Rectifying and ultraviolet photovoltage characteristics of La_0.9Na_0.1MnO₃/SrTiO₃-Nb heterostructures

Rectifying and photovoltaic properties of a La_0.9Na_0.1MnO₃/SrTiO₃-Nb (LNMO/STON) heterostructure have been experimentally studied. The heterostructure exhibited abnormal rectifying behavior, i.e., the threshold voltage increased with the increasing temperature in a wide range of 40 to 300 K. A temperature dependent photovoltaic response was observed when the heterostructure was excited by a 248 nm ultraviolet laser with a duration of 30 ns. The increased photovoltage was found to result from two distinctive carrier accumulation processes (from the edge of the depletion layer to the surface electrodes in LNMO and STON). The two characteristic times τ₁ and τ₂ were determined by the hole and electron mobility in the LNMO and STON. The significant temperature-dependent τ₁ resulted from different transportation mechanisms in the metallic and insulator states of LNMO. The very short τ₂ was related to the high electron mobility in STON. The lifetime of the nonequilibrium carrier was determined to be ∼10 ms by the analysis on the decaying process, indicating a relatively longer charge diffusion length as compared with that in other doped manganite p-n junctions.