Optical Properties of Si Ultrafine Particles and the Applications to Light-Emitting Devices

1.不同类型硅纳米结构的可见光发射(1)掺硅SiO_2玻璃：采用溅射法制备的掺硅玻璃在热处理后表现出较强的红色发光。脉冲电致发光的衰减时间常数典型地约为0.4毫秒，表明复合过程相当缓慢。(2)硅超细颗粒：在氢气中制备的超细颗粒在没有氧化过程的情况下表现出很强的可见光发光。含氧硅纳米结构：由气体在含氧大气中蒸发制备的链状超细颗粒组成的硅纳米结构显示出很强的蓝光发射。这些结构的化学成分是SiO_x。(4)多孔硅：多孔硅中的硅纳米结构实际上是由纳米级的硅超微粒组成的。当阳极氧化温度从0ﾟC改变到40ﾟC时，多孔硅在室温下的发光强度增加了约4个数量级，发光强度在200K左右变得几乎相同，这表明发光是由非辐射复合速度控制的，而不是由发射中心的密度控制的。不同类型的硅纳米结构的红光到黄光的发射很可能是由同一来源引起的，因为发射强度与温度的关系非常相似。虽然激发光的吸收过程可能与量子尺寸效应引起的吸收边蓝移有关，但发射来自位于硅超微粒表面/界面附近的发射中心，蓝光发射与SiO_X内部的缺氧态有关。

1. Visuble light emission from various types of Si nanostructures(1) Si-doped SiO_2 glass : The Si-doped glass prepared by the sputtering method showed strong red luminescence after the heattreatment. The decay time-constant of pulsed EL was typecally about 0.4msec indicating that the recombination process is rather slow.(2) Si ultrafine particles : The ultrafine particles prepared in hydrogen showed strong visible light PL without making oxidation procedure. EL was also observed from the same particles sandwiched by a Si substrate and an ITO glass.(3) Oxygen-containing Si nanostructres : Si nanostructures composed of chained ultrafine particles prepared by the gas evaporation in oxygen-containing atmospohere showed strong blue light emission. The chemical composition of these structures were found to be SiO_X.(4) Porous Si : The Si nanostructure within the porous Si was actually composed of Si ultrafine particles with nm size. The emission intensity from the porous Si at the room temperature increased about four orders of magnitude by changing the anodization temperature from 0ﾟC to 40ﾟC.The luminescence intensity becomes almost the same level at about 200K independent upon the anodization temperature, indicating that the emission is controlled by the nonradiative recombination velocity and not by the density of the emission centers.2. Emission mechanismsRed-to-yellow emissions from various types of Si nanostructures are most likely due to the same origin because of the quite similar temperature dependence of the emission intensity. Although the absorption process of the excitation light is likely to be related to the blue shift of the absorption edge associated with the quantum size effect, the emission comes from the emission centers located near the surface/interface of Si ultrafine particles.The blue light emission was found to be related to the oxygen-deficient states within SiO_X.