First-Principles Study On Ferroelectric Properties Of Bismuth Titanate And The Electrical Properties Heterostructure Of HfO₂/Si

The composite structure of ferroelectric/semiconductor materials is one of the dielectric/semiconductor composite structures.Because of the composite structure,the energy band and the structure of the interface will be changed,thus new physical properties will appear.But the mutual diffusion of the atoms will cause the charge caputure which will influence the interface quality.In order to reduce the influence of this phenomenon on the device,we always add the insulation layer between ferroelectric film and semiconductor film,which is also known as the buffer layer,to form a ferroelectric film-buffer layer-semiconductor structure.Therefore,ferroelectric materials and buffer layers have become a hot research topic in today's academia.In this paper,through the combination of experimental and theoretical methods,we focus on the effect of annealing temperature on the quality of ferroelectric materials(Bi,Nd)4Ti3O12,and base on the density functional theory and use the first principle,studying the basic properties of the heterojunction of semiconductor Si and buffer layer Hf O 2.We prepare the(Bi,Nd)4Ti3O12 ferroelectric thin films,and focus on the influence of annealing temperature on the quality.Through the analysis of Bi4Ti3O12 ferroelectric material modeling,we discuss the band structure,density of states,the important parameters of difference charge density distribution.It is found that A-site ions play a significant role in the polarization process of the system,and if other ions are selected to replace A-site bismuth ions,the resulting bonding changes will induce the charge transfer between ions,and the polarization properties of the BIT system will change.We build the body structure and the surface structure of Hf O 2 and Si,which help us analysis the band structure,density of States,surface relaxation.The study shows that the surface structures of the two materials has bigger relaxation.But the surface of HfO2 has more complex structure,the atomic relaxation is larger than the surface of Si.It is found that O3 electron states and O4 electron states are mainly distributed in-18 eV to-15 eV,-5 eV to 0 eV and 2.5 eV to 7 eV,O atom of 2p electrons and Hf atom of 6s electron occurrence orbital hybridization,forming strong covalent bond.The HfO2 is mainly based on the O-2p orbit,and the O-2p orbital electrons.And the valence band are shifted to the high-energy region.The result of the electron-state migration to the high energy region makes the electrons of the HfO2 surface system easily excited and their stability weakened.The electronic properties of the HfO2-Si heterogeneous structure are discussed from the interface atom structure,and the interfac e distance is determined by total energy at different interface distances after full relaxation of the heterogeneous interface structure,it is found that when the interfacial distance of heterogeneous junction is d=1.55 ?,the heterogeneous junction structure is always the smallest,and the heterogeneous structure is the most stable.We analysis the heterogeneous structure from the energy band,the PDOS and the difference charge density.The bandwidth of the heterogeneous is 0.17 eV,we found that the Si-Si bond is the strongest,therefore its covalent effect is also the strongest,the O-Si bond is relatively small.Finally,the band deviation of the heterogeneous knot is 3.37 eV by calculation.