AVS 46th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS2+EM-TuA

Paper SS2+EM-TuA4
The Structure of Steps on Hydrogen-Passivated Si Surfaces

Tuesday, October 26, 1999, 3:00 pm, Room 6C

Session: Semiconductor Surface Chemistry
Presenter: A. Laracuente, Naval Research Laboratory
Authors: A. Laracuente, Naval Research Laboratory
L.J. Whitman, Naval Research Laboratory
Correspondent: Click to Email
Steps play a critical role during epitaxy, so knowing their structure is crucially important to understanding how films grow. There has been a considerable effort to determine the step structure on Si surfaces oriented near (001).@footnote 1@ On surfaces tilted toward (111), there are four distinct step configurations, single- and double-layer A-type and B-type steps, commonly denoted as S@sub A@, S@sub B@, D@sub A@, and D@sub B@. B-type steps are almost always "rebonded," with two extra atoms per unit cell at the step edge. The extra atoms halve the dangling bond density along each step and thereby make this structure energetically preferred over a non-rebonded configuration. On surfaces tilted more than 3°, only rebonded D@sub B@ steps occur. Because most industrial Si film growth happens in the presence of hydrogen, an accurate picture of such growth requires an understanding of how H affects the Si step structure and dynamics. It was recently predicted theoretically that non-rebonded steps should be energetically more favorable on H-terminated Si.@footnote 2@ We have now verified this prediction experimentally on a range of surfaces oriented from (001) to (114). We find that S@sub B@ steps "unrebond" after H-passivation, as predicted, completely altering the step energetics. Similarly, H passivation splits a large fraction of D@sub B@ steps into S@sub A@+S@sub B@ step combinations. These changes in step structure have a dramatic effect on the step dynamics and the resulting surface morphology, generally leading to much rougher surfaces. We will discuss how these changes can explain a variety of previous observations about the effects of H on Si film growth. @FootnoteText@ @footnote 1@ A. A. Baski, S. C. Erwin, and L. J. Whitman, Surf. Sci. 392, 69 (1997). @footnote 2@ S. Jeong and A. Oshiyama, Phys. Rev. Lett. 81, 5366 (1998).