Preparation And Characteristic Research Of Doped Perovskite Cobaltites Heterojunction

In this paper,(La_1-xPr_x)_0.7Sr0.3CoO3?x=0,0.2,0.4,0.6,0.8? and La_0.82Sr_0.18Co_1-xCr_xO₃?x=0,0.2,0.4,0.6,0.8,1.0? series heterojunctions were fabricated by pulsed laser deposition?PLD? on n-type 0.7wt%Nb-SrTiO3?100? substrates. Structure, surface morphology, transport properties and photovoltaic characteristics were investigated by X-ray diffraction?XRD?, Atomic force microscope?AFM?, low temperature test system and optoelectronic measuring system, respectively. The main conclusions in this paper are as follows:1. The tests by XRD and AFM show that the samples have good epitaxial growth characteristics and the films grew preferentially along the crystal orientation of substrate; the surface particles of all samples are compact and uniform and fluctuation degree is very small, which indicate the good quality of the samples we have prepared. Measured by spectroscopic ellipsometer, the thickness of all the heterojunction films are in the range of 90-110 nm.2. The lattice structure of material changes with doping of Pr ions in(La_1-xPr_x)_0.7Sr_0.3CoO₃/Nb-SrTiO₃ series heterojunctions, which show different transport properties due to different lattice mismatch degree between films and substrates. With the increase of temperature, the junction barrier decrease, the thickness of depletion layer narrow and the rectification property of the heterojunction weaken.3. Under the irradiation of laser, continuous photovoltage was tested in the doped(La_1-xPr_x)_0.7Sr_0.3CoO₃/Nb-SrTiO₃ series heterojunction samples. The value of photovoltage under 473 nm laser is bigger than which under 532 nm laser. As the temperature rises, the maximum photoproduction voltage of x=0.8 heterojunction is reduced. By fitting the rising and falling edge of photovoltage, we found out that the lifetime of nonequilibrium charge carriers was in a large magnitude and decreased with increasing temperature.4. In La_0.82Sr_0.18Co_1-xCr_xO₃/Nb-SrTiO3 series heterojunctions, low doped heterojunctions possess good rectification property, and the interface leakage mechanism of higher doped is mainly ohmic conduction, which caused by electron transition between Co and Cr ions increasing the carrier concentration of the materials.5. Under the irradiation of laser, photovoltaic effect were observed in the samples of x=0 and x=0.4 and the value of photovoltage under 473 nm laser is bigger than under 532 nm laser. As the temperature rises, the maximum photoproduction voltage of x=0 heterojunction increased at first and then decreased. Rise-time constant of lifetime of nonequilibrium charge carriers decreased with increasing temperature and had great value at low temperature, which is useful for improving the performance of photovoltaic devices.