 1100 nm, preventing direct detection in these sub-bandgap regions. Integrating silicon with plasmonic structures enhances electromagnetic fields and enables hot-electron (HET)-assisted sub-bandgap detection via localized surface plasmon resonance, yet isolating the intrinsic response of hot electrons remains largely unexplored, impeding the understanding and advancement of HET devices and their architectural design. In this study, we demonstrate switchable photoelectric mechanisms between HET transfer and photovoltage effect in a WO3–x/graphene/Si sandwiched photodetector. Notably, the intrinsic HET infrared response was elucidated through the analysis of power-dependent photocurrent (PC) evolution and transient absorption measurements spectroscopy. The direct transfer of electrodes, graphene intercalation layer, and WO3–x arrays endows a defect-free van der Waals contact device configuration. Combined plasmonic HET transfer achieves both fast response with a speed of 430 ns (rise time) and an extended detection range to 1550 nm, which is faster than many previously reported low-dimensional-material/Si photodetectors. The experimental results reveal distinct PC behaviors on either side of silicon’s cutoff wavelength, providing clear evidence of HET photoelectric conversion. This study provides valuable insights into the underlying mechanisms of HET optoelectronics and offers a pathway for developing high-performance sub-bandgap infrared photodetectors.