Ballistic electron emission microscopy measurements of epitaxially grown Pt/CaF2/Si(111) structures

The electronic transport properties and surface morphology of ultrathin Pt/CaF2/Si(111) metal-insulator-semiconductor structures have been characterized in-situ by ballistic electron emission microscopy (BEEM) and scanning tunneling microscopy (STM). Platinum thicknesses from 2–53Åand CaF2 thicknesses of 5 and 15Åhave been characterized. The STM images of the Pt/CaF2/Si(111) structures show the atomic steps of the underlying CaF2 morphology, as well as the formation of Pt nodules. The BEEM spectra from the thicker Pt coverages show an onset near the conduction band minimum (CBM) of the CaF2. The BEEM spectra from the thinner Pt coverages show an additional peak near 2 eV, which has not been observed in previous studies of metal/CaF2/Si(111) structures. This extra peak has been attributed to quantum mechanical resonant tunneling through the ultrathin MIS structure.