A Study On Preparation, Structure And Physical Property Of ZnO:Mn DMS And P-type ZnO:N Films

Zinc oxide (ZnO) is a new kind of Ⅱ-Ⅵ semiconductor materials with advantage of wide band gap, high exciton binding energy and strong emission of near ultraviolet area, thus it is widely applied for semiconductor devices. Doping technique is used to adjust the physical properties of ZnO for its practical application. In this thesis, diluted magnetic semiconductors doped with transition metal elements Mn and P-type ZnO doped with N are prepared.Diluted magnetic semiconductors, which can manipulate the charge and spin of electrons simultaneously, leading to a wide application in the field of spintronics device, attract more and more research interest in recent years. In these studies, the Mn-doped ZnO diluted magnetic semiconductor is highlighted for its great capability of being injected with a large number of spin carriers. So far, although researches on Mn doped ZnO at room temperature ferromagnetism are greatly reported, it remains a controversy whether the observed ferromagnetism is from Mn substitutional effect or segregations of Mn in ZnO material. The problem mentioned above is mainly due to the limitation of conventional analysis methods, such as ordinary XRD, with which it is difficult to probe the detailed structure of the magnetic Mn ions with relative low concentration in ZnO diluted magnetic semiconductors. In this work, a group of interesting results are obtained with the high sensitivity detective methods of synchrotron radiation X-ray diffraction (SR-XRD) and X-ray absorption fine structure spectrum (XAFS) technology, combing with the proton induced X-ray emission (PIXE) and superconductivity quantum interference device (SQUID) methods:1. A series of Mn doped ZnO film samples are prepared on sapphire substrate under different growth conditions by radio frequency magnetron sputtering method and SQUID tests show all samples have room temperature ferromagnetism.2. PIXE and SR-XRD results show that only Mn, without any magnetic impurities (e.g. Fe, Co, Ni) and no Mn clusters and secondary phases (e.g. MnO, MnO2, Mn2O3, and Mn3O4) exist. All the ZnO:Mn thin films are of wurtzite ZnO structure.3. EXAFS results indicate that Mn atoms are incorporated into ZnO crystal lattice through the substitution of Zn sites. According to the microstructure analysis, the ferromagnetism should derive from the substitutional effect of Mn atoms.Although ZnO devices (like the PN junction made of the same material) are strongly dependent on the preparation of high quality p-type ZnO, it is extremely difficult to proceed the p-type doping of ZnO due to the self-compensation effect caused by intrinsic defects. Theoretical calculations show that N is an excellent acceptor element in ZnO and can achieve the p-type doping of ZnO. However, the solubility of N in ZnO is so low that it is difficult to carry out p-type doping of N elements effectively with traditional methods. In this work, high concentration of N in ZnO p-type doping is obtained with thermal oxidation Zn3N2method and the corresponding results tested with methods of Rutherford backscattering (RBS), X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Hall are as follows:1. Zn3N2thin films are prepared by radio frequency (RF) reactive magnetron sputtering method, and then annealed in oxygen atmosphere at different temperatures. The structure transformation of the films under different thermal oxidation temperature is studied with RBS and XRD, showing that phase transition from Zn3N2to ZnO take place above300℃, and chemical reaction occurs at the interface between film and substrate on700℃.2. The variation of N content and valence state in the films under different thermal oxidation temperature were studied by XPS and corresponding results show that less N content are obtained at higher annealing temperature and N atoms are located in the substitutional position of the O atoms in the oxidated samples.3. The Hall tests show that the electrical conductivity alters from the n-type to p-type when the thermal oxidation temperature of400℃,500℃and600℃, indicating that the doping N in ZnO is an effective electron acceptor.