Carrier injection efficiency has been studied using multiple quantum well (MQW) LED structures in order to resolve the difficulty of p-n junction placement in nitride LEDs. Variation of an active QW position in MQW LEDs results in different emission efficiency and spectra. The difference mainly comes from carrier injection efficiency of MQW LED structures. The comparison of peak lambda in electroluminescence (EL) and photo-luminescence (PL) reveals the carrier distribution in active layers. EL and PL slope efficiencies in selective peak wavelengths indicate the performance of individual QWs for carrier injection and recombination. These efficiencies and brightness guide us towards the optimum number of QWs and the effective LED structures. (c) 2008 Elsevier B.V. All rights reserved.