Studies of the Si(111) surface with various Al overlayers

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Abstract
The electronic structure of the Si(111) surface with Al overlayers has been investigated by the self-consistent pseudopotential method for three different Al chemisorption sites. The geometries are a onefold coordinated covalent site, and two other geometries which correspond to threefold coordinated ionic sites with different Al-Si bond lengths. The electronic energy bands, local densities of states, and charge distributions for some surface states are presented in detail. The results together with those of a previous calculation based on the Lander substitutional geometry are compared to recent photoemission and electron-energy-loss experiments on Si(111) with adsorbed Al overlayers of variable thickness. The study yields structural information on the formation of covalent metal-semiconductor bonds which stabilize the Fermi level and which are believed to be essential in the formation of Schottky barriers.