We report on the growth conditions of AlInN layers grown on free-standing GaN substrates. We found that an average indium content of similar to 20% is needed to obtain defect-free AlInN/GaN multilayers. This is larger than the commonly accepted value of 18% for lattice-matched condition. A model where tensile strain at the GaN/AlInN interface is induced by indium surface segregation occurring in AlInN layers is proposed to explain this discrepancy. A high In/Al flux ratio is shown to reduce this effect and allowed obtaining a defect-free AlInN/GaN Bragg reflector with a peak reflectivity of 99.6% suitable for vertical cavity light emitting devices. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3586767]