EXPERIMENTS WITH EXTRINSIC SI(111) SURFACES - CS ADSORPTION AT ROOM-TEMPERATURE ON SI(111) TERMINATED WITH HYDROGEN AND OXYGEN

The characteristic intrinsic properties of silicon surfaces are strong ly related to the dangling bonds, and their presence again are due to the different possible reconstructions. It is possible to create surfa ces on which the dangling bands are removed or changed by adsorption o f gas atoms or metal atoms. Such surfaces may exhibit new, tailorable properties, making them interesting for device applications. In this r eport, the properties of hydrogen and oxygen terminated n-type Si(111) surfaces are compared with respect to Cs adsorption, and seen against those of the Si(111) 7 x 7 surface. The techniques include core level and alence band photoemission with synchrotron radiation at the Aarhu s storage ring spectroscopic optical second harmonic generation and LE ED. It is found that the hydrogen terminated (1 x 1) surface has pract ically no free dangling bonds and is unpinned. As a result the positio n of the band edge is strongly lowered with Cs adsorption. This surfac e is stable against Ca adsorption and shows a highly enhanced electron emission upon radiation with photons as a result of the loweroed work function. The (monolayer) oxygen terminated surface is electronically stable and shows a pinning of the surface potential resisting the move ment of the band edge with adsorption of Cs, despite a reaction betwee n Cs and oxygen. For the clean surface direct interactions between Cs and Si surface atoms create new interface states at the Fermi level. A number of less significant differences between these surfaces are als o pointed out.