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

在金属钼衬底上生长的多晶GaN获得了6.4V/μm的低阈值电场电子发射。为了有效地降低场发射隧道势垒高度，在GaN表面形成了较薄的AlN层，并实现了阈值电场的降低：电子亲和势降低了0.8 eV。为了控制晶体结构和改善发射特性，在具有较薄SiO_2层的Si衬底上生长了GaN。在阈值电场为1.25V/μm的条件下，自组装了GaN纳米棒，在2.5V/μm下的发射电流密度高达2.5 mA/cm~2，与衬底的粘附性很强，可望应用于场发射电子器件。结果表明，这些光发射是由于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，发射寿命长达几μ秒以上。认为这些稀土掺杂GaN层适用于可见光波段的荧光物质。此外，还观察到了室温铁磁特性。控制光发射和磁场之间相互作用的自旋电子学装置的扩展也很有趣。

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.