  The heterostructure consisting of the Mott insulator LaVO$_3$ and the band
insulator SrTiO$_3$ is considered a promising candidate for future photovoltaic
applications. Not only does the (direct) excitation gap of LaVO$_3$ match well
the solar spectrum, but its correlated nature and predicted built-in potential,
owing to the non-polar/polar interface when integrated with SrTiO$_3$, also
offer remarkable advantages over conventional solar cells. However,
experimental data beyond the observation of a thickness-dependent
metal-insulator transition is scarce and a profound, microscopic understanding
of the electronic properties is still lacking. By means of soft and hard X-ray
photoemission spectroscopy as well as resistivity and Hall effect measurements
we study the electrical properties, band bending, and band alignment of
LaVO$_3$/SrTiO$_3$ heterostructures. We find a critical LaVO$_3$ thickness of
five unit cells, confinement of the conducting electrons to exclusively Ti 3$d$
states at the interface, and a potential gradient in the film. From these
findings we conclude on electronic reconstruction as the driving mechanism for
the formation of the metallic interface in LaVO$_3$/SrTiO$_3$.
