Atomic-force microscopy is used to investigate the distribution of the contact-potential difference (surface potential) in Cd x Hg 1 − x Te epitaxial films grown by molecular-beam epitaxy. Modification of the solid-solution composition near the V -defect results in a variation in the contact-potential difference. It is shown that the solid-solution composition varies by ∼0.05 (2.5 at %) towards increasing mercury content in the V -defect region, and a region of mercury depletion by 0.36 at % is observed at the V -defect periphery. From analysis of the surface-potential distribution, it is shown that the Cd x Hg 1 − x Te epitaxial film contains unform V -defects with a diameter less than 1 μm in addition to macroscopic V -defects.