Components and performance of graded Ge1-xCx:H coatings deposited by magnetron co-sputtering for IR wideband antireflection

Abstract

Ge1-xCx:H coatings have been studied as IR antireflection (AR) coatings on ZnS, but not well shown as graded ones for a wideband antireflection on ZnSe and Ge due to their component complexity. In this work, the steeper graded Ge1-xCx:H coatings were deposited by co-sputtering the C and Ge targets, their components were characterized by SIMS and Raman spectra, and their transmittances in the IR band of 0.7–14 μm were measured by FTIR. The results show that, in the coating deposited by the magnetron co-sputtering technology, the curve of Ge content could be described with a progressively steeper slope similar with the reported designs and functional groups are presented. With the coating, the highest transmittance in all ZnSe samples is 94.1% at the wavelength of 8.5 μm. A method of controlling different thicknesses on two sides of a ZnSe slab is used to obtain an even curve with the transmittance of almost above 80% in a very wide band of 3–11 μm. The peak transmittances of the Ge slab are 97% at 2.5 μm and 90% at 6.7 μm. The formation mechanism and performance modulation of the Ge1-xCx:H graded coating are discussed.