We report on the growth and characterization of InAs/InxGal..Sb strained-layer superlattices (SLS) designed with a photoresponse cut-off wavelength of IOlim. The structural parameters, layer thicknesses and compositions, were chosen to optimize the infrared absorption for a superlattice with an energy band gap of 120 meV. The energy band structure and optimized absorption coefficient were determined with an 8×8 envelope function approximation model. The superlattices were grown by molecular beam epitaxy and were comprised of 100 periods of 43.6Å InAs and 17.2Å In.23Ga.77Sb lattice-matched to the GaSb substrates. In order to reduce the background carrier concentrations in this material, superlattices grown with different substrate temperatures were compared before and after annealing. This set of superlattice materials was characterized using x-ray diffraction, photoresponse and Hall measurements. The measured photoresponse cut-off energies of 116 ± 6 meV is in good agreement with the predicted energy band gap for the superlattice as designed. The intensity of the measured mid-infrared photoresponse was found to improve by an order of magnitude for the superlattice grown at the lower substrate temperature and then annealed at 520 °C for 10 minutes. However, the x-ray diffraction spectra were very similar before and after annealing. The temperature dependent Hall measurements at low temperatures (<25K) were dominated by holes with quasi two-dimensional behavior. An admirably low background carrier concentration of 1×1012 cm−2 was measured at low temperature.