A IDCA system with internal nBn photo-detector comprising: a photo-absorbing layer comprising an n-doped semiconductor exhibiting valence band energy level; a barrier layer, a first side of the barrier layer adjacent a first side of the photo-absorbing layer, the barrier layer exhibiting a valence band energy level substantially equal to the valence band energy level of the doped semiconductor of the photo absorbing layer; and a contact area comprising a doped semiconductor, the contact area being adjacent a second side of the barrier layer opposing the first side, the barrier layer exhibiting a thickness and conductance band gap sufficient to prevent tunneling of majority carriers from the photo-absorbing layer to the contact area, blocking the flow of thermalized majority carriers from the photo-absorbing layer to the contact area. Alternatively, a p-doped semiconductor is utilized, equalizing barrier conductance band energy levels and photo-absorbing layers.