A high-performance broadband double-junction photodetector based on silicon nanowire arrays wrapped by silver nanoparticles for low-light imaging

Abstract

Highly sensitive silicon-based nano-structure photodetectors have attracted tremendous attention in night vision imaging. However, most reported photodetectors suffer from large dark current, low detectivity and narrow operating waveband, which greatly limit their application in low-light and broadband detection. Herein, an NN⁺/MS double junction enhanced photodetector based on silicon nanowire (SiNW) arrays wrapped by silver nanoparticles has been fabricated. The light confinement effect and photogain in the SiNW arrays ensure high sensitivity to weak light, and the built-in electric field formed NN⁺ junction effectively accelerates carrier separation and suppresses dark currents. Meanwhile, plasmonic hot electrons generated in Ag nanoparticles after excitation could be emitted over MS junctions to achieve superior response currents and obvious sensitivity to near-infrared illumination. As a result, the double junction photodetector exhibits an ultrabroad spectral response ranging from 254 nm to 2200 nm in the self-driven operation mode, which not only enables a peak responsivity of 2.2 × 10³ mA W⁻¹, an outstanding specific detectivity up to 5.1 × 10¹⁴ cm Hz^1/2 W⁻¹ and an ultralow dark current density of 6 × 10⁻¹¹ A cm⁻², which are exceedingly better than those of the existing silicon-based devices, but also endows it with a rapid response speed with a rise/fall time of 25/62 μs at 980 nm. More importantly, the device shows a high low-light sensitivity to starlight irradiation (1.4 × 10⁻³ lux) due to photogain and sharp imaging capability under low-light conditions. This work provides a potential strategy for fabricating high sensitivity and broadband photodetectors for night vision imaging.