The Growth And Properties Of Oxide Semiconductor And Magnetic Oxides By MOCVD

As a new field,spintronics has a wide application prospect.It increases the degree of freedom by controlling the electron spins without being limited by the size of the chip,which will replace the electronic charge as the carrier of information storage and transmission.Researches to achieve the emission of the spin polarized light emitting diodes(spin-LED)have attracted more attentions.Two kinds of main materials,i.e.,magnetic oxide and wide bandgap oxide semiconductor,which are the fundamental precondition to realize the oxide based spin-LED devices,are of more interests.This dissertation has investigated the wide bandgap epitaxial growth of oxide and metallic oxide systematically,focusing on two key techniques of ZnO thin films heteroepitaxy on highly mismatched sapphire substrates:the substrate pretreatment and buffer layer thickness optimization,and obtained the optimization technology of the ZnO thin film heteroepitaxy.Considering the technical difficulties in current ZnO p-type doping and the mature heteroepitaxy and p-type doping technology of GaN,the author has used the GaN material instead of ZnO as the substrate for the Fe304 film growth,and carried out the research of Fe3O4 MOCVD growth and the properties of the Fe3O4/GaN heterostructure.Research has revealed the influence of the thin film growth and annealing process on the structure and properties of the heterogeneous interface,and further developed a GaN based spin-LED prototype device with spin injection.Detailed results are listed below:1,Systematic studies of the sapphire substrate pretreatment,substrate pretreatment temperature,and high temperature annealing process on the ZnO buffer layer surface morphology and the crystalline quality have been carried out.We pointed out the mechanism of the sapphire substrate high-temperature "nitriding" on the improvement of the ZnO buffer layer morphology and crystalline quality and found the optimal point of the substrate pretreatment temperature.The necessity of high temperature annealing of ZnO buffer layer and physics mechanism on improving the ZnO buffer layer morphology and crystalline quality were pointed out.Through the above systematic research,we found the technical approaches to achieve high quality ZnO buffer layer,which laid a solid foundation for the optimization of the epilayer on the ZnO buffer layer.2,In-depth analysis of the dynamic mechanism of the ZnO epitaxial growth on largely mismatched substrates reveals the role of the buffer layer in the ZnO epitaxial growth.It has been pointed out that one buffer layer with an appropriate thickness can release a large amount of strain energy,provide a lattice-matched homogeneous substrate for the two-dimensional terraced growth,as well as confines the dislocation structure defects and ensures the epitaxial layer with low dislocation density and high crystalline quality.The study found that the smooth surface formed by the ZnO buffer layer with an appropriate thickness plays a key role on the surface morphology of the high temperature epitaxial layer.Flatness of the buffer layer and lateral growth of epitaxial layer will codetermine the crystalline quality of ZnO epitaxial layer.Through the systematic study,we obtained the optimal point of the buffer layer thickness.In addition,we found the film conductive behavior was mainly determined by the electrical properties of the buffer layer.The corresponding ZnO epitaxial layer would inherite the dislocation and defect density distribution of the buffer layer,which resulted in the consistent carrier concentration with the buffer layer thickness.3,High quality Fe304 film was successfully prepared on the GaN substrate by MOCVD method.Different oxygen sources were used to explore the suitable growth condition.Our study found that the annealing process will cause diffusion behavior of Ga at the Fe3O4/GaN heterostructure interface.The Ga diffusion formed a buffer layer between GaN and Fe3O4,and improved the quality of the film crystallinity however reduce the magnetization.We thought the annealing process was not conducive to the preparation of the Fe3O4 film.Further,the MOCVD-grown Fe3O4 film was carried out on the pretreated GaN substrate.By using thermal oxidation methods,the Ga2O3 barrier layer was formed at the Fe3O4/GaN interface,which provides a new idea for the spin electron injection.An obvious interdiffusion phenomenon was found at the Fe304/GaN interface.On this basis,combining with the ready-made technologies in fabricating the GaN-based inversed LED device structure,the spin-LED proto-type device was successfully achieved by the deposition Fe304 film on the GaN-LED.