PROBING THE CAF2 DENSITY-OF-STATES AT AU CAF2/N-SI(111) INTERFACES WITH PHOTOELECTRON-SPECTROSCOPY AND BALLISTIC-ELECTRON-EMISSION MICROSCOPY/

The electronic properties, chemistry, and spatial structure of Au/CaF2 /n-Si(111) metal-insulator-semiconductor (MIS) structures, with epitax ially grown CaF2 layers of a few monolayers (ML) thickness, have been studied by photoelectron spectroscopy, scanning-tunneling microscopy, and ballistic-electron emission microscopy. CaF2 films on Si are chara cterized by flat surfaces with defect lines about 500 angstrom apart, and band bending in Si reduces gradually with increasing CaF2 layer th ickness. Au grows on top of the CaF2 layer in the form of hexagonal te rraces. A Si segregation to the surface, as observed in case of the ba re Au/Si interface, is strongly reduced by the CaF2 intralayer. Ballis tic-electron emission microscopy shows a strong influence of the CaF2 density of states for electron transport through the intralayer. For a 4 ML thick CaF2 intralayer, the position of the CaF2 conduction-band minimum is derived from the onset of the collector current at 3.3 V Th e valence-band offset at the CaF2/Si interface is derived from the val ance-band edge observed in photoelectron spectroscopy.