No, by thermodinamical asprcts this effects takes place in the surface. One of the reasons why you have to optimize substrate temperature. Being its influence also in diffudion lenght searching for a proper place in the formind 2d layer. Hope is clear. A comprehensive analysis, for instance J. Y. Tsao "materials fundamentals of MBE" Ac. Press and MA. Hermann, H. Sitter "Moleecular Beam Epitaxi+y". Springer series in materials science.