The Transport Properties And Optoelectronic Properties Of Graphene-Graphyne Heterojunctions

More and more carbon materials have attracted people's attention since the twentieth century,and the design and research of nano-devices based on carbon materials have gradually become a hot topic.Among them,graphene and graphyne are expected to be used in a variety of scientific fields owing to their unique physical and chemical properties.And they are considered to be promising carbonaceous materials in the future.In this paper,we designed several functional nanoribbon heterojunctions based on these two carbon materials,which provided new ideas and new ways for the study of low-dimensional carbon materials with important theoretical and practical value.In the first chapter of this paper,we introduced the concept of spintronics and the research progress of graphene,graphyne and their nanoribbons.At the same time we presented the research process and prospect of semiconductor heterojunction in detail,and clarified the research contents and meaning.In the second chapter,we demonstrated the density functional theory,the non-equilibrium Green function method and the ATK and Nanodcal softwares used in this paper.Using density functional theory and non-equilibrium Green's function method,we designed several zigzag graphene-graphyne nanoribbon heterojunctions devices and investigated their spin-dependent transport and optoelectronic properties in Chapter 3 and 4.The details are as follows:First,we discussed the spin-transport properties of these devices over a certain bias range.Our results show that the heterojunctions have outstanding giant magnetoresistance(GMR)effect.The GMR value is as high as 106 %.According to the symmetry and connection way,for the ferromagnetic states the heterojunctions may produce two spin currents and exhibit significant rectification behaviors.Second,we investigated the current generation of these devices under light irradiation.We found spin-polarized photocurrents can be generated by irradiating the devices with infrared,visible or ultraviolet light.More importantly,in these heterojunctions we found that the behavior of the spin-up(spin-down)photocurrent for the ferromagnetic state is similar to that of the spin-down(spin-up)photocurrent for the antiferromagnetic state.This novel effect provides an efficient way to control the spin transport in the systems.We also make it clear that for the current generated under the bias and light,the corresponding microscopic mechanisms are completely different.In the fifth chapter,we have a detailed summary of the full text.