The atomic structures of the low-coverage 2×2 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)2×2:ln are in good agreement with the calculated surface-state dispersions for the parallel ad-dimer model. The existence of lower coverage 3×2 and 5×2 phases results from repulsive interactions between neighboring rows of ad-dimers.

• Received 22 August 1991

DOI:https://doi.org/10.1103/PhysRevB.44.13799