The Study On Preparation And Ferromagnetic Properties Of Transition Metal Doped ZnO Thin Films

Diluted magnetic semiconductors (DMS) combine the electron transport properties of semiconductors and the memory characters of magnetic materials. This is crucial for the new generation of spintronic devices. Due to the incorporation of transition metal ions, DMS exhibit some novel properties as compared to conventional semiconductors. As a result, investigations on DMS are quite significant from both viewpoints of fundamental research and device applications. The research on diluted magnetic semiconductors is one of the frontiers of modern physics. As one of the most promising DMS candidates, ZnO has been receiving great attention recently. Room temperature ferromagnetism for most 3d transition metal doped ZnO has been reported. Among them,V, Co, Ni, and Mn doped ZnO are the most widely studied. Although remarkable advances have been achieved, there still exist some obstacles in this area. Here we report our efforts on this topic.1. ZnO:TM(Co, Fe, Ni, Mn,V) thin films are dopisited by magnetron reactive sputtering. The XRD results show that all the films are mainly along c-axis orientation. XPS spectropy demonstrates all the transition metal exists in oxide phase and no transition metal cluster are detected in our films. For transiton metal(Co, Ni, Mn) doped ZnO thin films, the transimittance of them decrease with increasing the doping content. The reason of the observed phenemenon is the distortion of the films structure. The optical transmittace of the ZnO:V and ZnO:Fe thin films firstly decrease and then increase with increasing the doping contents. This is due to the changes of the films' structure. The V and Fe doping concentration is lower, the films are mainly along c-axis orientation. When the doping concentration increases further, the films change from polycrystalline to the amorphous. This can lead to the decreasing of the dispersion, which can increase the transmittace of the films.2. ZnO:TM thin films we prepared show no room temperature ferromagnetism except ZnO:Mn and ZnO:V thin films. The origin of the ferromagnetism may be the bound magnetropolaron.3. The influence of the sputtering parameter (total pressure, oxengy partial pressure and substrate temperature) on the ZnO:V thin films'structure, surface morphology and optical properties are studied.4. ZnO:V films are fabricated by reactive magnetron sputtering on glass substrates. ZnO:V thin films are annealed in air and in vacuum with different temperature. The thin films annealed blow 500℃have wurtzite structures. The ferromagnetism of the films annealed in vaccum is enhenced but the ferromagnetism of the films annealed in air were decreased. This demonstrate that the ferromagnetism origin from BMP deduced by the O vacancy and the V doping.5. ZnO:V thin films are also deposited on silicon wafer. All the films are c-axis oriented. Although the films quality is better than that of the films deposited on glass substrate, the ferromagnetism of the films on silicon is weaker than that of the films on glass. It reflects that the ferromagnetism of the ZnO:V comes from BMP deduced by the the defects and the V doping in the films.6. We have investigate the electronic structure of ZnO:Mn by adopting the ab-initio study of plane wave ultra-soft pseudo-potential technique based on the density function theory(DFT). The structure, band structure, density of state are studied.The calculated results are revealed that Mn-doping changed the band gap of the films, which increase with the increasing of the Mn content. The difference of density of state of the spin up and spin down makes ferromagnetism of the ZnO:Mn.