The Two-Dimensional Nucleation Rate for a Homopolar Crystal Containing Microscopic Defects

Abstract

The classical kinetic treatment of layer growth of crystal faces involves the assumption that the two-dimensional nucleation is the rate-limiting step, which implies extremely low values for growth rates at low and medium super saturations. The calculated growth rates are less by many orders of magnitude than the observed ones. The discovery of the dislocation growth mechanism would have appeared to have resolved this conflict between theory and experiment, and it would seem that the growth of the faces of the equilibrium form (G faces) would occur by the two-dimensional mechanism only at high supersaturations. However, methods have been developed for making almost dislocation-free crystals, and studies on the growth of these have shown that G faces in such crystals can grow at fairly high rates at low supersaturations. Under certain conditions, nucleation is so fast that the growth is limited not by nucleation but by bulk diffusion or by the deposition kinetics of the material during reactions in the vapor state.