Structure of the Al-GaAs(110) interface from an energy-minimization approach

The structure of the Al-GaAs(110) interface at the initial stages of Al deposition has been studied. In this system, the adatom-substrate and the adatom-adatom interactions are not necessarily weak, and the interface region may be strongly perturbed. The pseudopotential-energy minimization method is ideally suited for determining the stable structure of such systems involving significant energy change, and this method is successfully applied to the Al-GaAs system in the present study. By the calculation of the chemisorption energy of the Al atom at different sites on the entire GaAs surface, an energy contour map is obtained for the first time. Favorable channels of migration of Al atoms on this map are identified, which suggests preferential surface diffusion along the Ga—As bonding chain direction. The calculated surface hopping diffusion is sufficiently high even at room temperature so that Al atoms frequently encounter and interact with other Al atoms to form Al clusters. The Al clusters are found to have lower free energy than chemisorbed Al atoms. Al atoms eventually replace substrate Ga atoms and form Al—As bonds in the interface region to minimize the energy of the system.