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

1. (1)掺硅SiO_2玻璃：通过溅射法制备的掺硅玻璃经过热处理后发出强烈的红光。脉冲EL的衰减时间常数一般在0.4msec左右，表明复合过程相当缓慢。(2) Si超细颗粒：在氢气中制备的超细颗粒在不进行氧化过程的情况下表现出较强的可见光PL。同样的粒子被Si衬底和ITO玻璃夹在一起，也可以观察到EL。(3)含氧硅纳米结构：在含氧大气中通过气体蒸发制备的链状超细颗粒组成的硅纳米结构具有较强的蓝光发射能力。这些结构的化学成分是SiO_X。(4)多孔硅：多孔硅内部的硅纳米结构实际上是由纳米尺寸的硅超细颗粒组成的。当阳极氧化温度为0 ~ 40℃时，多孔硅在室温下的发射强度提高了约4个数量级。在200K左右，发光强度与阳极氧化温度无关，几乎达到相同的水平，说明发光是由非辐射复合速度控制，而不是由发射中心的密度控制。发射机制不同类型的硅纳米结构的红到黄的发射很可能是由于相同的来源，因为发射强度的温度依赖性非常相似。虽然激发光的吸收过程可能与量子尺寸效应相关的吸收边蓝移有关，但发射来自位于Si超细颗粒表面/界面附近的发射中心。发现蓝光发射与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.