(110) surface atomic structures of covalent and ionic semiconductors

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Abstract
A total-energy-minimization approach is applied to the determination of the (110) surface atomic geometries of Si, Ge, GaAs, InP, InSb, ZnSe, and ZnTe. The accuracy of the model employed in the energy minimization was tested by comparing calculated values of bulk elastic coefficients and phonon frequencies to experimental data. Generally good agreement between the calculated and experimental results were obtained. The relative displacements of nearest-neighbor surface atoms, when scaled for differences in lattice constants, are found to be very similar for all the semiconductors studied. The displacements of individual atoms from unrelaxed bulk terminated positions are, however, appreciably different and ionicity dependent. The bond rotation or tilt angle at the surface which provides a partial characterization of surface relaxation is nearly constant varying only from 30° in Si to 25.6° in ZnSe. The reduction in total energy resulting from surface relaxation decreases from approximately -0.55 eV (per surface atom) in Si to -0.30 eV in ZnSe and ZnTe. Subsurface relaxations are generally found to make a very small (≈ 0.02 eV) contribution to the lowering of the total energy.