  An epitaxial heterojunction made of a p-type perovskite manganite
La0.8Sr0.2MnO3 film and an n-type strontium titanate SrTiO3:Nb substrate has
been fabricated by the pulsed laser deposition technique. The I - V
characteristics and photovoltaic properties are measured under a UV light
irradiation in a wide temperature range down to 10 K. It is found that the
junction works as an efficient UV photodiode with a large external quantum
efficiency of 28%. It is also demonstrated that the manganite film can be doped
with a certain amount of holes by the photcarrier injection. The maximum
surface hole density is estimated to b 3.0 X 10^13 cm^-2.
