Black Silicon Revisited as an Ultrabroadband Perfect Infrared Absorber over 20 μm Wavelength Range

Black silicon properties are investigated in the wavelength range extending from 0.2 to 25 mu m with a focus on the mid-infrared (MIR). It is demonstrated that concurrently increasing the initial level of doping of bare silicon, with given limits, enables reaching even higher absorptance and higher spectral range. Unprecedented light absorptance levels are obtained on black silicon with up to 99.5% in the spectral range from 1 to 8 mu m and above 90% until 20 mu m, leading to ultrabroadband, ultrablack silicon surfaces. The synergetic effects of morphology and volume doping are elucidated; in particular, how the high aspect-ratio of conical nanostructures plays a crucial role. The experimental findings are analyzed with numerical simulations involving plasmonic effects of highly doped silicon and supported by tomographic processing of microscopy images. Guidelines and corresponding manufacturing routes are provided by which ultrabroadband, ultrablack silicon surfaces can be obtained within minutes of plasma processing, with no need for further functionalization. With the scalable manufacturing involving solely pure silicon, the resulting ultrabroadband perfect absorbers should be of benefit for large-scale deployment of radiative cooling devices, blackbody infrared light sources, and infrared radiation sensing.

Automated summary

The properties of black silicon are investigated in the mid-infrared wavelength range, with unprecedented levels of light absorption achieved. The experimental findings demonstrate that increasing the initial level of doping of bare silicon can significantly enhance both absorptance and spectral range. The synergistic effects of morphology and volume doping, particularly the role of high aspect-ratio conical nanostructures, are elucidated.