Design and development of four-layer anti-reflection coating stacks (ZnS and YF3 thin films) for HgCdTe-based mid-wave infrared detectors

The four-layer anti-reflection coating (ARC) film stacks (consisting of four layers of zinc sulphide (ZnS) and yttrium fluoride (YF3) materials with an optimized thickness of 699 ± 2.6 nm) were grown on the backside of the HgCdTe (mercury cadmium telluride)-CdZnTe (cadmium zinc telluride) assembly (i.e., CdZnTe substrate) using the thermal-evaporation deposition technique. Successively, the characterization tools like atomic force microscope, X-ray diffractometer, energy dispersive X-ray spectrometer, and scanning electron microscope were utilized to realize the optimized ARC film stacks. ARC stacks (ZnS/YF3/ZnS/YF3) with cubic zinc blende phase and preferred orientation (111) were confirmed. The desired surface morphology (dense and low roughness), elemental composition (purity), and micro-structural features (reasonable grain size and material continuity) of ARC films were achieved. The optimized films were further examined through their utilization in the fabrication of two similar ARC stacks/structures with a configuration of YF3/ZnS/YF3/ZnS/CdZnTe–HgCdTe and Fourier Transform infrared spectrometer was used to measure their reflectance. ARC film stacks (with remarkably thin film thickness and good repeatability) have reduced the reflection of HgCdTe–CdZnTe assembly to a minimum value from 22% to