we report nBn photodetectors based on InAs0.91Sb0.09 with a 100％cut-off wavelength of 4.75 μm at 300 K. The bandof an nBn detector is similar to that of a standard pin detector, but there is special wide bandgap AlAs0.08Sb0.92 barrier layer in the nBn detector, in which the depletion region of nBn detector exists. The nBn design has many advantages, such as low dark current and high quantum efficiency, because the nBn design can suppress the generation–recombination (GR) current that is the main composition of standard pin detector dark current. The constant slope of the Arrhenius plot of J0–1/T indicates the absence of the generation–recombination dark current. We fabricate an nBn detector with a quantum efficiency (QE) maximum of～60％under?0.2-V bias voltage. The InAsSb nBn detectors may be a competitive candidatefor midwavelength infrared detector.