Several field applications require extended short wavelength infrared (e-SWIR) band capabilities in future systems. It is highly desirable to design a next-generation FPA to overcome the deficiencies of e-SWIR imaging sensors. In recent years, Antimonide-based Type-II superlattices (T2SL) represent the most promising material system capable of delivering more producible, large-format, reduced pixel pitch, e-SWIR focal plane arrays (FPAs) for global observation applications. We propose to develop T2SL-based photodetectors and FPAs for NASA imaging and spectroscopy applications in the spectral band from visible to extended e-SWIR (0.4–2.5µm) with a very low dark current density. Using the highest quality material and a novel bandgap-engineering design and process, we will fabricate high performance photodetectors and FPAs through the e-SWIR region. In Phase I, we are going to continue to advance our previous work on design and structure of NIR and SWIR T2SL photodetectors and then demonstrate a novel e–SWIR uni-traveling carrier bandstructure–engineered photodetector design utilizing an optimum device structure and material(s) to achieve operation at 150K and above. We will simulate essential electrical and optical characteristics for a device that meets the performance requirements for low dark-current (<1×10-10 A/cm2) and high quantum efficiency (>70%) at 150K. Fabricate and test single element devices as proof of concept for future large format imager suitable for hyperspectral and atmospheric sensing. In this project, Northwestern University will collaborate with Nour, LLC to study and grow strain-balanced InAs1-xSbx/InAs and InAs/AlSb/GaSb Type-II superlattices with barrier structures for e-SWIR photodetectors. Using these superlattice structures, it is expected to achieve longer minority carrier lifetime and lower dark current densities. This will enable reduced imager cooling and significantly reduce size, weight and power of remote observation platforms.
To obtain high sensitivity over the entire 0.4-2.5 μm wavelength band, the usual approach is to use multiple detectors. This approach complicates the size and complexity of the imaging system for earth observation missions. For these missions, a single visible to eSWIR array is of special interest to NASA for global observations to study the world’s ecosystems, climate change, atmospheric monitoring and provide critical information on natural disasters such as volcanoes, wildfires and drought.