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

Abstract

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.