Comparison of the atomic geometries of GaSb(110) and ZnTe(110): Failure of ionicity-structure correlations

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Abstract
The atomic geometries of the (110) surfaces of GaSb and ZnTe are determined by comparing calculated elastic low energy electron diffraction (ELEED) intensities with those measured at T=125 K. The quality of the model description of the observed intensities is measured by the x ray R factor Rx. Using the minimization of Rx as the structure determination criterion, the atomic geometries of these two surfaces are shown to be very similar, in fact, nearly identical to within the uncertainties inherent in the analysis. GaSb(110) is reconstructed via a bond-length conserving rotation in its uppermost atomic layer characterized by ω1=30±2°, and the Sb relaxed outward from the substrate. ZnTe(110) exhibits an analogous bond-length conserving rotation of ω1=28±2° in its uppermost layer. In addition, however, this layer is relaxed by 0.05±0.05 Å toward the substrate, and the second layer exhibits a counter relaxation of the Zn outward by 0.025±0.05 Å and the Te inward by 0.025±0.05 Å. The spectroscopic ionicity of GaSb is fi=0.26, whereas the difference in Pauling electronegativities of Sb and Ga is ΔX=0.3. For ZnTe the values are fi=0.55 and ΔX=0.5. The absence of second-layer relaxations for GaSb(110) reveals that such relaxations are not characteristic of all highly covalent compound semiconductors (i.e., fi<0.5, ΔX0.5. Thus, this characteristic feature of the surface atomic geometries of the (110) surfaces of zinc-blende-structure compound semiconductors does not correlate simply with either the spectroscopic or Pauling ionicities.

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