Probing electronic defect states in manganite/SrTiO3 heterostructures by surface photovoltage spectroscopy

The energetic distribution of electronic defect states in oxide heterostructures made of ultrathin lanthanum manganite (La0.7Ca0.3MnO3, La0.7Ce0.3MnO3) films on SrTiO3 substrates is investigated by surface photovoltage (SPV) spectroscopy. Within a comparative evaluation of the SPV spectra of both the film/substrate structures and pure substrates at different temperatures we were able to elaborate a map of defect states across the SrTiO3-bandgap and we find that the defect state distribution is mainly affected by the substrate, i.e., no specific film-induced defect states were detected. Possible origins of the defect states are discussed within the framework of a semiconductor band scheme, taking into account complementary photoconductivity and SPV transient data.