  Oxide heterojunctions made of p-type L0.8Sr0.2MnO3 (LSMO) and niobium-doped
n-type SrTiO3 (STO:Nb) have been fabricated by the pulsed laser deposition
(PLD) technique and are characterized under UV light irradiation by measuring
the current-voltage, photovoltaic properties and the junction capacitance. It
is shown that the heterojunctions work as an efficient UV photodiode, in which
photogenerated holes in the STO:Nb substrate are injected to the LSMO film. The
maximum surface hole density Q/e and external quantum efficiency gamma are
estimated to be 8.3x1012 cm-2 and 11 % at room temperature, respectively. They
are improved significantly in a p-i-n junction of LSMO/STO/STO:Nb, where Q/e
and gamma are 3.0x1013 cm-2 and 27 %, respectively.
