Study Of The Band Structure Of Zno At Different Acancy Defects Based On The First Principles

With the leap forward in artificial intelligence and the advent of 5G,the Internet market is demanding more and more performance from storage devices.Resistive random access memory(RRAM)is an important direction in memory development,offering huge advantages in terms of power consumption,performance,density and integration into production.The resistive phenomenon in RRAM devices is mainly controlled by the formation and breakage of conductive filaments,which are formed by the decomposition of the material itself,by metal ions formed by diffusion of the electrode material or by oxygen vacancy defects.Among these,zinc oxide is touted as the most promising material for varistor memory.In this paper,the first-principles calculation method of density functional theory(DFT)is adopted.The band structure of ZnO resistive random access memory with different coordination number and different concentrations is investigated by constructing two defective states of O vacancies as well as Zn vacancies.Firstly,ZnO cells were modelled for O vacancy and Zn vacancy defects in four,three and two coordination sites and vacancy concentrations of 12.5%,5.56%and 4.17%respectively.Secondly,the effects of O vacancy and Zn vacancy defects under different coordination on the energy band structure,density of states(DOS),geometry optimization process and energy change of ZnO were analysed.The DOS valence band peaks for different coordination vacancy defects are shifted towards the Fermi energy level.Among them,the three-coordination Zn vacancy defects are more likely to generate holes in the ZnO system than the O vacancy defects,and the ZnO cell DOS peak increases the most with the three-coordination Zn vacancy defects,and the electron localisation increases.Thus,the effect of vacancy defects on the energy state structure of ZnO at different concentrations was investigated on the basis of three-coordination vacancy defects.Then,the effects of the O vacancy and Zn vacancy defects on the band structure,DOS,geometry optimization process and energy change of ZnO at different concentrations of the three coordination numbers were investigated.It is found that the peak values of the total density of states(TDOS)and the partial density of states(PDOS)of the ZnO system and Zn atoms decrease as the concentration of the Zn and O vacancy defects increases from 4.17%and 5.56%to 12.5%,with the 3d orbitals of Zn playing a major role.The peak density of states of the Zn atoms at a concentration of 5.56%of the triple coordination number vacancy defect was also analysed to obtain the lowest peak density of states.The peak of atomic PDOS does not vary linearly with increasing vacancy concentration.Studies have shown that vacancy defects under three coordination number have a significant effect on ZnO band gap.The vacancy defects are most easily formed when the vacancy concentration is 5.56%under triple coordination,and the increase in the number of ions is favourable to the formation of conductive filaments connecting the upper and lower electrodes,enabling the switching between high and low resistance,thus improving the performance of ZnO resistive random access memory.The results of this thesis provide some theoretical guidance for the performance enhancement of ZnO resistive random access memory.