A brief report will be given on the structural investigation and the growth of single layers, quantum wells (SQWs) and superlattices (SLs) of ZnCdSe and ZnSSe on GaAs(001) by MOVPE. Crystalline quality, stoichiometry, strain and other structural parameters were determined by high-resolution X-ray diffraction (HRXRD). Lattice relaxation of ZnSSe was investigated and the influence of a ZnSe buffer will be discussed. Dislocation structures have been investigated by transmission electron microscopy (TEM). The dynamical scattering theory was utilized to obtain best fits to measured X-ray rocking curves. Reciprocal space maps were recorded to analyze the unit cell distortion and to obtain information about the degree of relaxation.