Effects of rapid-thermal-annealing (RTA) cover material on the properties of GaNAs/GaAs triple quantum wells (QWs) grown by chemical beam epitaxy (CBE) are studied in detail. Si wafer, GaAs wafer, and GaAs layer grown on GaAs substrate at low temperature are used as RTA cover materials. The results show that RTA cover material exerts significant influence on the properties of the QWs. The QWs using GaAs layer show not only the lower root mean square (RMS) roughness of sample surface but also the lower photoluminescence linewidth compared with those using GaAs wafer and Si wafer. The best RTA cover material is neither GaAs wafer nor Si wafer. The best RTA cover material is GaAs layer grown at low temperature from the viewpoints of both surface morphology and optical properties. The results obtained in this work are helpful for quality improvement of (In)GaNAS using RTA. (C) 2004 Elsevier B.V. All rights reserved.