Study on Polycrystalline Nitride Semiconductors and Applications to Electric Field Emission Electron Sources and Visible Wavelength Region Fluorescence Substances

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From the polycrystalline GaN grown on Mo metal substrate, low threshold field of 6.4 V/μm was obtained for the electric field electron emission. To effectively reduce the field emission tunnel barrier height, thin AlN layer was formed on GaN surface and the reduction of threshold field was realized : the reduction of electron affinity was 0.8 eV.To control the grain structure and to improve the emission characteristics, GaN was grown on Si substrate with a thin SiO_2 layer. GaN nanorods were self-formed and the greatly improved field electron emission was obtained with a threshold field of as low as 1.25 V/μm : The emission current density was as large as 2.5 mA/cm^2 at 2.5 V/μm. Together with the strong adhesion characteristics to substrate, the GaN nanorods are promising to the application to the field emission electron devices.Strong sharp photoluminescence emission was obtained from the rare-earth-doped GaN,GaEuN,GaGdN and GaDyN, in the visible wavelength region. It was shown that these light emissions are due to the atomic level transitions at the rare-earth atoms because of the temperature-independent emission wavelength and the long emission lifetime of longer than several μsec. It is considered that these rare-earth-doped GaN layers are applicable to the visible wavelength region fluorescence substances. Furthermore, room temperature ferromagnetic characteristics were observed. The extension to the spintronics devices controlling the interaction between light emission and magnetic field is also interesting.