Harnessing the Interplay between Photonic Resonances and Carrier Extraction for Narrowband Germanium Nanowire Photodetectors Spanning the Visible to Infrared

At visible wavelengths, photodetection in three channels (red, green, and blue) enables color imaging. Yet the spectra of most materials provide richer information than just color, and therefore considerable interest exists for imaging with multiple spectral bands across the visible to infrared. This endeavor requires narrowband photodetection, which is generally achieved by combining broadband photodetectors with filters or spectrometers, but with added bulk and cost. Here we report, for the first time to our knowledge, vertical germanium nanowires as narrowband photodetectors. Our devices exhibit spectral response peaks that are as narrow as 40 nm and can be shifted from visible (-600 nm) to infrared (1600 nm) wavelengths by appropriate design. The spectral selectivity arises from the nanowires acting as waveguides and, surprisingly, is enhanced by radial narrowing of the carrier collection region due to surface recombination. The incorporation of germanium into integrated circuits in a high-yield and cost-effective manner is well-established, making our approach promising for many detection applications.