  Internal photoemission spectroscopy was used to determine the Schottky
barrier height in rectifying SrRuO3/Nb-doped SrTiO3 junctions for 0.01 wt % and
0.5 wt % Nb concentrations. Good agreement was obtained with the barrier height
deduced from capacitance-voltage measurements, provided that a model of the
nonlinear permittivity of SrTiO3 was incorporated in extrapolating the built-in
potential, particularly for high Nb concentrations. Given the generic
polarizability of perovskites under internal/external electric fields, internal
photoemission provides a valuable independent probe of the interface electronic
structure.
