The influence of an InGaN underlying layer under InGaN multiquantum wells (MQWs) on the optical properties was investigated. Two MQW structures with and without underlying layers were prepared by MOCVD on sapphire substrates. Optical properties were characterized by means of temperature-dependent photoluminescence (PL), PL excitation (PLE), space-resolved micro-PL (P-PL) and time-resolved PL (TRPL) measurements. From the micro-PL mapping and temperature-dependent PL results, a more uniform emission distribution and an internal quantum efficiency of about 45% have been achieved with an InGaN layer below the MQWs. We observed an enhancement of both PL intensity and lifetime at room temperature for the InGaN MQWs grown on an InGaN underlying layer, compared to the InGaN MQWs without InGaN underlying layer. (c) 2005 Elsevier B.V. All rights reserved.