Hot Electron Harvesting via Photoelectric Ejection and Photothermal Heat Relaxation in Hotspots-Enriched Plasmonic/Photonic Disordered Nanocomposites

The ability of plasmonic nanostructures to harvest photons beyond the traditional band-to-band photovoltaic conversion of semiconductors has stimulated intensive research activities in hot electron. As an emerging strategy for energy harvesting, photodetection and photocatalysis, realization of broadband and efficient plasmonic absorption with easily constructed metal-semconductor (M-S) nanosystems is essential for improving its photoelectric efficiency, while minimizing the cost and complexity of fabrication. Here, we report an approach for near-infrared (NIR) photodetection by combining the randomly and densely packed photonic nanostructures with ultrathin plasmonic coatings. Relying on the Au covered disordered silicon nanoholes (SiNHs) M-S platform, the efficient plasmonic absorption, strong field localization and together with random nature facilitate the broadband photon-energy conversion from both photoelectric hot electron ejection and photothermal hot electron relaxation. Spectral-and time-resolved studies reveal that the proposed Au-SiNHs device is capable of tracking fast varying NIR signals via hot electron emission process, with a photoresponsivity around 1.5-13 mA/W at wavelengths ranging from 1100 to 1500 nm. With a detailed theoretical analysis based on phenomenological model, different loss mechanisms involved in the hot electron related photoelectric process were described quantitatively and a large improvement potential was identified in the proposed hot electron harvesting platform. In addition, we demonstrated that the closely distributed random voids and tips in the Au-SiNHs structures enable the formation of a substantial amount of hot-spots that can significantly elevate the local temperature through the relaxation of the nonejected hot electrons and, therefore, generate the obvious photothemal mediated photoresponse under voltage driven conditions.