Electronic and optical properties of GaAs(001) (2×4) and (4×2) surfaces

We present theoretical studies of the electronic and optical properties of GaAs(001) surfaces with different reconstructions at 0 K and at typical growth temperatures near 850 K. Ga-rich (4×2) missing-dimer surface and three different phases (α, β, and γ) of the As-rich (2×4) surface are considered. A nearest-neighbor tight-binding model with six orbitals (${\mathit{sp}}^3$ ${\mathit{d}}^{2)}$ per atom is employed. Total-energy calculations are performed to determine the surface geometry for each reconstruction considered. The surface local density of states and surface dielectric functions of these surfaces are calculated. The difference between dielectric functions with [110] and [1¯10] polarization for these surfaces is analyzed and compared to available data.