The crystal quality of coupled double quantum wells (CDQWs) having different barrier structures was investigated by evaluating optical properties and structural interface quality. Photoluminescence (PL) spectra revealed that the CDQW samples with an AlAs/InAlAs combined barrier (CDQW(CB)) exhibited a narrower PL emission peak than those with an AlAsSb barrier. CDQW(CB) also showed the best excitation dependence of PL intensity. X-ray reflectivity (XRR) measurements revealed that better interface quality was confirmed in CDQW(CB). We conclude that CDQW(CB) has the best crystal quality among those evaluated. (C) 2015 Elsevier B.V. All rights reserved.