  A generally applicable model is presented to describe the potential barrier
shape in ultra small Schottky diodes. It is shown that for diodes smaller than
a characteristic length $l_c$ (associated with the semiconductor doping level)
the conventional description no longer holds. For such small diodes the
Schottky barrier thickness decreases with decreasing diode size. As a
consequence, the resistance of the diode is strongly reduced, due to enhanced
tunneling. Without the necessity of assuming a reduced (non-bulk) Schottky
barrier height, this effect provides an explanation for several experimental
observations of enhanced conduction in small Schottky diodes.
