Current developments for type-II superlattice imaging systems

Abstract

InAs/GaSb-based type-II superlattice photodiodes have considerably gained interest as high-performance infrared detectors. Beside the excellent properties of InAs/GaSb superlattices, like the relatively high effective electron mass suppressing tunneling currents, the low Auger recombination rate, and a high quantum efficiency, the bandgap can be widely adjusted within the infrared spectral range from 3 - 30 μm depending on the layer thickness rather than on composition. Superlattice growth and process technology have shown tremendous progress during the last years. Fully integrated superlattice cameras have been demonstrated by several groups worldwide. Within very few years, the InAs/GaSb superlattice technology has proven its suitability for high-performance infrared imaging detector arrays. At Fraunhofer IAF and AIM, the efforts have been focused on developing a mature fabrication technology for bispectral InAs/GaSb superlattice focal plane arrays for a simultaneous, co-located detection at 3-4 μm and 4-5 μm in the mid-wavelength infrared atmospheric transmission window. A very low number of pixel outages and cluster defects is mandatory for dual-color detector arrays. Sources for pixel outages are manifold and might be caused by dislocations in the substrate, the epitaxial growth process or by imperfections during the focal plane array fabrication process. Process refinements, intense root cause analysis and specific test methodologies employed at various stages during the process have proven to be the key for yield enhancements.