HgCdTe heterojunctions consisting of a wide band gap n-type Hg1−xCdxTe layer grown epitaxially on a narrow band gap p-type Hg1−yCdyTe substrate (x>y) were studied. The heterojunction transition region between x and y materials was found to be graded over distances of about 0.4 to 0.8 μm. The position of the p–n junction depletion layer within the graded transition region was the major factor controlling the heterojunction properties. When the depletion layer was located near the narrow band gap material, normal photodiode behavior was observed. When the depletion layer was at the center of the transition region or near the wide band gap material, a potential barrier was formed which inhibited minority carrier photocurrent originating in the p-type material from crossing the heterojunction. Qualitative energy band models based on the analysis of HgCdTe heterojunctions recently published by Migliorato and White were constructed to explain the observed results.