STRUCTURE OF LOW-COVERAGE PHASES OF AL, GA, AND IN ON SI(100)

The atomic structures of the low-coverage 2 x 2 phases of Al, Ga, and In on Si(100) were determined on the basis of first-principles total-energy calculations and angle-resolved photoemission experiments. The proposed structure consists of rows of ad-dimers, with the ad-dimers oriented parallel to the underlying Si dimers. Angle-resolved photoemission experiments performed for Si(100)2 x 2: In are in good agreement with the calculated surface-state dispersions for the parallel ad-dimer model. The existence of lower coverage 3 x 2 and 5 x 2 phases results from repulsive interactions between neighboring rows of ad-dimers.