We have investigated ZnMgBeSe-quaternary wide-band-gap alloys grown by molecular beam epitaxy lattice-matched or moderately strained onto (0 0 1)-GaAs substrates, paying attention to preserve conditions compatible with the growth of other ZnSe-based compounds. Two-dimensional growth is obtained up to band gaps as high as 3.5eV, as measured by reflectivity, Intense and narrow photoluminescence is observed for all samples, up to 3.6eV. X-ray linewidths as narrow as 10 arcsec are obtained which compare very well with the substrate value of 7 arcsec. This reveals the high crystal quality of the epitaxial material. Our results show that this material is well suited for UVA detection.