多孔硅光致发光峰半峰全宽的压缩

硅发光对于在单一硅片上实现光电集成是至关重要的.目前已有的使硅产生发光的方法有:掺杂深能级杂质、掺稀土离子、多孔硅、纳米硅以及Si/SiO₂超晶格.声空化所引发的特殊的物理、化学环境为制备光致发光多孔硅薄膜提供了一条重要的途径.实验表明,声化学处理对于改善多孔硅的微结构,提高发光效率和发光稳定性都是一项非常有效的技术.超声波加强阳极电化学腐蚀制备发光多孔硅薄膜,比目前通用的常规方法制备的样品显示出更优良的性质.这种超声波的化学效应源于声空化,即腐蚀液中气泡的形成、生长和急剧崩溃.在多孔硅的腐蚀过程中,由于超声波的作用增加了孔中氢气泡的逸出比率和塌缩,有利于孔沿垂直方向的腐蚀,使多孔硅光致发光峰的半峰全宽压缩到了3.8nm.     

发光多孔硅表面微结构及其晶格畸变的实验研究

用电化学方法制备了不发光多孔硅和发光多孔硅,用X射线双晶衍射对两类多孔硅表面进行了微结构分析和晶体质量表征,实验表明两类多孔硅的微结构间存在着很大差别。不发光多孔硅表面对X射线的双晶衍射摇摆曲线可解叠成两个峰,它们分别来自样品多孔层和单晶硅衬底,而发光多孔硅对X射线的双晶衍射摇摆曲线呈高斯对称分布,不可解叠。发光多孔硅比不发光多孔硅表面晶体质量差,且电化学腐蚀越严重,表面晶体质量下降也越严重。     

多孔硅发光与量子尺寸效应的实验研究

利用电化学阳极腐蚀的方法制备了多孔硅膜,实验发现多孔硅膜为多层结构,表面层为纳米结构,其余为微米结构,多孔硅的物理及化学结构的研究表明多孔硅是一种表面上含硅、氧、氢、氟元素组成的化合物包覆着的纳米晶硅粒和微米硅丝.多孔硅的发光主要来自表面纳米结构层,亚微米结构层并未见发光,从实验上证实了多孔硅的发光与量子尺寸效应紧密关联.     

多孔硅的微结构与发光特性研究

利用原子力显微镜（AFM）和光致荧光（PL）光谱对一系列直流腐蚀和脉冲腐蚀的多孔硅的微结构及发光特性进行了对比研究．表面和侧面的AFM结果表明，多孔硅表面呈“小山”状，有许多小的、突出的硅颗粒．在相同的腐蚀条件（等效）下，脉冲腐蚀的样品表面Si颗粒更加尖锐、突出，侧面的线状结构更明显，多孔硅层更厚．对应的PL谱，脉冲腐蚀的样品发光更强．量子限制效应的理论可以比较成功地解释这个结果 关键词：     

少子寿命和表面形貌与多孔硅发光性能的关系

研究了不同时间腐蚀的多孔硅的光致发光性能与多孔硅的表面形貌和少子寿命之间的关系。结果表明,多孔硅的发光来自与氧空位有关的缺陷,而多孔硅表面的氢原子能够钝化多孔硅表面的非辐射中心从而提高多孔硅的发光效率。多孔硅的空隙度随腐蚀时间的延长而增大,这也导致了多孔硅的少子寿命的降低,从而造成多孔硅的光致发光效率随多孔硅空隙度的增大以及少子寿命的降低而提高。另外,原子力显微照片表明长时间的腐蚀使多孔硅表面层被化学腐蚀,从而降低了多孔硅表面的粗糙度。     

多孔硅的光致发光和红外吸收光谱研究

用电化学腐蚀法制备出多孔硅系列样品.室温下具有明亮可见的光致发光.增大电解电流或延长腐蚀时间,发光光谱明显地“蓝移”;提高样品测量温度,发光光谱也明显地“蓝移”。红外吸收光谱表明多孔硅中除了硅丝骨架以外,还含有H、F及O等元素,随着腐蚀时间的增加,F和O原子的相对含量增加.实验结果表明,多孔硅在可见光区的发光现象是一种量子尺寸效应.     

掺钛化学腐蚀法制备发光稳定的多孔硅

本文采用掺钛化学腐蚀法制备出了发光稳定性和均匀性都较好的多孔硅 (PS)。存放和退火试验表明 ,光致发光 (PL)谱峰位不蓝移 ,强度不衰减。多孔硅发光稳定性的提高归因于制备过程中样品表面原位氧和钛的钝化。钛的浓度和腐蚀时间对PL强度有明显影响 ,最佳钛浓度约为 0 0 8mol·L- 1 ,最佳腐蚀时间约为 2 0min。掺钛化学腐蚀法制备的PS的光激发过程符合量子限域机制 ,而其PL过程却与量子限域模型不符 ,这表明其光发射过程不是带 带直接跃迁产生的 ,即存在一个表面态     

硫酸中多气泡声致发光光谱

非线性声波方程与气泡脉动方程联立, 可以描述声空化云中的声场以及任何一个气泡的脉动过程,为数值计算空化场问题提供了理论框架.计算的声压分布变化可以用来计算单气泡动力学,了解任何位置处气泡发光过程以及气泡内气体温度和压强变化等. 对浓硫酸中氙气泡空化云的计算定性符合实验观测, 只有钠原子线谱的计算结果相比实验观测有些出入.     

发光不衰减的多孔硅

用一种新的方法制备出了具有不同衰减的光致发光特性的多孔硅。如此制备的多孔硅新鲜样品,其发光峰位强度比普通多孔硅高２￣２．５倍,将样品在室温下暴露于空气中,其发光强度在前４个月中单调增加,然后达到饱和。在随后的８个月中,没有观察到发光衰减,发光峰位也没有发生变化,这种发光稳定性被归因子于多孔硅表面所形成的稳定的Ｆｅ－Ｓｉ键。文章探讨了发光不衰减、峰位不蓝移的机理,并为多孔硅发光的量子限域模型提供了强     

多孔硅的后处理及其发光特性

采用一种新颖而简便的方法,改善多孔硅的发光特性。该方法包括酸处理和阴极还原两步。实验证明通过对多孔硅进行酸处理,能有效提高多孔硅的发光强度;通过对多孔硅进行阴极还原处理,能明显改善多孔硅的发光稳定性,而且发光强度也得到了提高。综合酸处理和阴极还原两技术的特点,对所制备的多孔硅立即先进行酸处理,然后再对其进行阴极还原处理,结果表明该方法能较好地提高多孔硅的发光效率和发光稳定性。而且还对其发光机制进行了探讨。     

A novel method of fabricating porous silicon material: ultrasonically enhanced anodic electrochemical etching

Ultrasonically enhanced anodic electrochemical etching is developed to fabricate luminescent porous silicon (PS) material. The samples prepared by the new etching method exhibit superior characteristics to those prepared by conventional direct current etching. By applying ultrasonically enhanced etching, PS microcavities with much higher quality factors can be fabricated. The improved quality induced by ultrasonic etching can be ascribed to increased rates of escape of hydrogen bubbles and other etched chemical species from the porous silicon pillars' surface. This process will cause the reaction between the etchant and the silicon wafer to proceed more rapidly along the vertical direction in the silicon pores than laterally.     

The effects of chemical etching of porous silicon on Raman spectra

We have investigated the effects of chemical etching on Raman spectra of porous silicon. The as-anodized porous silicon consisted mainly of crystalline silicon, as indicated by the Raman spectra. The background in the spectrum was strong, indicating that the porous silicon surface was rough due to the presence of pores. When chemical etching was performed five times, the Raman spectrum revealed the presence of spherically shaped nanocrystalline silicon whose diameter was around 3.5 nm. Further chemical etching, however, extinguished the nanocrystallites, in addition to smoothing the surface morphology.     

Tunable photoluminescence of porous silicon by liquid crystal infiltration

The photoluminescence (PL) of porous silicon films has been investigated as a function of the amount of liquid crystal molecules that are infiltrated into the constricted geometry of the porous silicon films. A typical nematic liquid crystal 4-pentyl-4′-cyanobiphenyl was employed in our experiment as the filler to modify the PL of porous silicon. It is found that the originally red PL of porous silicon films can be tuned to blue by simply adjusting the amount of liquid crystal molecules in the microchannels of the porous films. The chromaticity coordinates are calculated for the recorded PL spectra. The mechanism of the tunable PL is discussed. Our results have demonstrated that the luminescent properties of porous silicon films can be efficiently tuned by liquid crystal infiltration.     

Porous silicon layers prepared by electrochemical etching for application in silicon thin film solar cells

In this paper, multilayer structures of porous silicon were fabricated by using electrochemical etching and characterized for its optical properties and surface morphology. Samples of monolayer of porous silicon were grown to study the characteristics of porous layer formation with respect to applied current density, etching time and hydrofluoric acid concentrations. Photoluminescence peaks of red emission at wavelength 695 and 650 nm were observed from multilayer porous silicon structures. By atomic force microscopy measurement, hillocks like surface were clearly observed within the host material, which confirmed the formation of pores.     

Laser-induced etching of silicon

Conventional fabrication method of porous silicon is anodisation of single crystal silicon in hydrofluoric acid. In this report, we show that it is possible to fabricate porous silicon by laser-induced etching. An earlier report by us has demonstrated the dependence of porous silicon photoluminescence characteristic on the etching laser wavelength [1]. Here we used 780 nm line from a diode laser as the etching source, and the optimum etching conditions were obtained. A simple model was proposed to explain the etching process. Scanning Electron Microscope (SEM) images of the samples support the proposed process.     

Birefringence and anisotropic optical absorption in porous silicon

The refractive indices and the coefficients of optical absorption by free charge carriers and local vibrations in porous silicon (por-Si) films, comprising nanometer-sized silicon residues (nanocrystals) separated by nanometer-sized pores (nanopores) formed in the course of electrochemical etching of the initial single crystal silicon, have been studied by polarization-resolved IR absorption spectroscopy techniques. It is shown that the birefringence observed in por-Si is related to the anisotropic shapes of nanocrystals and nanopores, while the anisotropy (dichroism) of absorption by the local vibrational modes is determined predominantly by the microrelief of the surface of nanocrystals. It is demonstrated that silicon-hydrogen surface bonds in nanocrystals can be restored by means of selective hydrogen thermodesorption with the formation of a considerable number of H-terminated surface Si-Si dimers.     

High resolution X-ray studies of porous PbTe layers on silicon substrates

The structure of PbTe films after anodic electrochemical etching in Norr electrolyte is studied by high resolution X-ray diffractometry and reflectometry. Lattice defects before and after etching are estimated. The quantitative parameters of the pores are determined. The advantage of the complex application of high resolution X-ray methods for the determination of the real structure of lead-telluride porous films is shown.     

Self detachment of free-standing porous silicon membranes in moderately doped n-type silicon

In this article we describe a reliable etching method to fabricate porous silicon free-standing membranes (FSMs) based on a self detachment of the porous layer in moderately doped n-type silicon substrates. We found that stable growth of smooth and straight pores is restricted to a narrow range of etching conditions and, unlike p-type substrates, the lift-off of the membrane is a self-limited process that does not require a large burst of current. The detachment of the porous membrane is independent of the structure of the already porosified layer, meaning that the average pore diameter can be tuned from nano to macro size within the same membrane. We also demonstrate that, despite their limited thickness, FSMs are quite robust and can sustained further processing. Thus, the etching receipt we are proposing here extends the range of sensors and filters that can be fabricated using porous silicon technology.