The Preparation And Investigation Of Gan Based Diluted Magnetic Semiconductor Films

With the development of the semiconductor technology, the feature size of the transistorsshrinks from0.35μm to the most advanced22nm in the past ten years, which improved theintegration by thousands of times, while the insulating layer between the transistor devicesbecome thinner and thinner. With further development, when the thickness of the insulating layeris thin enough, there will be a quantum tunneling effect resulting in the failure of the insulationlayer, and thus cause the entire integrated circuit does not work. Moreover, the lithographyprocess is also a major bottleneck in the development of semiconductor technology. In short, thefeature size of the transistors can not shrink infinitely, and its development has been very limited.To further enhance the integration and performance of the chips must find another new way.The spintronics developed in recent years is expected to use both charge and spin ofelectrons in the dilute magnetic semiconductor (DMS) material, thus providing a broader spaceto improve the circuit performance and chip integration. The coupling between the intrinsicmagnetic moment of the magnetic ions and the electron spin leads to many novel physicalphenomena, such as magnetically induced insulator-metal transition, anomalous Hall Effect,bound magnetic polarons, giant Zeeman splitting, giant Faraday Effect and negativemagnetoresistance. These novel physical properties provide the conditions for the developmentof new technologies, which have broad application prospects in the fields of magnetic sensors,high-density non-volatile memory, optical isolator, semiconductor laser and spin quantumcomputers. Therefore, DMS materials have been concerned by scientists all over the world, andbecome a research hotspot. It is necessary to prepare new type diluted magnetic semiconductormaterials with room-temperature ferromagnetism for the development of practical spintronicdevices, which is also the focus of current research. In2000, the Science magazine reported thatthe Curie temperature of GaN-based diluted magnetic semiconductor materials may reach aboveroom temperature, since then a lot of the research teams extensively investigated the GaN-baseddiluted magnetic semiconductor materials. However, the experimental equipment, growingconditions, processing technology and doping element, etc. are all different, so the results are notuniform, even in the same kind of material. The origin of the ferromagnetism in DMS materialsis still controversial.In this dissertation, a lot of experiments have been carried out under a variety of experimental conditions, hoping to find the optimal conditions for preparing the ideal GaMnNDMS materials. AlGaN is one of the series of GaN-based materials, and GaN/AlGaNheterostructure based high-mobility transistors have many potential applications in the field ofthe ultra high frequency, high-temperature and high-power devices. We investigated theproperties of Tb doped GaN and AlGaN materials, and Sm, Cr co-doped AlGaN materials,expecting for a breakthrough in improving the Curie temperature. The main results are asfollows:1. The GaMnN films with the Curie temperature up to340K have been successfullyfabricated on the sapphire substrate by LMBE. The properties of the films strongly depend on thepressure of nitrogen gas. From our experimental results, the optimum nitrogen pressure forpreparing the GaMnN dilute magnetic semiconductor thin films is0.75Pa. The GaMnN thinfilms with desired magnetism can be obtained by adjusting the pressure of nitrogen gas.2. The as-grown GaMnN samples are amorphous. The post annealing process has a verystrong influence on the properties of the GaMnN thin films. The Mn2+and Mn3+ions coexist inour GaMnN samples, and their proportion varies with the annealing time, which has a veryimportant influence on the magnetic properties. Therefore, by controlling the annealing time, wecan obtain the GaMnN samples with good crystalline quality and specific magnetic properties.3. The lattice will be damaged partially during the ion implantation, resulting in thedegradation of the crystalline quality of the samples. The lattice damage may be partiallyrecovered by the post annealing process, but with a slight lattice expansion comparing with theas-grown sample. The GaN:Tb and AlGaN:Tb samples are all ferromagnetic at room temperature,which can be explained by the bound magnetic polaron (BMP) theory. We speculate that the Alatoms may strongly affect the total magnetic moment of the AlGaN:Tb samples, which requiresfurther research and feasibility studies.4. At room temperature, the Cr, Sm codoped AlGaN samples exhibit ferromagnetism andthe giant magnetic moment effect, which is more obvious in the sample annealed at900℃. TheGiant magnetic moments may be derived from two aspects: One is the coupling between the Cr3d and Sm4f electrons; another is the coupling between the Cr3+-BMP and Sm3+-BMP, whichdeserves further study.