Bearing the Si(1 1 1) vicinal face in mind, we study the effect of impingement and evaporation on drift-induced step instabilities. On a Si(1 1 1) face, transition between 1 x 1 structure and 7 x 7 structure occurs at 860 degrees C. On the vicinal face near the transition temperature, the two structures coexist: the 1 x 1 structure is at the lower side of step and the 7 x 7 structure is at the upper side. On the 1 x 1 structure, the diffusion coefficient is larger than that on the 7 x 7 structure. When the difference in the diffusion coefficients is taken into account, step bunching occurs with drift of adatoms. In a conserved system with fast drift, separation and coalescence of steps occur repeatedly, and the bunches grow gradually. The motion of bunches changes when the impingement or evaporation is present. With the impingement, the separation of steps is suppressed and the bunches grow via coalescence of small ones with step-down drift, while the separation is more frequent than that in conserved system with step-up drift. With the evaporation, the relation is the opposite. (C) 2007 Elsevier B.V. All rights reserved.