Broad band enhanced infrared light absorption of a femtosecond laser microstructured silicon

Absorptive properties of surface-structured silicon prepared by femtosecond laser pulses irradiating in SF6 or N2 are measured in a wide wavelength range of 0.3–16.0 μm. The SF6-prepared surface-structured silicon shows enhanced light absorptance up to 80% or more in the entire measured wavelength range. The absorptance for N2_prepared surface-structured silicon in the wavelength range of 9–14 µm is similar to that of a SF6-prepared sample, although it decreases to about 30% in the wavelength range of 2–7 µm. Light absorption varies with the height and density of the spikes formed on silicon surfaces.