The Study Of Tuning Optoelectronic Properties In Correlated Oxide Thin Films

Oxide thin films have abundant crystal structures and physical properties,and have been widely used in optoelectronic devices,such as photodetection devices,transparent electrodes in photovoltaic cells and light-emitting diodes.The optoelectronic properties(band gap,dielectric constant,refractive index and absorption coefficient,etc.)of these oxide films are determined by the electronic structure near the Fermi level,which is also the basis for the design and application of optoelectronic devices.The electron correlation caused by electron-electron interaction in electron-correlated oxides cannot be simply replaced by the average potential field,resulting in its electronic structure cannot be understood by the energy band theory based on the single-electron approximation,which will directly affect its optoelectronic properties.It is also possible to break through the photoelectric performance bottleneck of conventional oxides(regardless of electronic correlation).Based on the above considerations,in this paper,we chose Y2(Ir1-xHfx)2O7(5d),SrMoO3(4d)and V2O3(3d)as the research objects,and carried out the control of their photoelectric properties.The pyrochlore structure A2B20 7 has rich physical properties under the action of electronic correlation and spinorbit coupling:Pr2Ir207 exhibits metallic behavior,Kondo effect and spontaneous Hall effect;Y2Ir2O7 exhibits insulator behavior(band gap is about 0.4 eV);the band gap of Y2Hf2O7 is 4.6 eV.The band gap of(Pr1-xYx)2(Ir1-xHfx)2O7 may be tuned to 0-4.6 eV,which will provide a material basis for the realization of broad-spectrum photodetectors.In the first part of this thesis,we mainly study the band gap tuning of the pyrochlore structure Y2(Ir1-xHfx)2O7.Many associated metals in electron correlated oxides have been reported as transparent conducting oxide(TCO)materials,where the electron correlation leads to an increase in the effective mass m*of the carriers to open the transparent window.The perovskite structure SrMoO3 has high electrical conductivity,and SrMoO3 thin films have been reported as n-type TCO materials,but the factors affecting the transparent conductivity are still unclear.The corundum structure V2O3 is a paramagnetic metal state at room temperature.Our research group has previously proposed that the V2O3 film can be used as a p-type TCO material,but how to further improve its transparent and conductive properties remains to be further studied.In the second and third parts of this thesis,we mainly conduct research on the regulation of the transparent conductivity of electron-related oxide SrMoO3(n-type)and V2O3(ptype)thin films.The main contents are as follows:Firstly,high-quality Y2(Ir1-xHfx)2O7(YHIO)thin films were prepared on YSZ(111)substrates by pulsed laser deposition.The structural characterization results of X-ray diffraction and transmission electron microscopy showed that the YHIO thin film was epitaxially grown on the YSZ(111)substrate.A wide range of tuning of the optical bandgap of 1.9-4.6 eV(x=0.5-1)of YHIO thin films is achieved by changing the Hf content.The theoretical calculation results show that the optical band gap gradually decreases with the increase of Ir content due to the stronger hybridization between the Ir 5d orbital and the O 2p orbital near the Fermi plane than the Hf 5d orbital and the O 2p orbital near the Fermi level.Secondly,high-quality SrMoO3 epitaxial films were prepared on LaAlO3(001)substrates by pulsed laser deposition.The electrical transport results show that the SrMoO3 film undergoes a metal-insulator transition as the thickness decreases,and the optical ellipsometry results show that the SrMoO3 film undergoes changes in the optical absorption in the visible region and the optical transmission window as the thickness decreases.The XPS results reveal that this originates from the change of the electronic structure near the Fermi surface.The oxygen content was changed by changing the oxygen partial pressure during the preparation of the SrMoO3 thin film.It was found that the optical transmittance did not change significantly with the oxygen content,but the resistivity showed a dependence on the film thickness with the oxygen content.As the thickness decreases,the oxygen content has an increasing influence on the resistivity.Finally,high-quality V2O3 epitaxial films were prepared on Al2O3(001)substrates by pulsed laser deposition.Lattice mismatch is used to introduce compressive stress in the film,and the electrical transport results show that the compressive stress suppresses the low-temperature antiferromagnetic insulating phase to exhibit metallic behavior in the entire temperature region,while increasing the electrical conductivity of the hightemperature paramagnetic metallic phase.The Hall effect results indicate that the increase in electrical conductivity originates from the increase in carrier concentration,and Raman spectroscopy further reveals that the underlying physical reason is the change in electronic structure,where compressive stress leads to an increase in the occupied state of the a1g orbital.The optical ellipsometry results show that the plasma energy of the V2O3 film under compressive stress is 1.6 eV(<1.75 eV),which ensures its optical transparency in the visible light region.Therefore,the compressive stress in the V2O3 film significantly enhances its transparent conductive properties.