论文标题:硅纳米孔柱阵列及其硫化镉纳米复合体系的光学特性研究
论文作者
论文导师 李新建,论文学位 硕士,论文专业 光学
论文单位 郑州大学,点击次数 707,论文页数 101页File Size9867k
2005-05-01论文网 http://www.lw23.com/lunwen_242627/
Si-NPA; CdS/Si-NPA; Optical constant; hydrothermal etching; Kramers-Kronig transformation; photoluminescence; electronic structure
对硅纳米材料及硅基纳米复合体系的构建技术、物理特性尤其是光电特性的研究具有重要的科学价值和实际意义。本论文首先对课题组采用水热技术制备出的、一种具有三重层次结构的硅纳米/微米结构复合体系,即硅纳米孔柱阵列(Si-NPA),的光反射吸收、光致发光、介电特性、电子结构特征等物理性能进行了系统地详细研究;并通过微乳匀胶技术和原位多相化学反应技术实现了Ⅱ-Ⅵ族化合物半导体硫化镉在Si-NPA上的位置选择性沉积,获得了四类具有不同结构特征的、大面积均匀的、规则的半导体异质结阵列体系(CdS/Si-NPA),并对它们的光学性能进行了讨论。对上述硅纳米材料与硅基纳米复合体系的物理性能研究与内在机制的探索,为它们在光电材料、发光二极管阵列以及太阳电池等领域的可能应用奠定了理论基础。主要研究内容包括以下两个部分: 1.Si-NPA的光致发光、反射吸收、光学常数等光学性能及电子结构特征的研究 采用高压水热腐蚀技术、以单晶硅为基材制备出一种大面积均整的、具有三重层次结构的硅纳米/微米结构复合体系—硅纳米孔柱阵列(Silicon Nanoporous Pillar Array, Si-NPA)。首先借助于积分反射谱测量及有效介质近
It is important in basic scientific research and applications that fabrication and physical properties, especially photoelectronic properties of silicon nanomaterials and silicon-based nanocomposite systems are studied. In this paper, silicon nanoporous pillar array (Si-NPA), a typical micron/nanometer composite system with clear hierarchical structures, was prepared by a novel hydrothermal technique. Its physical properties-such as reflectivity, absorption, photoluminescence, dielectric property, electrical structure property, and so on.-was studied systematically. Then ultra thin films of CdS were deposited on Si-NPA by using spin-coating technique and a simple chemical polyphase reaction, and four kinds of uniformed CdS/Si-NPA heterojunctions with different structures were obtained. Similarly to the above Si-NPA, varied physical properties for the heterojunctions materials were also systematically studied and discussed. On this basis, the inherent mechanisms were explored on the Si-NPA and CdS/Si-NPA, which will establish a solid foundation for the applications in many fields such as photoelectric materials, heterojunction diode arrays and silicon-based solar cells. The main points in this paper are as follows:1. Study on the properties of optics and electrics for Si-NPASilicon nanoporous pillar array (Si-NPA) was prepared by using a novel hydrothermal technique. Porosity-an important structural parameter with closed correlation to the properties of physics, chemistry and dynam of Si-NPA-was calculated by the use of reflectivity spectrum and a theory model of effective-medium approximation, which was a novel method presented by us on calculating porosity ofporous materials. At the same time, some optical constants about Si-NPA, such as complex refractivity, complex dielectric function and absorption coefficient, were obtained by reflectivity spectrum and Kramers-Kroning transformation theory. The electrical structural properties of Si-NPA were also studied by the help of the obtained optical constants. The study on the dispersive relation of optics showed that peaks of theimagination of dielectric constant (at 4.05 eV and 5.0 eV respectively in ￡2(co)) were originated from the two peaks located at 3.4 eV and 4.6 eV in ￡2{co) spectrum ofsc-Si, only by the blue-shifts of 0.65 eV and 0.4 eV compared to the latter. The obtained results were well agreed with the theoretical calculation according to the quantum confinement effect. Furthermore, the analysis to the electrical structure by the help of Tauc"s theory at absorption edge showed that the structure of Si-NPA has transformed from single-conduction band structure into direct band-width structure with two-conduction bands. The structure of two-band gaps at 2.01ev and 3.06ev was also agreed with photolutninescence peaks, which could further prove the decisive role of quantum confinement effect on the physical properties of Si-NPA.2. The preparation and optical properties of CdS/Si-NPA nanometercomposite system(1) wc-CdS was synthesized by microemulsion method, and then a composite thin film was fabricated by spin-coating nanocrystal CdS onto Si-NPA. The experimental results indicated that the photoluminescence intensity of CdS/Si-NPA composite enhanced by one magnitude compared to single Si-NPA, and only a narrow bule PL peak appeared for CdS/NPA system. (2) Hiring Si-NPA as templates, three kinds of CdS/Si-NPA nanocomposites were prepared by in situ synthesis of CdS via a simple polyphased reaction on the Si-NPA. The first type of CdS/Si-NPA composite film has a composite structure of ring-cluster, which means that CdS nanorings appeared around every silicon pillar"s bottom and CdS clusters appeared on the top. The second type was obtained at the same experimental conditions, only by altering CdCl2 aqueous solutionto alcohol solution. CdS nanofilm was uniformly coated on the surface of the substrate, forming a uniform cap-like structure on every silicon"s pillar. The third type CdS/Si-NPA film was prepared by using ultraviolet lamp to irradiate at certain energy. CdS nanopoles grew along silicon pillars. Due to the different conductive types between CdS and Si-NPA materials, the prepared CdS/Si-NPA of the latter two types could be belonged to a good kind of nanometer composite system of silicon-based heterojunction semiconductor. The results of PL showed that the PL peak at ~ 495 nm appeared, which comes from photoluminescence of CdS nanocrystalline, meanwhile double red peaks of substrates of the first type film still existed. Besides, the PL peak positions and intensities of the second and third types were same, but their main PL peak has a 20 nm blue shift compared to the PL peak of Si-NPA substrate, which may be caused by the change of the effective dielectric constant during the formation of CdS/Si-NPA structure.
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