Structural Properties and Size-control of Visible Photoluminescent Porous Silicon

本研究的目的是寻找具有恒定尺寸分布的剩余硅的多孔硅(PS)层的合适制备条件，并结合光致发光性质讨论p+PS和n+PS层的共同结构特征，包括发射件及其形貌和结晶度。用X射线多晶衍射仪为主，辅以电子衍射仪、扫描电子显微镜和透射电子显微镜研究了低阻比小于0.02OmeGAcm的重掺杂p型和n型硅片上形成的PS层。主要实验结果如下：p+PS层从上表面到下表面呈直径大于10 nm的线状或分支结构。通过控制制备条件，很容易得到尺寸分布均匀的p+PS层。PS层表现出比沿…的Si子态稍大的晶格间距更多垂直于曲面的e方向。用X射线双晶衍射仪测量p+PS层的X射线衍射峰，表明p+PS层的结晶度与Si衬底相同。在室温下，在He-Cd激光照射下表现出强烈光致发光的PS层不是非晶态的，而是结晶的，可见光致发光与PS层表面附近的微结构密切相关，这种微结构表现为海绵状结构，由大量尺寸为几纳米的硅微晶组成。反之，在较大角度范围内，n+PS层的结晶度低于p+PS层，这可能是由于PS层的纳米结构发生了一些改变。研究还发现，n+PS层由几个与阳极氧化过程相关的层状孔结构组成，卤素灯照明非常有效地形成了这种海绵状结构，在PS层的顶部附近可以发出可见的光致发光。综上所述，可见光发射仅来自具有海绵状结构的PS层，该海绵状结构由大量尺寸为几纳米的硅部分组成，光致发光可能是由于这种三维结构中的载流子限制。微晶尺寸与光致发光峰位或蓝移之间的关系的详细研究目前正在进行中。较少

The purposes of this study are to find suitable preparation conditions for porous silicon (PS) layrs having a constant size-distribution of residual Si parts, and to discuss common structural features including emitting parts and their morphology and crystallinity for the p+PS and n+ PS layrs with reference to photoluminescent natures. The PS layrs, formed on heavily doped p-type and n-type silicon wafers of low resistivi less than 0.02OMEGAcm, have been investigated by mainly X-ray multi-crystal diffractometry, supplemented with electron diffraction and scanning electron microscopy and transmission electron microscopy. Main experimental results are as follow : The p+ PS layr presents a wirelike or branched structure of more than 10nm in diameter from the top surface to the bottom part of the PS layr. It was easy to get p+ PS layrs with a constant size-distribution by controlling preparation conditions. The PS layr exibits a slightly larger lattice spacing than the si substate along th … More e direction normal to the surface. The p+ PS layr shows a sharp peak on X-ray diffraction profile measured by X-ray double-crystal diffractometer, indicating that the p+ PS exhibits the same crystallinity as that of the Si substrate. It was also shown that PS layrs which exhibit intensive photoluminescence under He-Cd laser illumination at room temperature are not amorphous, but crystalline, and that the visible photoluminescence is strongly related to the microstructure of PS layr near the surface that shows a spongelike structure consisting of a large number of silicon crystallites of few nm's in size. On the contrary, the n+ PS layr always shows broad diffuse scattering under severl coherent peaks for the n+ PS layr in a large angular range, indicating that the crystallinity of the n+ PS layrs is inferior to that of the p+ PS layrs, probably due to some modifications of the nanostructure of PS layr. It was also found that the n+ PS layrs are composed of several layred pore-structures which are associated with anodization processes, and that halogen-lamp illumination was very effective in forming such a spongelike structure which can emit visible photoluminescence near the top surfaces of the PS layrs.In conclusion, we would like to say that visible light emission comes from only the PS layr that has a spongelike structure consisting of a large number of silicon parts of few nm's in size, and that photoluminescence is probably due to charge carrier confinement in such three dimensional structure. Detailed studies on the correlation between microcrystallite size and photoluminescence peak position or blueshift are now in grogress. Less