Results on Be diffusion during post-growth rapid thermal annealing at 750degreesC and 850degreesC in InGaAs, InGaAsP homostructures and InGaAs/InGaAsP heterostructures, grown by gas source molecular beam epitaxy, are reported. Profiles calculated with the kick-out model can be fitted to experimental secondary ion mass spectrometry profiles assuming Be to diffuse as neutral interstitial species. (C) 2003 Elsevier Science B.V. All rights reserved.