Antireflective characteristics of Ge1−xCx films on sub-wavelength structured ZnS surfaces

Abstract Antireflective sub-wavelength structures (SWSs) combined a Ge1−xCx coating on Zinc sulfide (ZnS) can enhance the long-wave infrared transmission and durability of ZnS, which have the potent for practical applications. We have investigated the antireflective characteristics of Ge1−xCx sub-wavelength periodic hole structures on ZnS through the Fourier modal method (FMM) for application with normally incident, randomly polarized, 10.6 μm wavelength. Then according to the results, we have successfully fabricated the sub-wavelength periodic square hole structures with Ge0.05C0.95 films on one side of ZnS. A substantial transmittance improvement for bare ZnS in the 8–12 μm spectral region was obtained.