Series resistance effects in La0.5Ca0.5MnO3/SrTiO3:Nb(0 0 1) heterojunctions

The effects of series resistance in heterojunctions composed of La0.5Ca0.5MnO3 (LCMO) and Nb:SrTiO3 with 0.05 wt.% and 0.7 wt.% of Nb doping (0.05NbSTO and 0.7NbSTO) have been investigated in detail using current–voltage curves with and without light illumination. Two linear plots, namely, dV/dlnJ versus J and H(J)[≡V-(nk B T/q)ln(J/A**T 2)] versus J, have been used to extract the series resistance. These two plots give very close values. The extracted series resistance exhibits a monotonous increase with decreasing temperatures, which could explain the observed anomalous temperature dependence of short circuit current in LCMO/0.7NbSTO.