Strongly Adherent Radiation Hard Anti-Reflection Coatings for Mercury-Cadmium-Telluride Detectors

Mercury cadmium telluride (MCT) is the basic material for infrared detector and LWIR sensor applications. Anti-reflection coatings are applied on the backside of the substrate for preventing the radiation damage. However, the useful lifetime ofanti-reflection coatings is significantly reduced upon exposure to solarization. During the Phase I research, Surmet Corporation proposes to develop radiation hardened anti-reflection nano-structured coating compatible with mercury-cadmium telluride (MCT)for long-wavelength infrared (LWIR) sensor applications. Two variations of this coating will be deposited using Surmet's innovative plasma vapor deposition technique which allows the easy manipulation of process parameters to achieve coating with tailoredapplication oriented properties. Excellent adhesion, provided by tailored interfaces combined with negligibly small deposition residual stresses and the micro conformal nature, make these coatings ideal candidates to survive the extreme thermal loadsexperienced during radiation exposure. The coatings will be characterized in terms of coating purity, adherence to MCT, radiation damage and optical transmission in order to determine their suitability for the intended application. Two coating compositionssuitable for the intended application will be presented to MDA program manager at the end of Phase I work in order to demonstrate the feasibility of the proposed concept. Optimization of the coating process and further characterization will be carried outduring subsequent Phase II work in consultation with the program manager. The proposed effort to develop anti-reflection coatings compatible mercury-cadmium-telluride for improved resistance to radiation damage will significantly improve the performanceof LWIR sensor systems in outer space environments. Development of these radiation hardened coating(s) will also have the potential to be extended for use as anti-reflection coatings in other visible and infrared optical applications such as eximer lasers.