Preparation And Properties Of Eu-doped In₂O₃ Thin Films By Sol-gel Method

Indium oxide（In₂O₃）is an n-type transparent conductive oxide with a wide forbidden band,which is often used in flat panel displays,transparent electrodes,solar cells and other optoelectronic devices because of its excellent electrical conductivity and light transmission.The sol-gel method has become a film preparation method with obvious advantages due to its simple operation,low cost,low deposition temperature and large-area preparation.As many process parameters in the film preparation process affect the quality and properties of the film,the doping of rare earth elements can have an impact on the film’s physical properties.In this paper,unintentionally doped,Europium（Eu）-doped In₂O₃ films were prepared on quartz glass and sodalime glass substrates based on the sol-gel method.The effects of precursor liquid In3+concentration,spin-coating speed,annealing temperature,annealing time and different ratios of Eu doping on the properties of In₂O₃ films were analyzed by various test studies.The main conclusions are as follows:1.As the concentration of the precursor fluid increases,the crystallinity of the In₂O₃ film increases,forming a cubic crystal structure with a selective orientation along the（222）crystal plane,increasing grain size,decreasing lattice strain and dislocation density,increasing roughness and film thickness,and decreasing optical transmittance and optical band gap.When the precursor concentration is 0.7M,the grain size is about 11.14nm,the film thickness is about 109nm,the optical transmittance can reach 84%and the optical band gap is 3.77eV.2.As the spin coating speed increases,the diffraction peak intensity of the In₂O₃ films gradually decreases,the grain size decreases,the lattice strain increases,the film thickness decreases,the optical transmittance and the optical band gap both increase and the surface becomes flatter and denser.3.Both the increase in annealing temperature and the increase in annealing time result in stronger crystallinity,increased grain size,increased optical transmittance and increased surface porosity of the In₂O₃ films.4.The In₂O₃ thin films with an Eu doping ratio increased from 1%to 11%were prepared and analyzed.The results show that the doping of Eu does not change the cubic crystal structure of the In₂O₃ films along the（222）crystallographic plane,but with the increase in the proportion of Eu doping,the half-height width decreases,the crystallinity decreases,the lattice constant and grain size increase,the lattice strain decreases and the film surface becomes more uniform,smooth and dense.When the Eu doping ratio is 7%,the lattice constant is 10.141 and the grain size is about 11.63nm.The presence of the Eu-O bond indicates the successful doping of trivalent Eu.The optical transmittance and optical band gap increase with the increase of the doping ratio.The optical transmittance increases from 83%to 91%,and the optical band gap increases from 3.74eV to 3.79eV.All samples have a blue-green luminescence band at about 400nm,and the intensity is the highest when the Eu doping ratio is 3%.It shows that the selection of process parameters and Eu doping have important research significance for improving the physical properties of In₂O₃ films.