Design and characteristics of high performance mid-wavelength type-2 superlattice sensors

2018
Oğuz, Fikri
Type-II Superlattices (T2SLs) are bandgap engineered structures that have attracted a lot of attention in the last couple of decades and is still some of the hot topics in infrared imaging applications. T2SLs are the most promising member of the quantum structured infrared family. By the end of maturity period of T2SLs, Focal Plane Array (FPA) level products have been released since a decade. Offering performance compatible with high-end infrared systems, yielding respectable results and still being open to further development make T2SL subjects worth to work on. The flexibility in design and the opportunity provided by nature of structures enable researchers and manufacturers to give their focus on this today’s world materials system. This thesis work covers the state of the art Mid-Wavelength Infrared Region (MWIR) InAs/GaSb Type-II Superlattice infrared technology in terms of design, fabrication, and characterization. Large format (640 x 512) and small pitch (15 µm) architecture are implemented for the fabrication of T2SL FPAs. The critical design parameters and design approaches for ultimate performance and reasons for capabilities of T2SLs to offer such performance are handled. After the presentation of detailed fabrication procedure and experimented fabrication methods, large area pixel level and FPA level characterizations are also discussed. The performance comparisons of experimented fabrication processes are demonstrated. With dark current modeling of large area T2SL diodes, the dominant dark current mechanisms for varying bias regions are clarified. With this modeling, our properly designed T2SL structure shows no tunneling dark current and is dominated only by detector shunt current at most of the bias regions. Electro-optical measurements yielded very satisfactory results. The optimized FPA which is a 15 µm pitch detector with cut-off wavelength of 4.92 µm yields 1.2 A⁄W peak responsivity and 30 mK Noise Equivalent Temperature Difference (NETD) with f⁄2.3 optics. The calculated quantum efficiency for this detector is larger than 60 %. Example images were acquired using optimized FPA device, and are provided in the thesis for demonstrative purposes.

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Citation Formats
F. Oğuz, “Design and characteristics of high performance mid-wavelength type-2 superlattice sensors,” M.S. - Master of Science, Middle East Technical University, 2018.