Microstructured Surfaces on LiTaO -Based Pyroelectric Infrared Detectors

Reflections of the incident radiation from the sensor surface are a major problem in enhancing the performance of pyroelectric infrared detectors. This paper reports on the approach to reduce these reflections by patterning the sensor surface of lithium tantalate (LiTaO₃)-based infrared detectors with subwavelength structures. These structures provide a better refractive index matching from air to sensitive material and, therefore, minimize reflections from the sensor surface. First of all, a multi-layer model is considered to describe the optical behavior of LiTaO₃ surfaces with subwavelength structures. As a result, design criteria for the structure dimensions are derived allowing elimination of a significant portion of surface reflections. The validity of the model could be proofed experimentally. The fabrication of microstructured LiTaO₃ surfaces is done by either a simple lapping process or standard contact lithography with subsequent ion beam milling. As a result, it was possible to enhance the responsivity of LiTaO₃-based infrared detectors up to 15%.