Epitaxial Growth And Electrical Properties Of La_0.9Sr_0.1MnO₃ Thin Films By Pulsed Laser Deposition

Sr doped lanthanum manganites La_1-xSr_xMnO₃ thin films are widely used in the production of various magnetic sensor,and magnetic recording microelectronic devices,fuel cell cathode,thermal sensor,intelligent heat control device because of the abundant electrical,magnetic and thermal properties.The researches are mainly focus on the doping amount of Sr in the recent work.However,the research about orientation of the substrate and lattice mismatch between substrates and the films is very few which will affect anisotropy of thin film growth and lattice distortion to some extent and thereby affecting its application performance.Therefore,La_1-xSr_xMnO₃?x=0.1?thin films were deposited on different orientation and lattice-mismatched substrates by pulsed laser deposition in this paper.The effect of deposition condition and the substrate-induced lattice mismatch on the structure,epitaxial relationship,electrical properties and conductive mechanism were analyzed.Firstly,La_0.9Sr_0.1MnO₃ thin films were deposited on single crystal MgO substrate by pulsed laser deposition in this paper.The influence of deposition parameters?laser energy density,deposition temperature,oxygen partial pressure?and annealing conditions?annealing temperature,annealing time?on the growth of La_0.9Sr_0.1MnO₃were systematically studied.In order to obtain high quality La_0.9Sr_0.1MnO₃ thin films,the films should be annealed at high temperature.With the increase of annealing temperature and annealing time,the crystallinity of the thin films was increased.Thus the appropriate annealing parameters were found to be 1273 K and 1 h.In addition,with the increase of laser energy density and oxygen partial pressure,the crystallinity of the films increased at first and then decreased.Furthermore,the higher deposition temperature contributed to the growth of the films.The single phase,smooth surface,compact structure and good crystallinity La_0.9Sr_0.1MnO₃ thin films were obtained under appropriate deposition conditions?laser energy density 1 J/cm²,deposition temperature 923 K,oxygen partial pressure 15 Pa?.Secondly,La_0.9Sr_0.1MnO₃ epitaxial thin films with?100?,?110?,?111?crystalline orientation and different degrees of lattice distortion were prepared on different orientation of MgO?100?,?110?,?111?substrates and different lattice-mismatched MgO?100?and SrTiO₃?100?,LaAlO₃?100?substrates under the appropriate deposition and annealing conditions.The X-ray diffraction and pole figure results showed that the films had high preferred orientation characteristics,and had an epitaxial relationship with the substrates.La_0.9Sr_0.1MnO₃ thin films grown on SrTiO₃ and LaAlO₃ substrates showed better crystalline,due to the smaller lattice mismatch between the films and the substrates.And then,the resistivity of La_0.9Sr_0.1MnO₃ thin films on MgO?100?,SrTiO₃?100?,and LaAlO₃?100?substrates was tested at the temperature ranging from 100 K to 400K by PPMS.With the increase of temperature,the resistivity of all the films were exponentially decreasing,showing the characteristics of semiconductor.Compared with the MgO substrate,La_0.9Sr_0.1MnO₃ thin films grown on SrTiO₃ and LaAlO₃substrates showed lower resistivity,because of the smaller lattice mismatch which caused lower lattice distortion.Finally,the relationship between resistivity and temperature was discussed using different conductivity model?Thermally Activated conduction,Variable-range Hopping,Adiabatic Small Polaron Hopping and Non-adiabatic Small Polaron Hopping?.The results showed that the variation of resistivity obeyed the Adiabatic Small Polaron Hopping conduction model.With the decrease of the lattice mismatch,the conductivity activation energy decreased.