Study On Transport Properties In Spin Valve Device Based On The Two-dimensional Black Phosphorus

Recently,two-dimensional(2D)van der Waals crystal materials,such as graphene,transition metal dichalcogenides(TMDs),have attracted wide attention due to their excellent physical,chemical and mechanical properties.Black phosphorus(BP),a newly identified 2D nanomaterial,has been demonstrated to be an appealing candidate material for nano-electornics and opto-electronics owing to its exotic physical properties such as thickness-dependent tunable band gap and high carrier mobility.In addition,it is predicted that BP has a long spin diffusion length,which makes it suitable for developing spintronic devices.To our best knowledge,there is no report on spin transport in BP nanodevice.In this dissertation,the fabrication and transport properties of BP and spin valve device based BP have been studied via mechanically exfoliating BP crystal and micro/nano fabrication process.Firstly,the field-effect transistors(FETs)based on pure BP and Te-doped BP were respectively fabricated.The transport properties have been measured and BP FETs exhibit ptype conductive behavior,large ON/OFF ratio and high carrier mobility.Meanwhile,it is found that Te-doping can improve ambient stability of BP FET devices.This has laid a good foundation for subsequent spin valve research.Secondly,spin-valve devices based on BP have been fabricated,in which a few-layer BP is sandwiched by two Permalloy electrodes and the BP layer serves as nonmagnetic spacer layer.The transport properties of BP spin valve devices have been characterized by physical properties measurements system(PPMS).The devices show spin-valve effect from room temperature to low temperature with a MR of 0.57% at 4 K.The temperature dependence of the device resistance reveals that the BP layer works as a metallic layer between two ferromagnetic electrodes.The results provide a possible approach to use the emerging BP nanomaterials for future spintronics applications such as magnetic memory and logic devices.Thirdly,the lateral spin-valve devices have been fabricated and their properties were measured by PPMS.A magnetoresistance effect of 0.27% at 10 K was achieved while no obvious magnetoresistance behavior occurs at room temperature,which may be ascribed to the poor interface between ferromagnetic electrodes and BP nanomaterials.