Iron-doped zinc oxide films and nanostructures for spintronics

Diluted magnetic semiconductors (DMS) have been attracting considerable research efforts, as they will play important roles in the next generation of spintronics devices. One of the major technical challenges for spintronics is to increase the Curie temperature to room temperature for practical device applications. Among the available semiconductors, ZnO and GaN are the most promising materials as it is predicted to have carrier mediated ferromagnetic ordering up to room temperature. ZnO is the superior candidate in terms of high solubility of transition metal (TM) ions and low growth temperature.;This dissertation addresses growth and characterizations of Fe ions doped ZnO films and nanostructures for spintronics. The Fe ions are introduced into ZnO by ex-situ doping through ion implantation, as well as by in-situ doping during metalorganic chemical vapor deposition (MOCVD). The material properties, including structural, morphological, chemical, optical and magnetic properties are characterized. The results show that ion implantation can introduce Fe and Mn ions into ZnO without substantially degrading ZnO quality. Ferromagnetism up to room temperature is observed. The in-situ Fe doping during MOCVD has advantages over the ex-situ doping including uniform dopant distribution and better crystallinity. High quality ferromagnetic Fe-doped ZnO films and nanostructures are achieved using MOCVD for the first time. Comprehensive characterizations and analysis are conducted for both ion implanted and MOCVD grown Fe doped ZnO films and nanostructures. Additional doping in Fe-doped ZnO films and nanostructures with compensating dopant Li using diffusion and n-type dopant Ga are demonstrated using MOCVD for the first time. Li doping greatly enhances the ferromagnetism, while Ga doping completely quenches the ferromagnetism. The Fe-doped ZnO/ZnO heterojunction based magneto-resistive device is demonstrated for the first time. The device shows positive MR at low applied field and negative MR at high applied field.