AVS 45th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM9
The Structure of Ge Surfaces from (001) to (111)

Tuesday, November 3, 1998, 11:00 am, Room 308

Session: Semiconductor Surface Structure
Presenter: A. Laracuente, Naval Research Laboratory
Authors: A. Laracuente, Naval Research Laboratory
S.C. Erwin, Naval Research Laboratory
L.J. Whitman, Naval Research Laboratory
Correspondent: Click to Email
We are studying the structure of Ge surfaces oriented between (001) and (111) using STM and first-principles electronic structure calculations (LDA). Similar to Si,@footnote 1@ Ge surfaces oriented within ~12° of (001) and (111) consist of low-index terraces and steps. Between this range, it appears that only (113) and ~(559) are planar surfaces on Ge, in contrast to Si where (114), (113), and (5 5 12) are planar. Because (113) is the only planar high-index surface common to Si and Ge in this range, its structure is of particular interest. At room temperature, Si(113) has a (3x2) reconstruction that incorporates a highly unusual six-fold-coordinated surface interstitial. The "self-interstitials" occur within every other tetramer (a dimer plus nonrebonded double-layer step), making the otherwise (3x1) surface (3x2). At room temperature the Ge(113) surface consists of an equilibrium mixture of (3x1) domains (~80%) and Si-like (3x2) domains (~20%). In contrast to previously reports, we find that the (3x1) domains have the same structure as Si(113)-(3x2), with the exception that every tetramer includes an interstitial. Extensive LDA calculations confirm that the "self-interstitials" dramatically lower the surface energy on Ge(113). Whereas on Si the (3x1) structure is 2 meV/ Å@super 2@ higher in surface energy than the (3x2), it is approximately degenerate on Ge (in agreement with experiment). Furthermore, calculations of the stability of interstitials at various sub-surface sites indicate that they do not migrate to the surface from the bulk, as previously suggested, but rather originate from surface adatoms (perhaps in a lattice gas). @FootnoteText@ @footnote 1@Baski, Erwin, and Whitman, Surf. Sci. 392, 69 (1997).