Change in the Reflection of the a-Si Film on the Surface of Al–4%Cu/Si in the Visible Range during Low-Energy Sputtering in Argon Plasma

In this work, a two-layer thin-film structure was investigated as a selective absorber based on the Fabry–Perot resonance in the visible wavelength range. A structure comprising 20 nm thick layers of amorphous silicon and 200 nm thick layers of aluminum doped with copper (4%) was deposited on a single-crystal silicon wafer using magnetron sputtering. Precision argon ion sputtering in the inductively coupled plasma controlled by a laser interferometer was used to obtain experimental samples with silicon thicknesses ranging from 20 to 11.6 nm in 2.8 nm increments. The experimentally observed shift of the resonance absorption peak from 590 to 440 nm with decreasing a-Si thickness leads to a clearly visible change in surface color. The experimental and calculated reflectance spectra were in good agreement. Almost complete absorption is observed in the wavelength range of 550–650 nm, resulting in the bright surface color.