Subsurface Relaxation Research Articles

Calculation of atomic relaxation near the (111) 1 × 1 surface of covalent semiconductors: Tight‐binding Green's function approach

AbstractThe atomic relaxations near the (111) 1 × 1 covalent semiconductor (C, Si, and Ge) surfaces are calculated using a tight‐binding Green's function approach and compared with the results of LEED experiments as well as those of other theoretical calculations. The present calculation takes into account the repulsive interaction energies between adjacent atomic sites and uses a total energy minimization procedure. It is shown that the change in the topmost interlayer spacing δ0 depends strongly on the material and subsurface relaxation is unimportant. The value of δ0 increases rapidly as going C(≈︁ 1%) → Si(≈︁ 5%) → Ge(≈︁ 13%). Simple physical interpretation for this behaviour is also given.

(110) surface atomic structures of covalent and ionic semiconductors

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\ifmmode^\circ\else\textdegree\fi{} in Si to 25.6\ifmmode^\circ\else\textdegree\fi{} 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 (\ensuremath{\approx} 0.02 eV) contribution to the lowering of the total energy.

Energy-Minimization Approach to the Atomic Geometry of Semiconductor Surfaces

The (110) surface atomic geometries of GaAs and ZnSe and of 2 \ifmmode\times\else\texttimes\fi{} 1 reconstructed (111) surface of Si are calculated by minimizing the total energy of the electron-ion system. The corresponding reductions in total energy between the relaxed and unrelaxed surfaces are calculated to be - 0.51, - 0.30, and - 0.37 eV per surface atom, respectively. Subsurface relaxations are generally found to make a very small (\ensuremath{\le} 0.02 eV) contribution to the reduction in total energy.