First Principles Study On Two-dimensional Semiconductor And Ferroelectric Gate-controlled Field Effect Transistor

With the discovery of two-dimensional graphene,its unique electronic properties and broad application prospects have attracted the interest of researchers in its research and other two-dimensional materials,and the two-dimensional material family has also been growing.In this paper,according to the density functional theory,a new two-dimensional semiconductor material with high carrier mobility and light absorption is predicted,and a ferroelectric gate-controlled field effect transistor with high switching ratio is proposed by first-principles theory.This paper is divided into three parts.The first part is the first chapter,which briefly introduces the development,properties,preparation and application of two-dimensional semiconductor materials and ferroelectric materials.The second part is the second chapter,which introduces the theory of quantum mechanics,density Functional theory,exchange of associated functionals and software packages used;the third part,including Chapters 3 and 4,is the main theoretical calculation of this paper.The third chapter is the theoretical study of two-dimensional SnP₃.Although bulk SnP₃has been fabricated by experiments in the 1970's,its electronic and optical properties within several layers have not been reported.Here,based on first-principles calculations,we have predicted two-dimensional SnP₃ layers as new semiconducting materials that possess indirect band gaps of 0.71 eV?monolayer?and 1.03 eV?bilayer?,which are different with the metallic character of bulk structure.Remarkably,2D SnP₃ possesses high hole mobility of 9.171×10⁴cm²V^-1s^-11 and high light absorption(¹0⁶ cm^-1)in the whole visible spectrum,which predict2D SnP₃ layers as prospective candidates for nanoelectronics and photovoltaics.Interestingly,we found that 2D SnP₃ bilayer shows similar electronic and optical characters with silicon.Considering the great success of silicon-based microelectrics and photovoltaics,our results may benefit the related researches at nano scale.In the fourth chapter,a new two-dimensional van der Waals heterostructure ferroelectric gate-controlled field effect transistor?VDWh-FET?is studied.Traditional bulk ferroelectrics have been used to build field-effect transistors?FET?devices,and the barrier height of intercalated tunneling materials is modulated through the reverse of ferroelectric polarization.Although many schemes have been proposed to improve the performance of these FET devices,their On/Off ratio is still not satisfied since modulation of the barrier height is limited.Here,we proposed a high on/off ratio FET based on van der Waals heterostructures with layered ferroelectrics as gate substrates.Using typical bilayer materials?graphene?as tunneling layers,we found that reversing the polarization of top ferroelectrics can lead to the open and close of tunneling barrier through insulator-metal transition of intercalated bilayer,which is totally different with traditional FET devices.Since the insulator-metal transition is accompanied the tremendous changes of the electric conductivity,a high On/Off ratio is naturally qualified for real applications in devices.Furthermore,our first-principles calculations and tight-binding model analysis demonstrated that such phenomena are independent with the stacking order of ferroelectric gates.Thus,the explored results provide a bright prospect of 2D FET in future electric devices with thickness down to nanoscale.