Structure,Transport And Magnetic Properties Of Transition Metal Doped SiC/Cu Diluted Magnetic Semiconductor Ultrathin Multilayer Films

Since SiC is a new type of material that is easily doped into a wide bandgap semiconductor,its preparation process is also relatively mature.We chose SiC as the research object of this thesis.However,due to the insufficient performance of the non-magnetic material alone,we perform co-doping of magnetic and non-magnetic materials to improve the properties of the material.At the same time,the potential giant magnetoresistance of SiC semiconductors was studied.By magnetron sputtering,we prepared SiC/Cu multilayer films,which were alternately deposited by multilayer film method,which increased the contact area between SiC and Cu,and solved the problem of low saturation magnetization of Cu.It is roughly divided into two aspects of preparation research,one is to co-doped magnetic and non-magnetic materials into SiC,through the co-doping of Fe and Ni to improve the film properties,and the Fe,Ni co-doped SiC/Cu multilayer film samples.The transport,structure and magnetic properties were studied.Another study was conducted on the giant magnetoresistance of the annealed multilayer film.The effects of annealing on the structure,magnetoresistance and magnetic properties of the SiC/Cu multilayer film were analyzed.The periodic structure of Fe-co-doped SiC/Cu multilayers with different thickness of Cu layer was characterized by X-ray reflectance spectroscopy,and the single layer thickness and single periodic structure were at the level of?.X-ray photoelectron spectroscopy proves the existence of Cu-C and Fe-Si bonds,and the element of Cu exists in the form of elemental Cu and Cu~+.The fine structure of X-ray absorption and its fitting results showed that Fe atoms enter interstitial sites partly,while Cu atoms enter SiC in the form of substituted Si and Cu clusters.Transport measurements show of multilayers are above 10~222 orders of magnitude.and carrier concentration decreases with the increase of the thickness of the copper layer.Mott transition is the main transport mechanism of the samples.The calculation of the density of states shows that the ferromagnetism of the system originates from the p-d exchange of Fe3d,Cu 3d and C 2p,Si 2p.The magnetic measurements show that all the samples have room temperature ferromagnetism,and the maximum saturation magnetization reaches 8.2emu/cm~3,which decreases with the increase of the thickness of the copper layer.This is because the carrier concentration decreases with the increase of the thickness of the copper layer,and the p-d exchange effect of the system weakens,thus the saturation magnetization decreases.Samples annealed in vacuum at lower temperatures.After annealing below the first melting point temperature of nano-Cu,the SiC layer of the annealed sample appears tiny SiC crystallization,and the Cu atoms are partially coupled into the SiC layer and substituted for the Si site,which exists in the valence form of Cu~+.All multilayers have P-type semiconductor characteristics.Mott transition is the main transport mechanism of samples,and all of them have room temperature ferromagnetism.Hall measurements show that the carrier concentration Pc decreases with the increase of the thickness of the copper layer,and the saturation magnetization Ms increases with the increase of annealing temperature.The ferromagnetism of the system is still due to the carrier-regulated p-d exchange.The annealed samples show positive giant magnetoresistance effect.The magnitude of magnetoresistance is directly related to the thickness change of the single layer of the multilayers.The maximum magnetoresistance is 700%at 30K test temperature.