ZnS1−xTex(0<x<1)alloys grown on (100) GaAs substrates by molecular beam epitaxy are investigated using the x-ray diffraction and Raman scattering. The frequencies of long wavelength ZnTe-like and ZnS-like longitudinal optical phonons determined from Raman scattering show linear variation with the compositionx. The frequency of the zone-center optical phonons as a function ofxof theZnS1−xTexmixed crystal shows a typical two-mode behavior, which is in good agreement with the theoretical results from a modified random-element isodisplacement model.©1997 American Institute of Physics.