DEFECTS IN THE RECONSTRUCTED (111) AND ( ) SURFACES OF InSb. H. Schulz, H. Vogler, H.L. Meyerheim, W. Moritz Institut für Kristallographie und Mineralogie, Universität München, Theresienstr. 41, 80333 München, Germany

The 3D-structures of the (111) and ( ) surfaces of InSb have been determined by grazing incidence x-ray diffraction using superstructure reflections up to high exit angles. Both surfaces exhibit a reconstruction. The In-terminated (111) surface shows a (2x2) reconstruction and the Sb-terminated ( ) surface has a (3x3) structure.

The (2x2) reconstruction is characterised by a In-vacancy and at rearrangement of the bonds of the surface atoms which can be explained, by rehybridisation and depolarisation [1]. Similar structures have been found on other III/V semiconductor surfaces. We present here a new 3-D x-ray structure analysis using 29 symmetrically independent in-plane reflections and 244 out-of-plane reflections from superstructure rods and truncation rods. The results clearly favour the model with statistically distributed Sb vacancies in addition to the In vacancies [2]. The density of the Sb vacancies is about 0.07 monolayers, i.e. in one of three or four (2x2) unit cells the In vacancy is occupied and an Sb is missing. The existence of Sb-vacancies is not expected on this surface from total energy calculations and also from the observation that by the defects the electron counting rule is violated. The existence of defects is discussed and compared to the (3x3) reconstruction of the ( ) surface. In this surface 6 of the 9 dangling bonds in the (3x3) unit cell are saturated by rings of 6 atoms. The rings are statistically distributed and oriented. The results of the x-ray structure analysis agree well with STM images of the same surface [3].

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[2] A. Belzner, E. Ritter, and H. Schulz, Surf. Sci. 209, (1989) 379.

[3] J. Wever, H.L. Meyerheim, W. Moritz, V. Jahns,, D. Wolf, H. Schulz, L. Seehofer and R.L. Johnson, Surf. Sci Lett. 321 (1994) L225.