Double-crystal X-ray rocking curve (DCRC), Auger electron spectroscopy (AES), transmission electron microscopy (TEM), photoluminescence (PL), and Raman scattering measurements on undoped and doped ZnSe epitaxial films grown on GaAs (100) substrates by molecular beam epitaxy were performed to investigate the structural and optical properties of the ZnSe films. From the DCRC analyses, the grown layer was found to be a ZnSe epitaxial film with high quality. The results of TEM measurements showed that the misfit dislocations of the nitrogen-doped ZnSe thin films was reduced in comparison with those of the undoped ZnSe films. The PL spectra of the nitrogen-doped ZnSe epilayer was dominated by donor-acceptor pair recombination and by a sequence of its longitudinal optical phonon replicas. Raman spectroscopy measurements showed that there was a lattice mismatch between the ZnSe epitaxial layer and the GaAs substrate and that a plasma-phonon coupling mode existed together with its characteristic longitudinal optical phonons. These results indicate that the ZnSe epitaxial films grown on GaAs hold promise for applications as buffer layers for the growth of Zn1-xMgxSySe1-y.