Antireflection Patterning of Si for InAsSb Nanowire Infrared Photodetectors

Abstract: The pattering of an optical surface with physical features like with very low reflectivity and high transmission of IR or visible light can be used e.g. for antireflective windows for solar cells and photodetectors. Here we present results on antireflective patterning of Si for back side illuminated InAsSb nanowire long wavelength IR (8-15 µm) photodetectors. Photolithography and dry etching techniques are used to pattern Si into uniform pillars and by using a Fourier transform infrared spectrometer we measure the transmittance. We use numerical simulations to aid the design of the dimensions of Si pillars. Results from transmittance measurements exhibit diameter dependent peaks that are in good agreement with the numerical simulations. The numerical results reveal that the transmission peaks are due to resonant wave guiding modes that enhance the coupling of light into the Si pillars. We have found that with the proper selection of pillar diameter a resonance enhanced transmission peak at specific wavelength can be achieved. We have found that the transmission of IR through bared Si is 53% which is independent of wavelength. Arrays of Si pillars with mean diameter 1.33 μm ± 36 nm show transmission peak at wavelength of 6.2 μm and array of Si pillars having mean diameter 1.42 μm ± 35 nm shifts the transmission peak at wavelength of 7.5 μm. Doughnut shaped Si hollow pillars are also observed as a result of photolithography. The transmission spectrum of Si hollow pillar arrays is also analyzed.