We report on the effect of strain relaxations induced by lift-off in an InGaN/GaN multiple quantum wells (MQWs) blue light-emitting diode (LED) structure grown by metal-organic chemical vapor deposition (MOCVD) on a 150-mm diameter Si (111) substrate. To manage the lattice strain and, meanwhile, filter the threading dislocations, an AlN nucleation layer followed by a fourfold-step-graded AlGaN buffer together with multiple low-temperature AlN interlayers hasbeen employed, which results in a crack-free growth of 4.9-mu m GaN on Si (111) in the studied LED structure. High-resolution x-ray diffraction (HRXRD) and micro-Raman spectroscopy reveal that MQWs are coherently grown on the GaN layer while the GaN layer is tensile strained on the Si (111) substrate. Lift-off by wet-chemical etching results in phonon softening of both the top-layer GaN and the InGaN within the QWs: meanwhile, a red-shift of similar to 11 meV in the photoluminescence (PL) from the MQWs accompanied by a significant decrease ( > 4.9 times) in the PL-peak decay time is observed at room temperature. These observations are discussed and associated with the lift-off induced strain relaxations, which change the wafer curvature that in turn results in redistribution of in-plane stresses along the growth direction in the GaN-on-Si LED structure. (C) 2014 Elsevier B.V. All rights reserved.