Over the last years, superlattice (SL) related heterostructures based on the 6.1 Å materials family (GaSb, InAs and AlSb) have proven their great potential for high performance infrared (IR) detectors. The most interest is focused on short-period InAs/GaSb SLs, which offer a widely adjustable effective band gap (3-30 µm). A high effective mass and a low Auger recombination rate result in low dark currents in p-i-n InAs/GaSb SL photodiodes. A long minority carrier diffusion length enables IR-detectors with high quantum efficiency comparable to Cd_xHg_1-xTe.

At the Fraunhofer IAF a mature manufacturing process for mid-wavelength IR (MWIR, 3-5 µm) InAs/GaSb SL detector arrays has been established. The small volume production process is based on commercial 3”-GaSb substrates, a solid source multi-wafer molecular beam epitaxy system, a fully automated stepper lithography environment and inductively coupled plasma dry etching.

For the integration of SL detectors into closed-cycle cooled IR modules or cameras, Fraunhofer IAF cooperates with AIM Infrarot-Module GmbH. Monospectral as well as bispectral, dual-color SL IR-imagers with a noise equivalent temperature difference (NETD) down to around 10 mK have been realized.

Via a spatially and temporally coherent detection of two different wavelength ranges in the MWIR, the dual-color superlattice imagers enable fast and highly sensitive remote detection of carbon dioxide. Applications range from missile warning for airborne platforms to the study of gas exchange between the ocean and the atmosphere and its influence on climate change.

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