Effect of evaporation on step bunching induced by impurities

In this paper, we study the effect of the evaporation of adatoms and impurities on the step bunching induced by impurity. Keeping the ratio of the impingement rate of impurities F_{imp} to that of atoms F constant, we carry out Monte Carlo simulation. In the system with the evaporation of impurities, the growth rate of vicinal face R is proportional to F. This relation is the same as that without the evaporation of impurities. When F is small, the vicinal face is unstable. Compared with the system without the evaporation of impurities, the effect of impurities is weakened. In our simulation, step pairing occurs but large bunches are not formed. When we take account of the evaporation of both impurities and adatoms, the vicinal face grows when F is larger than the equilibrium value F_{eq}. R is not proportional to (F-F_{eq}) and large bunches are formed when F is small. In this paper, we also show how the impurity density on surface σ_{imp} and that incorporated in solid ρ_{imp} are related to the formation of step bunches.