This paper is a discussion of the influence of heterojunction barriers on minority-carrier hole transport in wide band gap p+ on narrow gap n HgxCd1-xTe diodes that are illuminated from the n side. We have simulated detectors with 10.5 μm cut off wavelengths at 80 K by numerically solving the coupled transport and continuity equations for electrons and holes with Poisson’s equation. Parameters in the modeling include the composition of the p+ cap layer, the composition grading width, the doping of the base layer, temperature, and detector bias. The modeling predicts that the ratio of the quantum efficiency in a device with a barrier height of 2kT to that of a detector with no barrier is 0.95, while a 4.5kT barrier gives a value of 0.5. The model calculations have been qualitatively confirmed by experimental measurements of x=0.42/0.22 and 0.30/0.22 heterojunctions in which the doping in the low band gap n layer was varied to adjust the height of the heterojunction barrier.