The initial Ge growth on the GaAs(001) surface was studied. It was found that the initial Ge growth promoted the site exchange between Ge and As atoms, resulting in the formation of surface Ga-As dimers with (1 x 2) periodicity. The proposed structure model was found to be energetically favourable by first-principles calculations, and explains well the experimental data from scanning tunnelling microscopy and reflection high-energy electron diffraction.

Ge-Induced (1 x 2) Surface Reconstruction on GaAs(001) - a Precursor to As Segregation. A.Ohtake, J.Nara, T.Yasuda, N.Miyata: Physical Review B, 2008, 77[19], 195309 (5pp)