The wide bandgap alloy Zn0.2Mg0.8S0.64Se0.36 has recently been grown by molecular beam epitaxy (MBE) and been shown to be oxidation and acid resistant. This makes it attractive either as a replacement or adjunct to MgS in II-VI multilayers. In this paper we compare the structural and optical properties of MBE grown multilayer structures containing Zn0.2Mg0.8S0.64Se0.36 to those grown with the quaternary alloy replaced by MgS. Cross-sectional high-resolution transmission electron microscopy (HRTEM) and X-ray interference spectra of ZnSe/Zn0.2Mg0.8S0.64Se0.36/ZnSe multilayers show the Zn0.2Mg0.8S0.64Se0.36 layers are of good crystal quality and do not phase segregate. Layer interfaces are seen to be flat and Zn0.2Mg0.8S0.64Se0.36 does not introduce defects into the overlying ZnSe. Atomic force microscopy shows the surface of a 30 nm Zn0.2Mg0.8S0.64Se0.36 layer is atomically flat, in contrast with similar MgS layers, which show pronounced I D surface ridges, indicating that the Zn0.2Mg0.8S0.64Se0.36 layers have not started to relax. ZnSe quantum wells grown with Zn0.2Mg0.8S0.64Se0.36 barriers show 77K photoluminescence comparable in wavelength and intensity to ZnSe wells of similar thickness grown with MgS barriers. This has allowed us to demonstrate the use of the quaternary alloy, which resists oxidation in place of MgS in multilayer structures. (C) 2008 Elsevier B.V. All rights reserved.