Different strain-balanced InGaAs/InGaAs multi-quantum wells (MQWs) were grown on (0 0 1) Inp to be used as active layers of thermophotovoltaic devices. Transmission electron microscopy (TEM) and high-resolution X-My diffraction (HRXRD) were performed to correlate the evolution of the layer interfaces from planar to wavy and the consequent nucleation of extended defects with the well and barrier compositions and thicknesses and the growth temperature. The existence of a critical elastic energy density for the wavy growth onset has been experimentally confirmed by changing both the well and barrier misfit and the multi-quantum well layer thickness. A decrease of the gowth temperature shifts the critical energy to higher values. An empirical model to predict the maximum number of layers that can be grown without modulations as a function of the strain energy stored in the MQW period and the growth temperature is presented and successfully applied for the growth of high quality 40 repetitions MQWs with a well misfit of about 1.5 %. (C) 2004 Elsevier B.V. All rights reserved.