Theoretical Study On Doping Effect Of Ti Doped HfO₂ Based Memristor And Photocatalysis Characteristics Of C₂N/BlueP Heterojunction By First Principles Calculations

With the development of social intelligence,the requirement of information storage is higher and higher.Memristor（RRAM）is one of the best candidates for nonvolatile memory because of its advantages such as simple structure,low power consumption,high density,fast operation speed and strong compatibility with CMOS technology.HfO₂is a good resistive layer material.In order to further improve the resistance switching properties of HfO₂based RRAM,we calculated and studied the doping effect of HfO₂based RRAM and the effect of annealing treatment in different atmospheres through the first principles.The influence of doping and annealing treatment on the resistance switching properties is theoretically explained,which can guide the formulation of experimental scheme.In addition,the development of the contemporary society demands more and more energy.However,the mineral energy such as coal and oil on the earth become less,so it is urgent to seek new energy of clean and environmental protection.Since 1972,a large number of studies have shown that various semiconductor photocatalysts can use solar energy to decompose water to produce hydrogen.Solar energy is a clean and renewable energy,and hydrogen energy has many advantages,such as clean,efficient,safe,storable,transportable and so on.These advantages make photocatalytic water decomposition technology more and more studied by research workers.However,the photocatalytic efficiency of semiconductors is not high at present,so we study and explore the photocatalytic effect of new semiconductors by the first principle calculation method.Firstly,the Ti doping effect of HfO₂based RRAM is studied.The HfO₂supercell model with 96 atoms and the Ti doped HfO₂model with different concentrations are established by Materials Studio software.The formation energy of oxygen vacancy at various Ti doping concentrations is calculated.The results show that when Ti doping concentration is 3.13%,the formation energy of oxygen vacancy is the smallest,that is to say,more oxygen vacancies will be formed under the same operating conditions.Then the formation energy of oxygen vacancy at the optimum Ti doping concentration is calculated with the change of oxygen partial pressure and temperature.The results show that low oxygen partial pressure and high temperature are beneficial to the formation of oxygen vacancy.And the calculation of oxygen vacancy migration barrier energy shows that oxygen vacancy is easier to form near Ti doped atom.In theory,we simulated the annealing of nitrogen,oxygen and the prepared Ti-doped HfO₂model and calculating the migration barrier of oxygen vacancy,and found the theoretical results are consistent with the experimental results.Based on the density functional theory（DFT）method,the photocatalytic properties of C₂N/BlueP for water decomposition were studied in terms of electronic structure,band edge alignment,charge transfer,optical absorption and strain response.The results show that C₂N/BlueP heterostructure has appropriate direct band gap and inherent type-II band alignment,which is conducive to the spatial separation of photogenerated electron hole pairs.Compared with their monolayers,the optical absorption of hybrid heterostructures in the visible to UV region is enhanced.More importantly,the maximum value of valence band（VBM）is lower than the oxidation potential of water,while the minimum value of conduction band（CBM）is higher than the reduction potential of water,which indicates that the photocatalytic water separation potential of C₂N/BlueP hybrid structure is appropriate.In addition,by applying a stress perpendicular to the heterostructure（the interlayer compression is about 6%）,the band edge position and optical absorption can be improved,thus improving the photocatalytic water decomposition performance of C₂N/BlueP heterostructure.To sum up,this paper studies the challenges of science and technology and energy in modern society.The main purpose of this study is to improve the memory performance and find more efficient and feasible photocatalytic materials.The results show that the nitrogen annealed Ti-doped HfO₂based RRAM device has lower Forming voltage and SET/RESET voltage.The new heterojunction realizes the effective separation of electron hole pairs,and the optical absorption is improved compared with the single layer structure.At the same time,the effect of vertical stress on heterogeneous structure was studied,and it was found that the photocatalytic performance of heterogeneous structure was further improved when 6%pressure was applied,which provided a feasible photocatalytic material for the photocatalytic decomposition of aquatic hydrogen.