A new silicide/silicon IR detector is presented which has the potential for multicolour detection due to the tunability of its photoresponse. This tunable internal photoemission sensor (TIPS) fabricated using the Ir/Si/ErSi2 system, consists of two back–to–back Schottky diodes separated by a thin undoped Si layer. The two metals have different Schottky barrier heights so that the depleted Si forms an asymmetrical potential barrier to the carriers photocreated in each metallic film. The photocurrent flowing between the two metallic films is therefore strongly dependent on the shape and height of the effective potential barrier that can be varied by a bias applied between the two metallic electrodes. The Ir/Si/ErSi2 photoresponse and cut–off wavelength are indeed dramatically modulated when a small bias (less than 1 volt) is applied between the Ir and ErSi2 electrodes. The quantum efficiencies, measured in the 1 to 3 μm range, are comparable to the best obtained in Schottky and SiGe/Si internal photoemission detectors. A quantitative model derived from the Fowler formalism (by taking into account (i) the hole and electron photocurrents and (ii) the wavelength dependence of the photon absorption in each metallic film) fits all the experimental data over the whole range of photon energy and applied biases. The effective barrier heights thus measured as a function of applied bias are in good agreement with those deduced from activation energy analysis of the TIPS dark current and show that the cut–off wavelength can be modulated from 2.5 μm to more than 6 μm. Finally, electrical and photoresponse measurements on Cr/Si/SiGe(p+) structures (using the same TIPS mode of operation) also demonstrate the photoresponse tunability, thus combining the TIPS tunability with the extended wavelength range of operation (up to 10 μm) of SiGe/Si detectors.