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

在Mo金属衬底上生长的多晶GaN，获得了6.4V/μm的低阈值场致电子发射。为了有效地降低场发射隧道势垒高度，在GaN表面生长了一层AlN薄膜，实现了阈值场的降低：电子亲合势降低了0.8eV。为了控制晶粒结构，改善发射特性，在Si衬底上生长了一层SiO2薄膜。GaN纳米棒自组装后，场致电子发射性能大大提高，阈值电场低至1.25 V/μm，发射电流密度在2.5 V/μm时高达2.5 mA/cm^2。GaN纳米棒具有与衬底的强粘附特性，有望应用于场发射电子器件。稀土掺杂的GaN，GaEuN，GaGdN和GaDyN在可见光区获得了强的光致发光。结果表明，这些光发射是由于稀土原子的原子能级跃迁，因为发射波长与温度无关，发射寿命长于几微秒。认为这些稀土掺杂GaN层适用于可见波长区域的荧光物质。此外，观察到室温铁磁特性。控制光发射和磁场之间相互作用的自旋电子学器件的扩展也很有趣。

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.