Effect of Two-Dimensionality on Step Bunching on a Si(001) Vicinal Face

Abstract

We study the effect of two-dimensionality on step bunching on a Si(001) vicinal face heated by direct electric current. When the anisotropy of the diffusion coefficient changes alternately on consecutive terraces like a Si(001) vicinal face, bunching occurs with the drift of adatoms.If the wandering fluctuation of step bunches is neglected as in the one-dimensional model, the bunching with step-down drift is faster than that with step-up drift in contradiction with experiment (Latyshev et al., Appl. Surf. Sci. 130-132, 139 (1998)). In a two-dimensional model with a wide system width, the step bunches wander heavily with step-up drift, and the recombination of neighboring bunches occur more frequently than those with step-down drift.The bunching with step-up drift is accelerated and can be faster than that with step-down drift. KEYWORDS:Step bunching, Step Wandering, Si (001) The Si(001) surface is reconstructed by the dimerization of surface atoms. When its vicinal face is tilted in the 110 direction, the terraces with dimer rows parallel to the steps, T A , and those with dimer rows perpendicular to the steps, T B , appear alternately. Since the surface diffusion along the dimer rows is faster than that across the dimer rows, the anisotropy of the surface diffusion changes alternately on consecutive terraces.On the vicinal face, two types of step instabilities, step wandering 1 and step bunching, [1][2][3] occur when a specimen is heated by direct electric current. The step wandering occurs with step-up current in a region of relatively large inclination (the tilting angle is 0.08Due to the step wandering, grooves perpendicular to the steps appear on the vicinal face. The step bunching 1-3 occurs irrespective of the current direction in the region of small inclination (θ ≤ 0.08 • ). The types of dominant terraces, which separate step bunches, are T B with stepdown current and T A with step-up current. The size of the bunches increases with time as t 1/2 , 3 which is independent of the drift direction. The growth rate of the bunches with stepdown current seems slightly slower than that with step-up current. 3The step instabilities are caused by drift of adatoms induced by the current. By taking account of the alternation of the anisotropic surface diffusion, the step instabilities are *

Motion of step pairs during drift-induced step bunching on a Si(001) vicinal face

“…The step bunching occurs irrespective of the drift direction, which agrees with the experiments [1][2][3]. The form of bunches changes with the drift direction [11]: the bunches with step-up drift wander and frequently combine with each other (Fig. 1(b)), while the bunches with stepdown drift are straight and seldom combine ( Fig.…”

“…1(a)). The recombination of bunches neglected in the one-dimensional model [8,9] accelerates the step bunching, and the bunches with step-up drift grow faster than those with step-down drift [11]. In both cases, step pairs cross the large terraces.…”

“…The cause of the bunching is considered to be drift of adatoms induced by the current [4][5][6][7][8][9][10][11]. The drift and the current are in the same direction [12,13].…”

“…In a one-dimensional model [5,6,8,9], contrary to the experiment [2], the bunches with step-up drift grow slower than those with step-down drift. In a twodimensional model [7,11], the bunches wander heavily and recombine with neighboring bunches with step-up drift. The growth rate is accelerated by the recombination and becomes faster than that with step-down drift as in the experiment [2].…”

Effect of step permeability on step instabilities due to alternation of kinetic coefficients on a growing vicinal face

“…The cause of the instabilities is considered to be a e-mail: sato@cs.s.kanazawa-u.ac.jp the drift of adatoms induced by the current [7][8][9][10][11][12][13][14]. If we take account of the alternation of the anisotropic surface diffusion, the step wandering occurs with step-up drift [12], and the bunching occurs irrespective of the drift direction [7][8][9][10][11][12][13][14].…”