Design and development of double-layer anti-reflection coating for HgCdTe based mid-wave infrared detector

A novel design and development of double-layer antireflection coating (ARC) is presented here for back side illuminated HgCdTe based mid- wave infrared (MWIR) detector. Reflectance of infrared radiation in the CdZnTe/HgCdTe structure is simulated to achieve optimum material and thickness of antireflection coating layers for mid- wavelength range. A polishing process for the surface qualification of CdZnTe material prior to deposition of layers has been developed using different chemical treatments and ellipsometric characterisation techniques. The desired ellipsometry parameters (i.e. 4.0<Ψ < 4.6 and 145<Δ<150) of CdZnTe surface is achieved with the polishing of Br 2 -metanol solution. The optimized ARC layers of YF 3 and ZnS are deposited on the back side of CdZnTe surface and measured the reflectance by Fourier-Transform Infrared (FTIR) technique. The reflectance of below 2% is observed in the backside illuminated YF 3 /ZnS/CdZnTe/HgCdTe structure for mid-wave infrared range, which is similar with the simulated results. Thus, an improvements as well as new functionalities are implemented in infrared sensors by depositing optimum stack of thin film layers.