The photo-electric characteristics of tunnel MIS photo-detectors based on Hg 1−x Cd x Te for x ≈ 0.2 are presented. In order to reduce or eliminate Fermi level pinning, a passivation dielectric layer with thickness allowing for free carrier tunneling was grown on the metal-semiconductor interface. Dielectric layers composed of native oxides, native fluorides, SiO 2 or Al 2 O 3 were investigated. Values as high as 6.2 A W −1 for spectral responsivity and 5.3 × 10 10 cm Hz 1/2 W −1 for specific detectivity were obtained.