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 micro-scope, X-ray diffractometer, energy dispersive X-ray spectrometer, and scanning electron microscope were uti-lized 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 < 1.0% within the mid-wave infrared spectral region, which further validates theoretically. Thus, the four-layer ARC film stacks are the effective reflection agent that could be used to fabricate high-performance HgCdTe infrared detectors.