Hg1−xCdxTe, grown by the alloy organometallic vapor phase epitaxy technique, was used in the fabrication of p‐n junction photodiodes. Hg1−xCdxTe layers, capped with a CdTe cap, were grown in a continuous run by the direct alloy growth process. These layers were p type due to column II vacancies, with a concentration of 3–4×1016/cm3. n‐type regions were obtained by selectively annealing the Hg1−xCdxTe layer after opening windows in the CdTe cap layer. Vertical p‐n junction diodes, with CdTe as the junction passivant, were thus formed in a planar configuration. Photodiodes, with cutoff wavelengths of 4.5 μm at 77 K, had R0 A products in excess of 9×107 Ω cm2.