is mounted in a case adapted so that the photons 100 to be detected illuminate the p zone for this the thickness of the order of 20 u03bcm of the epitaxy zone 21 has been chosen so as to allow complete absorption of the photons in the vicinity of the junction the photodiodes thus obtained have a small dark current less than 0 1 a cm2 for the quality of the hg 1 x cd x te crystal the strict control of the surface conditions and the low doping used mean that the concentrations in the vicinity of the junction are small which results in reducing the dark current related to the tunnel effect moreover the excess noise factor x not to be confused with the molar fraction x related to the avalanche multiplication is small this is due to the fact that for the range of molar fractions considered the ratio between the coefficient of ionization of holes u03b2 and the coefficient of ionization of electrons u03b1 is very much less than 1 and to the fact that the photodiode is illuminated from the p side in the article 34 ga 1 x al x sb avalanche photodiodes resonant impact ionization with.