Photoconductivity and photovoltage in oxygen deficient La_0.9Na_0.1MnO_3-δ/Si heterojunction

The photoinduced transportation with bias in the p-n junction composed of oxygen deficient La_0.9Na_0.1MnO_3-δ film and Si substrate under 473 nm laser irradiation is investigated. As laser intensity rises, the threshold voltage decreases significantly and even disappears in the temperature range from 30 to 300 K. A remarkable photoconductivity in both forward and backward directions is discovered. The ratio of photocurrent to dark current increases with the decrease of temperature, and the maximum value reaches 4778 in the backward direction by the excitation of 1.2 mW mm^-2 laser at 30 K. The maximum photovoltage abnormally occurs at intermediate temperature of 160 K, which may result from a competition between thermal carriers' effect and the delocalization of small polarons in La_0.9Na_0.1MnO_3-δ layer. These significant photoelectric effects make the La_0.9Na_0.1MnO_3-δ/Si junction promising for the design of photosensors with high performance.