The surface and interface structures of ZnTe epilayers grown by molecular beam epitaxy on GaSb (001) substrates under different conditions have been investigated by high resolution x-ray diffraction and grazing incidence scattering. Reciprocal space mapping around the symmetrical diffraction reciprocal point 004 and asymmetrical diffraction point 1¯1¯5 showed that the ZnTe epilayers, in the samples investigated, were fully strained to the substrate. The crystalline quality of the ZnTe epilayer grown on a substrate annealed in a Zn flux was very good, while evidence for an interfacial layer, of thickness varying from 2–20 nm, was found when the substrate was annealed in a Te flux prior to growth. This is attributed toGa2Te3formation at the interface. The interfacial layer roughens the interface and surface, and both crystal truncation rod measurements and grazing incidence x-ray reflectivity show the surface roughness to be about 4 nm. Such a rough surface and interface is also inferred from the broader distribution along the transverse direction in reciprocal space maps. A shorter lateral correlation length is found for the roughness of the sample containing the interfacial layer. The disappearance of interference fringes is attributed to nonuniformity of the interfacial layer. ©1997 American Institute of Physics.