It was shown that Te and Pb which segregated at the surface during epitaxial growth decreased and increased, respectively, the surface diffusion length. This indicated that, under the generic term of surfactant, there were 2 types of surface-segregating species which had opposite effects upon surface diffusion. It was suggested that the key parameter which governed the surfactant-induced modification of epitaxial growth kinetics was the reactivity of a given pair of surfactant and growing materials. According to this theory, it was predicted that surfactants which occupied interstitial surface sites (non-reactive surfactants) increased the surface diffusion length, whereas surfactants which were in substitutional sites (reactive surfactants) decreased it.

J.Massies, N.Grandjean: Physical Review B, 1993, 48[11], 8502-5