| The emerging scientific field of spintronics becomes a focus of attention recently, because the spin-based electronic devices have several novel advantages over the conventional charge-based devices regarding processing speed, much higher integration densities, and decreased power consumption. As one of the most potential candidates for these spin-based electronic devices, GaN-based diluted magnetic semiconductors (DMSs) have been attracting extensive interests. The origin of ferromagnetism of the GaN-based DMSs is still under controversy despite the successful fabrication of them. In this dissertation, the microstructures, optical, electrical and magnetic properties of GaN doped with the transition metal Cr grown by molecular beam epitaxy (MBE) are carefully investigated. The main contents and results are listed as follows:1. GaN and A1N epilayers doped with Cr are prepared on sapphire by a radio-frequency MBE. The parameters of growing such as the temperature of the substrates and the cells are optimized. It has been confirmed that Cr in GaN is predominantly trivalent when substituting for Ga (Al) and the Ga1-xCrxN and Al1-xCrxN epilayers have ferromagnetic orders at room temperature.2. Ga1-xCrxN thin films with and without Si doping have been prepared by MBE. The microstructural characteristics, optical, electrical and magnetic properties of the films have been studied. A small amount of Cr2+ states are appeared caused by the electron doping. The increase in Cure temperature, and the reduction in the saturation magnetization in Ga1-xCrxN:Si are observed and discussed.3. Magnetic and electronic properties of amorphous CrN thin films grown on MgO substrates by MBE have been investigated. The magnetic property of these films show a ferromagnetic behavior even at room temperature, and can be interpreted by the percolation theory of magnetic polaron. The results of electrical conductivity are explained by the variable-range-hoping theory of the Mott and Davis model.
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