Study On Optical Properties And Ferroelectric Propertiesof H-LuFeO₃

The polarization of ferroelectric materials can be act as build-in electric field to separate the photon-generated carrier,so that they can realize open-circuit voltage above optical band gap.This special photovoltaic effect provides a feasible way to break through the theoretical conversion efficiency of traditional photovoltaic cells,and shows a wide application potential in the field of new energy.However,most of traditional ferroelectric material's band gap are about 3 eV,which can only absorb a little part of solar energy,limiting the development of ferroelectric photovoltaic materials.For ferroelectric materials,the more narrow band gap thay have,the more solar energy they can absorb.Therefore,researchers have focused on the narrow band gap multiferroic materials,such as h-LuFeO₃.However,the low polarization intensity and optical absorption coefficient of h-LuFeO₃ hinder itself application in photovoltaic field.How to reduce the band gap of h-LuFeO₃,improve its optical absorption properties and ferroelectricity are the series of key issues of h-LuFeO₃ in ferroelectric photovoltaic field.In this paper,the band gap and light absorption properties of h-LuFeO₃ are studied by epitaxial strain control,and the ferroelectric properties of h-LuFeO₃ are improved by using buffer layers.The effects of S doping and In doping on the band gap,optical absorption coefficient and polarization properties of h-LuFeO₃were studied by first principles.The detail contents of this paper are shown as follows:?1?The effects of epitaxial strain on the light absorption and ferroelectric properties of h-LuFeO₃ were studied.The films of h-LuFeO₃ were grown on substrates with different lattice mismatches to provide different extent of epitaxial strain for h-LuFeO₃ films.The results show that compared with h-luFeO₃/Al₂O₃ thin film samples,the in-plane compression strain of h-LuFeO₃/Al₂O₃ thin film samples increases,and the c-axis of thin film increases.The band gap decreased from 2.04 eV to 1.96 eV,and the light absorption coefficient increased accordingly.There are many defects and poor ferroelectric properties of h-LuFeO₃ films grown at low temperature.The ferroelectric properties of the samples can be improved by decreasing the lattice mismatch between the film and the substrate and adjusting the epitaxial strain.?2?Using the first principle,the electronic structure and optical properties of the intrinsic h-LuFeO₃ are studied,and the reasons for the improvement of the optical absorption properties of h-LuFeO₃ are explained.The results show that Fe-O orbital hybridization at both ends of h-LuFeO₃ band gap is strong,and the calculation of optical properties shows that increasing Fe-O orbital hybridization along c-axis of h-LuFeO₃can enhance its light absorption properties.?3?In order to further study the methods to improve the ferroelectric polarization and light absorption properties of h-LuFeO₃,the improvement effect of In doping and S doping on h-LuFeO₃ band gap,light absorption coefficient and polarization intensity was studied by using the first principle.The results show that the substitution of In atom for Lu atom makes the h-LuFeO₃ crystal cell stretch along the c-axis,and the lattice constant c/a ratio increases.Enhanced h-LuFeO₃ Fe-O orbital hybridization along the c-axis,and thus improved polarization and light absorption performance.S doping improves the optical absorption performance of h-LuFeO₃,and the calculation results of optical properties and polarization are found through combined analysis.The ferroelectric polarization of h-LuFeO₃ is related to the change of light absorption coefficient.