Theoretical Study Of Electronic Transport And Photocurrent In Ni/Bp/NiMTJs

Electronic materials and devices are the foundation of modern information technology. With the development of spintronics and the rising demand for new devices, integrated circuit development shows two significant trends: on the one hand, integrated circuits are getting smaller,following a decade forward with nanoscale(<100 nm), this year has reached the technical level of 10 nanometers; on the other hand, some new materials such as grapheme and carbon nanotubes can be used in integrated circuits, which has been showing potential applications in the field of nano-devices. Studying of Low-dimensional nature of these materials is essential on the development of nanoelectronics devices. The black phosphorus(BP) have been fabricated in 2014. Compared to graphene, BP has a direct band gap, and a higher mobility than the transitional metal dichalcogenides(TMDs), which has attracted extensive research work. In this thesis, we carry out first-principles studies on the spin-depended electron transport properties and photocurrent of the Ni/MBP/Ni junctions.In chapter 1, we introduce the recent progress on the study of the BP, and the problems worthy of further study. The second chapter describes the theoretical method used in this work, that is, the state-of-the-art first principles quantization transport approach where density functional theory(DFT) is combined with the Keldysh nonequilibrium Green’s function(NEGF).In chapter 3, we investigate the non-equilibrium spin-polarized electronic transport in the two magnetic tunneling junctions(MTJs) of the Ni(111)/MBP/Ni(111) and Ni(100)/MBP/Ni(100). We find that(1) the Ni(100)/MBP/Ni(100) MTJ has the desired property where the spin injection and magnetoresistance ratio are not only large, namely TMR~40% and SIE~60%(PC), but also maintains at these values for a broad voltage range(0- 70 m V).(2) Ni(100)/MBP/Ni(100) configuration has the more superior spin-polarized quantum transport property than Ni(111)/MBP/Ni(111), which suggested that interface has significant impact on the TMR and SIE.In chapter 4, we investigate the equilibrium spin-polarized electronic transport properties of the Ni(100)/MBP/Ni(100) MTJ under mechanical strain and bending. For the uniaxial tension varying from 0 to 15%, the TMR ratio is enhanced with a maximum of 107% at the 10%y?(28) while the SIE for the PC increases monotonously from 8% up to 43% with the increased strain. Under the out-of-plane bending, the TMR overall increases from 7% to 50% with the bending ratio of 0-3.9%, and meanwhile the SIE of the PC is largely improved to around 70%.In chapter 5, we investigate the non-equilibrium spin-polarized electronic transport of the Ni(111)/MBP/Ni(111) MTJ under the illumination of the linearly and circularly polarized lights. We find that in 0.03 ~ 0.1V voltage range, TMR reaches a higher value around 30~50% at the polarization angle of about 30° and 150°. At the polarization angle between 45° and 135°, the SIE keeps a higher value than 60%. For the APC, with a maximum of 99% at the 0.08 V voltage. For the PC, the SIE has a higher value at about 30° and 150°. For the APC, there is a pure spin current about 0.33 at θ = 90°,with zero voltage.In chapter 6 gives a short summary of this thesis,and gives a prospective view of the study on the BP.