Nanofabrication of silicon nanowires with high aspect ratio for photo-electron sensing

Abstract

Nanoscale silicon wires with high aspect ratio are beneficial in light harvesting for high responsivity in photoelectronic detectors. Reduction of wire width increases the surface-to-volume ratio, but introduces inelastic electron-boundary scattering caused by line edge roughness, limiting the photoconductivity at the same time. This paper is motivated by these structural effects on the device performance, aiming to develop the photoelectronic detectors with ultra-fine Si nanowires with high aspect ratio. Electron beam lithography assisted by Monte Carlo simulation was carried out on HSQ, which was used as etch mask for forming high aspect ratio Si nanowires by reactive ion etch. As narrow as 5 nm HSQ lines with the line edge roughness of sub-3.6 nm was achieved. Masked by the replicated HSQ lines, silicon nanowires with the width from 75 nm down to sub-10 nm and the aspect ratio of 30:1 were achieved through a dry etch process. Characterization of photo-electronic responsivity of the fabricated Si nanowires in visible wavelength demonstrates the maximum responsivity can be achieved in an optimized width with which the surface-to-volume ratio is balanced by the sidewall roughness. The milestone established in this work covers not only the technical advances of Si nanowires with high aspect ratio but also physical understanding of the structural effect on the device performance.