The solid phase part of the Hg-Zn-Te-O equilibrium phase diagram has been estimated from thermodynamic calculations. It was found that, contrary to other A²B⁶ tellurides, ZnTe possesses a preferable oxidation of metal, leaving elemental tellurium at the native oxide-ZnTe interface. It is shown that, as a result, the electrical properties and thermal stability of the native oxide-Hg_1-xZn_xTe interface are superior to those of the native oxide-Hg_1-xCd_xTe interface. Hence, in terms of the interface properties, Hg_1-xZn_xTe seems to be a better material for infrared device applications. It is also demonstrated that for a semiconductor compound the equilibrium phase diagram qualitatively determines the electrical properties of the native oxide-semiconductor interface.