CRITICAL-TEMPERATURE FOR MOUND FORMATION IN MOLECULAR-BEAM EPITAXY

The results of an analytic calculation of the surface current and sele cted mound angle as a function of the Ehrlich-Schwoebel step barrier E (B) and substrate temperature T are presented for a model of epitaxial growth on bcc(100) and fcc(100) surfaces. Depending on the sign of E( B) and the magnitude of the prefactor for diffusion over a step, vario us scenarios are possible, including the existence of a critical tempe rature T-c for mound formation above which (for a positive step barrie r) or below which (for a negative step barrier) quasi-layer-by-layer g rowth will be observed. For the case of Fe/Fe(100) deposition our calc ulation implies an upper bound for T-c which is consistent with experi ment. The weak parameter dependence of our estimates for the mound ang le confirms and explains the good agreement found in previous estimate s assuming different values of the step barrier. We also clarify the t ransition to layer-by-layer growth at low and high temperature includi ng the effect of a finite diffusion length on reentrant behavior at lo w temperature.