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6.4 V/μm的电场电子发射阈值。为了有效降低场发射隧道势垒高度，在GaN表面形成薄AlN层，实现阈值场的降低：电子亲和降低0.8 eV。为了控制晶粒结构和改善发射特性，在硅衬底上生长GaN，并在SiO_2薄层上生长。在阈值场低至1.25 V/μm的条件下，GaN纳米棒的场电子发射得到了极大的改善，在2.5 V/μm下的发射电流密度高达2.5 mA/cm^2。氮化镓纳米棒具有与衬底较强的附着力，在场发射电子器件中具有广阔的应用前景。稀土掺杂的GaN、GaEuN、GaGdN和GaDyN在可见光区获得了强的尖锐光致发光。结果表明，这些发光是由稀土原子的原子能级跃迁引起的，因为它们的发射波长与温度无关，且发射寿命超过几μsec。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，还观察了材料的室温铁磁特性。对自旋电子学器件控制光发射与磁场相互作用的扩展也很有趣。

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.