We report on the development of a new structure for type II superlattice photodiodes that we call the "N" design. In this new design, we insert an electron barrier between InAs and GaSb in the growth direction. The barrier pushes the electron and hole wavefunctions towards the layer edges and under bias, increases the overlap integral by about 25% leading to higher detectivity. InAs/AlSb/GaSb superlattices were studied with density functional theory. Both AlAs and InSb interfaces were taken into account by calculating the heavy hole-light hole (HH-LH) splittings. Experiments were carried out on single pixel photodiodes by measuring electrical and optical performance. With cut-off wavelength of 4.2 mu m at 120 K, temperature dependent dark current and detectivity measurements show that the dark current is 2.5 x 10(-9) A under zero bias with corresponding R(0)A resistance of 1.5 x 10(4) Omega cm(2) for the 500 x 500 mu m(2) single pixel square photodetectors. Photodetector reaches BLIP condition at 125 K with the BLIP detectivity (D-BLIP(star)) of 2.6 x 10(10) Jones under 300 K background and -0.3 V bias voltage. (c) 2012 Elsevier B.V. All rights reserved.