Electrode size dependent IV characteristics and photovoltaic effect in the oxide pn junctions Pr_0.7Ca_0.3MnO₃Nb: SrTiO₃ and La_0.7Ca_0.3MnO₃Nb : SrTiO₃

Hole doped manganites Pr_0.7Ca_0.3MnO₃ (PCMO) and La_0.7Ca_0.3MnO₃(LCMO) films have been epitaxially grown on the electron doped Nb:SrTiO₃ (NSTO) substrates by pulsed laser deposition. The rectifying characteristic observed in the currentvoltage (IV) measurement was better in the PCMO/NSTO junction than in the LCMO/NSTO one. A resistance switching behavior in the IV curves was observed with decrease of the Au electrode size and it was thought to be due to Schottky barrier at the NSTO/Au contact. The temperature dependence of the threshold voltage, which shows a dramatic increase of the current, varied slightly around the metalinsulator transition temperature of the LCMO. These results suggest that the measurement of IV characteristics in these pn junctions can be largely affected by the electrode size and the temperature. The photocurrent and the photovoltage across the pn junctions in zero external bias were quickly switched by on/off of visible or UV light. This result suggests that the photo-carriers can be generated in both the p-type and the n-type layers.