High-efficiency narrow-band plasmonic hot electron conversion from nanoscale sodium–silicon heterostructures

Abstract

Plasmonic harvesting of hot electrons has stimulated intensive research activities for applications ranging from sub-bandgap photodetection to photocatalysis. Both high photoelectric conversion efficiency and tunable spectral response are pursued by manipulating resonant metal–semiconductor (M–S) nanostructures. Although noble plasmonic metals have been exclusively employed in hot electron conversion studies, exploring new materials may offer an additional degree of freedom to manipulate the hot electron generation, transport, and emission processes. In this paper, we propose to employ the low-loss alkali metal sodium as an alternate plasmonic material for developing a narrow-band resonant hot electron device. Based on a backside-illumination (BSI) configuration where plasmonic hot electrons generate locally at the M–S interface, the transport loss can be significantly suppressed. Thanks to its ultralow imaginary part of the permittivity, bringing Na into the BSI design allows for efficient shrinking of the resonant linewidth down to sub-20 nm. Another intriguing feature is that Na has more preferred electron density of state distribution for facilitating hot electron emission at the M–S junction. The optimized Na BSI device can yield a photocurrent responsivity up to 50 mA/W at a wavelength of 1400 nm as predicted by our electromagnetic simulation and theoretical model. Our study highlights that the alkali metal could be a promising alternative material for the development of high-Q resonant hot electron devices for near-infrared wavelengths.