摘要
低维半导体的研究是现在材料领域发展最快、最吸引人的，并有重要的技术应用前景。多孔硅(porous silicon,PS)以其简单的制备方法、复杂的微结构特征和较高的光致发光效率吸引了众多研究者的目光。自1990年Canham发现多孔硅室温下发射可见光的现象以后，人们对多孔硅的形成机理、发光机制以及技术上的应用做了很多有意义的工作。对于多孔硅的基础性研究主要在于其形成机理、微观结构及其化学组成、发光特性以及发光机制的研究。对于多孔硅是怎样形成的问题，现在主要有Beale模型、扩散限制模型和量子限制模型进行解释。许多实验结果显示多孔硅中含有大量按一定尺寸分布的纳米硅粒和纳米硅线，结构比较复杂，而且多孔硅基本保留了单晶硅的结构特征，其中的纳米硅为有序单晶。氢、氟、碳、氧这四种元素是存在于多孔硅中最常见的组成元素并已被实验所证实。对于多孔硅，人们最感兴趣的是它的光学性质，尤其是它的发光特性。经过阳极化处理后得到的多孔硅能发射较强的近红外、可见和近紫外光，而人们最关注的是PS在整个可见光波段(S band)的发光。多年来，人们对多孔硅发光机理一直进行着坚持不懈的探讨和研究，提出了许多种解释多孔硅层(PSL)发光的模型，典型的有下列几种：量子限制模型、硅-氢键或多硅烷(polysilanes)的发光、硅氧烯及其衍生物的发光、表面态模型和量子限制-发光中心模型。对多孔硅进行研究的主要目的在于获得硅发光集成装置，在不同的领域也进行了其他的应用研究。目前多孔硅的应用研究体现在三个方向：光电子器件，光学器件和传感器件。在多孔硅的实用研究中，也发现了许多需要克服的问题，例如多孔硅的发光稳定性差、器件的寿命短，发光效率低以及结构的机械强度低等。
I 已有的研究表明，多孔硅的微观结构收如孔隙率、膜厚、孔径等）
I 及其发光性质取决于其制备工艺和条件，所以对于多孔硅制备方法和
Z 条件的研究是促进多孔硅实现应用的基本途径。目前，多孔硅的制备
【方法已有许多种。本文首先通过电化学方法、光化学方法和化学万法
I 分别制备出了室温下在可见光区发射光荣光的多孔硅，通过对实验装
1 置、制备条件、样品的成膜过程及其光致发光闪L）光谱的比较，分
【析解释了其成膜机理和PL光谱的特点；认为虽然这三种方法都可以制
I 备出室温下发光的多孔硅，但相比较而言，通过电化学方法制备的样
I 品最均匀，实验的可重复性较强，因而是被普遍采用的一种方法。另
【外在多孔硅的成膜过程中；自由载流子起着至关重要的作用。
【在实验中，不同实验条件下制备的多孔硅的光致发光特性（PL）
I 是不同的；这是许多研究结果和理论分析发生分歧的主要原因。在第
Z 三章中；通过对比，分析了电流密度、阳极化时间、溶液浓度以及自
I 然氧化时间对多孔硅光致发光光谱的影响，认为在一定的范围内，多
I 孔硅的发光峰位会随电流密度的增大而蓝移，要获得较强的发光，需
Z 要选择合适的电流密度；随着腐蚀时间的延长，多孔硅的发光峰位会
I 发生蓝移；当＊F酸的浓度较小q：1）时，峰位随浓度的增大表现为向
I 低能移动；而当＊F酸的浓度较大河山时，峰位随浓度的增大则表现
Z 为移向高能；多孔硅在空气中自然氧化；其发光峰位发生蓝移，而强
I 度随放置时间的延长而降低。以上实验现象 都可以通过量子限制模
【型和发先中。模型得到解释，但在9孔硅61发光？，也不能否定a－H
I 键和表面缺陷在发光中的作用。
【目前，多孔硅的发光机制仍是人们研究的主要问题之一，对于其
【应用研究也许要经历比较长的时间，但随着研究的不断深入和各种测
【试技术的发展，作为微电子主要材料的硅也必将在光电子领域展示其
【迷人的应用前景。
The study of low dimension semiconductor is a very active field of research and has important technical applied promise. Simply prepared method, complex constructure characteristics and higher photoluminescence efficiency in porous silicon have attracted a lot of attention of investigators. Since Canham detected that porous silicon can emit visible light at room temperature in 1990, a lot of significative work have been done on its formation and radiation mechanism and the possibility of technical applied. Beale model, diffusion confinement model and quantum confinement effect model are used to explain how porous silicon comes into being. Many experimental results reveal that a great deal of nanocrystal silicon particles and cylinders with certain size distribution in porous silicon has complex constructure and hold the character of monocrystaline silicon, in which nanosilicon is order monocrystaline. Hydrogen, fluorin, carbon and oxygen are familiar elements in PS confirmed by different experiments. Porous
silicon can radiate strong near infrared, visible and near ultraviolet light, but whole S band is most interested in. PS radiation mechanism has been discussed and investigated for many years and many theoretical models have been proposed to describe photoluminescence in porous silicon, for instance quantum confinement effect model, polysilanes model, siloxen and its derivant, surfacial states model and quantum confinement-light center model etc. In addition, study status of PS at present is addressed and applied problems in some fields are analyzed in this section.
On the experimental side, research suggests that microstructure of PS (porosity, film thickness, aperture etc.) and its radiative properties are determined by prepared technics and conditions, so it is fundamental
approach that investigate prepared method and conditions to promote the development of PS applied. At first, we prepared PS samples at room temperature by electrochemical method, photochemical method and pure chemical method and measured its PL spectrum separately. By compared setup, conditions, formed process and their PL spectra, their formed mechanism and PL spectrum characteristics are analyzed and explained. These three methods all can prepare PS, which radiate visible light at room temperature, but samples prepared by electrochemical method is uniformity relatively and the experiment has more repeatability, so it is extensively applied to prepare PS. Otherwise, free carriers play an important role in the process of film forming.
Many experimental results and theoretical analysis diverge mostly because different conditions can seriously affect PL properties in porous silicon. In the third chapter, the influence of current density, solution concentration, erosion time and aging in ambient air on the PL spectra of PS suggests that peak would blue shift with current density increasing, and with erosion time and aging time prolonging; With the increasing of solution concentration, peaks would red shift when solution concentration less than 1:1 but blue shift when solution concentration greater than 1:1. Above phenomena can be explained by quantum confinement and light center model, but do not deny the action of Si-H bonding and defect on the surface in the process of photoluminescence.
At present, radiation mechanism is still one of the primary problems in the study of PS. With the development of study and various measurement techniques, Si as major material in microelectronics field shows wide promise in photoelectronics field.
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