Barrier Lowering and Field Penetration at Metal-Dielectric Interfaces

We report here photoemission measurements on -SiO_2-Al structures in which the metal-SiO_2 energy has been determined as a function the electric field strength E in the dielectric. The barrier lowering is the sum of two terms: ) the Schottky term, proportional to E^(1/2) and b) term due to the penetration of the electric field the metal electrode, proportional to E. The results are in good agreement with model, where the Schottky effect involves the value of the dielectric constant of the oxide the Thomas-Fermi screening distance in the is 1 Å. To our knowledge this represents the unambiguous quantitative determination of either effect in a polar dielectric, although the effect alone has been observed in silicon.