Physical And Electrical Properties Of Hexagonal Boron Nitride

Since the discovery of graphene in 2004,graphene and many other two-dimensional(2D)materials have aroused much attention of scientific research due to their unique properties,more and more studies reported application of 2D materials in electronic devices could improve the properties of electronic devices.Moreover,Hexagonal Boron Nitride(h-BN),as a novel 2D layered insulating material,has a wide band gap of～5.9 eV,a dielectric constant of～3,and exhibits higher reliability than transitional metal oxides(TMO)when exposed to an electrical field.Besides,h-BN has a very high mechanical strength and excellent chemical stability,which makes it promising to be one of the best dielectric materials in electronic devices.Although now h-BN has been used to improve the properties of electronic devices in field effect transistors and memristors,it is still not enough,we should further study the properties of h-BN in depth.Since band structure of semiconductors and insulators plays an important role in photochemistry and microelectronics,in the first part of this thesis,we measured optical band gap,the energy difference between the valence band and Fermi level and work function of the h-BN stack using Ultraviolet-visible spectroscopy(UV-vis)and Ultraviolet Photoelectron Spectrometer(UPS).We also studied the position of the valence band and conduction band with respect to vacuum level,providing more applications of h-BN in microelectronics and photochemistry.Besides,in the second part of this thesis,we fabricated h-BN based electronic devices by photolithography and electron beam evaporator and we studied electrical properties of h-BN based electronic devices at different temperatures.Through experimental data and simulation analysis,we demonstrated that h-BN based electronic devices shows clear temperature dependence of current,that is to say,the current level at the same bias increases with the temperature increasing,and it is mainly dominated by the temperature dependence of band gap of h-BN stack and band gap temperature coefficient we calculated is-6 meV/K,making it possible for h-BN based electronic devices to be applied in temperature sensors.On the other hand,as the rapid development of information technology,people have more and more requirements on information storage devices.Nowadays,memories have not met people’s requirements on high density,high speed and low power consumption.Therefore,it is necessary to develop high-performance memories to solve this urgent problem.To overcome current problems of non-volatile memories,resistive switching memristor has gained much attention due to its unique properties,the outstanding advantage of resistive switching memristor is promising to be high-density memory.Many studies have shown that resistive switching memristors using 2D materials as switching media exhibit excellent device properties.In the third part of this thesis,we fabricated resistive switching memristors with the cross-point structure using h-BN as switching media,which have small device size.h-BN based resistive switching device shows very nice resistive switching property and it shows smaller cycle to cycle variability at the same device.Furthermore,we found that almost all the devices show nice resistive switching property on our sample and they show the smaller device to device variability.Besides,we also use Ag as the top electrode and get very stable threshold resistive switching behavior,making it possible to be used as a selector,which could solve the problem of leakage current existed in 3D stacking crossbar memory cells.