Controlling Au/n-GaAs junctions by partial molecular monolayers

metal/semiconductor junctions with a discontinuous monolayer of polar molecules at the metal/semiconductor
interface. The effective barrier height of those junctions, which have small pinholes, embedded in a
molecular layer, which introduces a negative {positive} dipole (i.e., a dipole whose negative {positive}
pole is the one that is closest to the semiconductor surface) on an n-type {p-type} semiconductor, is often
"tunable" by the magnitude and density of the dipoles. If the lateral dimensions of a molecule-free pinhole
at the interface exceed the semiconductor depletion width, carrier transport is not influenced by the molecular
layer and the "effective" barrier height is the nominal metal/semiconductor barrier height. If the molecular
layer introduces a positive {negative} dipole on an n-type {p-type} semiconductor, enhanced field
emission at edges of small pinholes might lead to a leakage- and/or an edge-current component resulting
in an effective barrier height lower than the nominal one. We support these conclusions by direct measurements
of the nm-scale electronic behaviour of a Au/n-GaAs diode with a discontinuous monolayer of
dicarboxylic acids at the interface, using Ballistic Electron Emission Microscopy (BEEM).