The Design Of P-N Junction Based On Graphene Nanoribbon

The development process of electronics is a process of continuously pursuing electronic devices with small size,good performance and low cost.With the continuous development of the electronics industry,the size of electronic devices is gradually approaching the size limit of traditional semiconductor devices.In order to the continuous development of electronic industry,researchers are turning their attention to micro-nanoelectronic devices.The developments of two-dimensional materials in recent years has made people see their great potential in device design.Because of the excellent performance of graphene,it has attracted the attention of a large number of scholars and has been extensively studied in device design.The P-N junction plays an important role in logic circuits,and people have been paying close attention to the design and research of P-N junctions.Designing devices based on two dimensional materials can take advantage of superior performance of two dimensional materials.Graphene has high mobility and good thermal conductivity characteristics and is suitable for fabricating low-power,high-performance devices,but two-dimensional graphene is a zero-gap material that cannot be directly used for device fabrication.In this paper,the charge transport and spin transport properties of boron-doped and nitrogen-doped graphene nanoribbons P-N junctions are studied by the density functional theory based on non-equilibrium Green's function method.The main contents and conclusions are as follows:1.The boron and nitrogen atoms are used to replace the carbon atoms in the left and right electrode edges of the graphene nanoribbons.Four kinds of P-N junctions are constructed considering the position of the dopant atoms and whether the dopant atoms are hydrogenated.The intermediate connection part adopts the form of V notch.For the P-N junction with boron and nitrogen atom hydrogenation,the I-V curve not only exhibits significant rectification characteristics,but also exhibits negative differential conductance characteristics.By the analysis of molecule junctions projected selfconsistent Hamiltonian(MPSH),the electrode band and transmission spectrum shows that after doping hydrogenation,the energy bands of the left and right electrodes form a large energy gap near the Fermi level.Therefore,as the bias voltage changes,the energy bands do not overlap in the bias window,and since the non-overlapping under the positive and negative biases does not occur together,these led to the emergence of high rectification ratio rectification.Before the energy bands of the left and right electrodes are not completely separated in the bias window,as the bias window increases,the transmission peak in the bias window increases,and the transmission peak in the bias window decreases as the energy band gradually separates.In addition,the intensity is also gradually weakened,so that the current gradually decreases as the bias voltage increases,and a negative differential conductance phenomenon occurs.2.The spin density analysis shows that the doped graphene nanoribbons have ferromagnetism,and the spin transport properties can be studied.From the zero-bias transmission spectrum,it can be seen that the spin-up and spin-down transmission peaks undergo significant spin separation,exhibiting spin polarization and spin rectification in the I-V curve.By the analysis of MPSH,the electrode band and transmission spectrum shows that bands of the graphene nanoribbon electrode doped with boron and nitrogen atoms occur spin degenerate.The transmission spectrum at low bias produces a distinct spin transmission peak separation,and the boron atoms at the edges form a spin-up electron localized state,causing the spin-up energy bands that overlap each other in the bias window not contribute to electron transmission.So the energy gap of the spin-up energy band of the boron-doped electrode becomes larger near the Fermi level,which is much larger than the spin-down energy band gap,which leads to the occurrence of spin polarization and spin rectification.The thesis is divided into five chapters.The first chapter introduces the development status of low dimensional transport systems and the research status of P-N junctions based on graphene.These are the study background of this thesis.The second chapter is the theoretical method,which mainly introduces the density functional theory and the method of non-equilibrium Green's function;The third chapter mainly discusses and analyzes the phenomenon of giant rectification and negative differential conductance induced by boron and nitrogen atoms doping in zigzag graphene nanoribbon devices;The fourth chapter mainly discusses the doping of boron and nitrogen atoms can induce the perfect spin polarization and spin rectification in the zigzag graphene nanoribbon device and analyze the nature of perfect spin polarization and spin rectification with high rectification ratio;The fifth chapter summarizes the previous work and puts forward the prospect.