Growth of permeable step bunches formed by drift of adatoms

We study bunching of permeable steps induced by drift of adatoms. In contra st to impermeable steps, bunching may occur with step-up drift. When diffus ion length is short, terrace width between the bunches increases as L propo rtional to t(beta) with beta approximate to 1/2 through collision and coale scence. After the power law growth, the system reaches a steady state, wher e an array of similar bunches coexists with a few single steps on large ter races. If the diffusion length is long, the exponent beta increases up to o ne. (C) 2001 Elsevier Science B,V. All rights reserved.