Close-spaced isothermal vapor phase epitaxy (VPE) was used to grow quaternary Hg1−x−yCdxZnyTe epillayers on Cd1−zZnzTe substrates. Composition, resistivity, and carrier concentration depth profiles were determined in the epilayers. p-n junctions were produced from material with appropriate properties using the Hg diffusion method. The junctions showed excellent I-V characteristics and high spectral detectivities.