The surface structure of aluminum overlayers on cleaved p-type GaAs (110) is studied by scanning tunneling microscopy (STM) in ultrahigh vacuum. About three monolayers of aluminum were deposited on the surfaces at room temperature. We observed that aluminum atoms form clusters, and found that one cluster, consisting of about 200 atoms, has nonmetallic characteristics with a band gap of 1 eV. We also observed adsorbed atoms located over Ga sites in STM images of both occupied and unoccupied states. Their corrugation amplitudes are about 1 Å above the GaAs surface.

• Received 19 April 1991

DOI:https://doi.org/10.1103/PhysRevB.44.3187