A theoretical study of Al overlayers on Si(111)

The surface system Si(111) with chemisorbed monolayers of Al is investigated theoretically. Within the self-consistent pseudopotential scheme several different structural models for chemisorption are studied and spectroscopic results are compared to recent experimental photoemission and electron energy loss data obtained on similar systems. It is found that chemical bonds between substrate and metal are formed yielding states in the semiconductor gap which stabilize the Fermi level. From the detailed analysis of several strong spectroscopic features it follows that the interface may structurally be modelled by Al atoms sitting in threefold coordinated positions either above the Si(111) surface or replacing the outermost silicon layer, (i.e., Lander’s substitutional model).