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The first demonstration of InSb photodetector with nBn design is reported. The nBn structure, grown by molecular beam epitaxy (MBE) on InSb substrate, is built by using n-type InSb as absorber layer and InAlSb alloy as barrier layer. The nBn detector, showing cut-off wavelength of 5.4 µm at 77 K in photovoltaic mode, exhibits dark current density as low as 10 −9 A/cm 2 at −50 mV reverse bias, at least two decades lower than usual InSb photodiode.Introduction: InSb remains the most commonly used material for the fabrication of high-speed photodetectors operating in the midwave infrared (MWIR, 3-5 µm) spectral region. The pn junctions of InSb photodiodes are usually fabricated by impurity diffusion or ion implantation, and nowadays InSb large focal plane arrays in formats up to 2k × 2k with 15 µm pitch are commercially available [1]. The InSb devices have to be cooled to 77 K, and the performance begins to be significantly degraded at higher temperature of 90 K, which is undoubtedly a strong disadvantage for power consumption. To satisfy the well-known size, weight and power (SWaP) criteria and then increase autonomy, reduce system size and improve the reliability, it is necessary to enhance temperature operation without reducing performances. Recently, a new structure design, called nBn [2], was developed to reach the high-temperature operation by eliminating the bulk Shockley-Read-Hall generation-recombination (G-R) currents. The usual nBn design is made of an n-type absorber layer, a wide-bandgap barrier region followed by an n-type contact. The transport of electron majority carriers is then blocked by the barrier while hole minority carriers, created by the absorption of infrared radiation, can move across the device. This specific barrier detector architecture was successfully applied to InAsSb [3][4][5], InAs/GaSb superlattice [6,7], InAs/InAsSb superlattice [8] and HgCdTe [9] photodetectors. Consequently, nBn design is now considered as the quantum structure architecture suitable to achieve high operating temperature in the MWIR domain.In this Letter, we report the first results of InSb nBn detector using n-type InSb layer as absorber layer and strained wide-bandgap InAlSb layer as barrier layer.Experiment: The InSb nBn structure was grown by molecular beam epitaxy (MBE) on n-type (Te-doped) InSb (100)-oriented substrate using a Varian Gen II MBE reactor. Fig. 1 shows the schematic band diagram of the considered InSb/InAlSb/InSb nBn structure. It consists of a 400 nm Te-doped (∼4 × 10 16 cm −3 ) buffer layer followed by 1 µm-thick Te-doped absorption layer (∼1 × 10 16 cm −3 ), followed by 50 nm-thick non-intentionally doped InAlSb barrier layer and capped with a 200 nm Te-doped InSb layer (∼2 × 10 16 cm −3 ). 0 0.1 0.2 0.3 0.4 0.5 0.6 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 DE V1 DE V2 DE C1 In 0.85 Al 0.15 Sb InSb cap layer n-type n cap~2 x 10 16 cm -3 barrier layer non-intentionally doped (nid) InSb absorption layer n-type n abs~1 0 16 cm -3 V = 0 V T = 110 K energy, eV thickness, mm E F gradual composition ...