Electronic, structural, and dynamical properties of the GaAs(110):Ge surface

We have investigated the structural, electronic, and vibrational properties of Ge overlayers on the GaAs(110) surface in the framework of the density-functional theory within the local-density approximation. By minimizing the total energy with the help of the Hellmann-Feynman forces, we have found two different zero-force configurations for the GaAs(110) surface covered with one monolayer (ML) Ge as well as for two ML's Ge on GaAs(110). For both coverages the atomic equilibrium positions and most of the electronic surface states corresponding to the optimized structure with the lower energy minimum are very similar to those of the clean GaAs(110) surface. A thermodynamical analysis indicates an instability towards cluster formation. In the case of one ML Ge on GaAs(110) we have calculated the phonon-dispersion curves along high-symmetry lines in the surface Brillouin zone using first-order density-functional perturbation theory without any adjustable parameters. As well as the electronic properties, the features of the phonon spectrum mostly resemble those of the clean surface. Beside the appearance of an additional surface acoustic mode the main effect of Ge adsorption is a slight down-shift of the phonon frequencies. The dynamical analysis of the GaAs(110)-(1 x 1):Ge surface (1 ML) at T = 0 shows no instability towards reconstructions with periodicity along the high symmetry directions <(Gamma)over bar> (X) over bar and <(Gamma)over bar> (X) over bar'.