Controlling the Light Absorption in a Photodetector Via Nanowire Waveguide Resonances for Multispectral and Color Imaging

The responsivity spectrum of a photodetector is one of its key specifications. It ultimately originates from the combination of the absorption spectrum of the photosensitive region and the internal quantum efficiency. Many applications of photodetectors would benefit from an improved ability to tailor the responsivity spectrum. This is particularly true for color and multispectral imaging. The absorption spectrum of a bulk (unstructured) semiconductor is fixed however, being determined by its complex refractive index. Here, we review recent work that demonstrates that the absorption spectrum of a photodetector can be controlled via waveguide resonances in semiconductor nanowires. We discuss the physical interpretation for this phenomenon. We review work in which p-i-n photodiodes were incorporated into vertically oriented silicon nanowires, and then used for color imaging. We review work in which tandem-style photodetectors were demonstrated, with a p-i-n silicon nanowire photodiode formed above an n-i-p planar silicon photodiode. We review work in which narrowband photodetection across the visible-to-infrared was demonstrated using germanium nanowires. Finally, we describe related work in which silicon nanowires have been explored for other applications, namely solar cells.