Geometric structure and optical properties of the $\mathrm{Ga}\mathrm{As}\left(001\right)\text{−}c(4\times 4)$ surface

We consider the electronic structure and optical properties for several geometries of the $\mathrm{Ga}\mathrm{As}\left(001\right)\text{−}c(4\times 4)$ surface using first-principles calculations. We find strong evidence that the best agreement with photoemission and reflectance anisotropy spectroscopy experiments carried out on surfaces prepared under ${\mathrm{As}}_4$ flux is obtained for a structure containing three $\mathrm{Ga}\text{–}\mathrm{As}$ dimers per unit cell. The standard $\mathrm{As}\text{–}\mathrm{As}$ dimer model yields similar, but distinguishable results, while an asymmetric dimer model is found to yield completely incompatible surface spectra.

Figure 1

Schematic representations of the $\mathrm{Ga}\mathrm{As}\left(001\right)(4\times 4)$ surface: (a) symmetric dimer model; (b) mixed dimer model; (c) asymmetric dimer model. In (d) the $c(4\times 4)$ surface Brillouin zone is shown referred to the primitive $(1\times 1)$, $(2\times 2)$, and $(4\times 4)$ zones.

Figure 2

DFT-LDA band structure of the $\mathrm{Ga}\mathrm{As}\left(001\right)\text{−}c(4\times 4)$ surface, for the symmetric and mixed dimer models. (Large) dots indicate states (strongly) localized at the surface. The shaded region marks the (computed) projected bulk band structure.

Figure 3

RAS spectra of the $\mathrm{Ga}\mathrm{As}\left(001\right)-c(4\times 4)$ surface. (a) Lines: experimental data from Ohtake et al. (Ref. 12); points: data of Ref. 24, for a surface prepared with ${\mathrm{As}}_4$ flux. (b) Theoretical results. (c) Spectra from topmost layers only.