Fabrication and characterization of porous silicon layers for applications in optoelectronics

In the present paper, several samples of porous silicon monolayers and multilayers were prepared at different anodization conditions with fixed HF concentration. The room temperature photoluminescence wavelength observed to be increased with increased etching time and current density respectively. By Raman measurement it has been observed that as the size of silicon crystallites decreased with increased etching time, the silicon optical phonon line shifted somewhat to lower frequency from 520.5 cm⁻¹ and became broader asymmetrically. The surface roughness and pyramid like hillocks surface was confirmed by AFM measurement. In SEM images, the porous silicon layers were clearly observed by white and black strips. It was also observed that the reflectivity increased as the number of porous silicon layers was increased.     

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.     

激光诱导多孔硅晶格畸变的Raman光谱和光致发光谱研究

研究了掺钛水热法制备多孔硅的Raman光谱和光致发光谱.实验发现,当激光功率较低时,多孔硅的Raman光谱在略低于520cm^-1附近表现为一锐的单峰,和晶体硅的Raman光谱类似.随激光功率增大,该单峰向低波数移动,Raman和光致发光峰的强度与激光强度的一次方成正比.当激光功率增大到一定值时,该单峰分裂成两个Raman峰,光致发光谱的强度突然增大,与激光强度之间不再满足一次方的关系,位于低波数一侧的Raman峰随激光功率增大进一步向低波数移动.多孔硅Raman光谱随激光功率的变化是 关键词： 多孔硅 Raman光谱 光致发光     

Photoacoustic investigations of the optical absorption spectra of porous silicon layers on a silicon backing

This paper presents a series of experimental photoacoustic spectra of porous silicon layers on crystalline silicon and their numerical analysis performed in the proposed two-layer model. The goal of the analysis was to calculate the optical absorption spectra of porous silicon from the photoacoustic spectra of porous silicon layers on a silicon background. The experimental character of the observed absorption band associated with the porous silicon was revealed. This is the first attempt at a theoretical interpretation of the photoacoustic spectra of porous silicon on a silicon backing.     

Efficient luminescence from porous silicon

Photoluminescence measurements are carried out on porous silicon layers. We show the enhancement and stabilization of the luminescence when depositing a silicon nitride layer on top of porous layers.We also demonstrate that direct- and remote-plasma nitridation are good ways to reduce the ageing effect of porous silicon layers due to a passivation of dangling bonds.     

多孔硅银淀积表面RhB染料分子的表面增强Raman散射

我们采用多孔硅和多孔硅银淀积表面作为衬底研究了ＲｈＢ染料分子的表面增强Ｒａ ｍａｎ散射。在多孔硅表面,ＲｈＢ染料分子的Ｒａｍａｎ散射有大约１０倍的表面增强效果;而在多孔硅的银淀积表面,表现出超过１０４表面增强。通过多孔硅表面银颗粒对ＲｈＢ染料分子荧光的抑制和对Ｒａｍａｎ散射的表面增强,我们获得了谱峰清晰的ＲｈＢ染料分子Ｒａｍａｎ散射谱     

Study of porous silicon structure by Raman scattering

In this paper, the effect of etching time on light emitting porous silicon has been studied by using Raman scattering. Enhancement of Raman intensity by increasing the porosity is observed. Also there is a red shift, about 4 cm⁻¹, from the Raman peak of crystalline silicon to that of porous silicon. The phonon confinement model suggests the existence of spherical nanocrystalline silicon with diameter around 7 nm. But SEM images show that the samples have a sheetlike structure that confines phonons in one dimension. This should not cause any shift in their Raman spectra. It is suggested that the observed Raman peak shift is due to the spherical nanocrystals on the surface of these sheets.     

多孔硅的拉曼光谱研究

本文研究了多孔硅的拉曼光谱随激发激光功率的变化 ,发现当激发光的功率较低时 ,多孔硅的拉曼光谱在 5 2 0cm- 1附近为一单峰。随着激光功率的增加 ,该单峰向低波数移动且半高宽增大 ,当继续增大激光功率时 ,该单峰分裂为双峰 ,位于低波数一侧的拉曼峰随着激光功率的增大而进一步向低波数移动。多孔硅的拉曼光谱随着激光功率的变化是一个可逆的过程。这一结果表明 ,低波数拉曼峰的位置既不能作为多孔硅颗粒尺寸的量度 ,也不能只把低波数的拉曼峰作为多孔硅的特征。我们认为激光诱导多孔硅中LO和TO声子模的简并解除是观察到双峰的主要原因。     

发射可见光多孔硅的拉曼光谱

本文报导了多孔硅的拉曼散射和光致发光的研究。给出了多孔硅的拉曼和光致发光谱之间的对应关系,根据拉曼峰的移动,估算了多孔硅量子线横截面的平均尺度为2.1～4.2nm。     

光学声子色散关系对多孔硅喇曼谱的影响

测量了多孔硅的喇曼光谱,观察到谱峰有明显的红移和非对称性展宽效应。用微晶模型对此现象进行了解释:认为谱峰的这种变化不完全是由尺寸的空间限制效应和多孔硅的应变造成的,更主要的是多孔硅的色散关系发生了变化。采用不同的色散关系对谱峰进行了拟合,发现色散关系对喇曼谱的拟合有较大的影响。     

空间限制与应变对发光多孔硅喇曼光谱的影响

发光多孔硅的喇曼光谱在５２０ｃｍ^－１附近呈现一锐峰，峰位的红移随多孔度的增大而增大采用微晶模型拟合喇曼谱的线形，发现除了光学声子的空间限制效应，硅单晶的应变对峰位的移动也有显著贡献。通过谱形的拟合估算了硅微粒的应变，与已报道的Ｘ射线衍射结果相一致。在多孔硅的喇曼光诸中没有观察到起源于非晶硅的光散射信号。 关键词：     

Enhanced Raman scattering in multilayer structures of porous silicon

Multiple enhancement of the Raman scattering efficiency is observed in porous‐silicon‐based one‐dimensional photonic bandgap (PBG) structures with tunable reflection and dispersion under excitation at 1.06 µm. The experimental results are explained as being due to the resonant increase in the effective Raman susceptibility at light wavelengths close to the PBG edges. This effect is discussed in view of possible applications in the Raman spectroscopy of molecules embedded in porous media as well as in the Raman laser based on silicon. Copyright © 2011 John Wiley & Sons, Ltd.     

Method of porous diamond deposition on porous silicon

In this paper, we discuss the experimental results of the fabrication of porous diamond/porous silicon and porous diamond structures by chemical vapor deposition of diamond over a skeleton of porous silicon, replicating the porous surface geometry around the Si pores and also creating new porous diamond structures. Scanning electron microscopy (SEM) revealed that the diamond nuclei are deposited on the top of the porous silicon skeleton, forming isolated grains in the first nucleation stages, and then growing like the usual structure of most ceramic materials, making a self-sustained porous diamond structure. Raman spectroscopy revealed that the diamond films are of good quality, close to that of diamond films grown on crystalline silicon.     

Anodic oxidation of porous silicon bilayers

This paper focuses on the study of the effect of anodic oxidation in porous silicon bilayers composed of two porous layers of different porosities. The order of the two types of layers has been alternated, and the thicknesses and refractive indices have been optically characterized by Fourier transform infrared spectroscopy. The results show that the refractive index of anodic oxidized porous silicon is reduced significantly with respect to just formed porous silicon. It is also observed that the quality of the oxidation is related to the porosity of the inner porous layer of the silicon bilayer structure. This effect is interpreted in terms of quantum size effects.     

Study on structural properties of epitaxial silicon films on annealed double layer porous silicon

In this paper, epitaxial silicon films were grown on annealed double layer porous silicon by LPCVD. The evolvement of the double layer porous silicon before and after thermal annealing was investigated by scanning electron microscope. X-ray diffraction and Raman spectroscopy were used to investigate the structural properties of the epitaxial silicon thin films grown at different temperature and different pressure. The results show that the surface of the low-porosity layer becomes smooth and there are just few silicon-bridges connecting the porous layer and the substrate wafer. The qualities of the epitaxial silicon thin films become better along with increasing deposition temperature. All of the Raman peaks of silicon films with different deposition pressure are situated at 521 cm⁻¹ under the deposition temperature of 1100 °C, and the Raman intensity of the silicon film deposited at 100 Pa is much closer to that of the monocrystalline silicon wafer. The epitaxial silicon films are all (4 0 0)-oriented and (4 0 0) peak of silicon film deposited at 100 Pa is more symmetric.     

Comparative investigation of photoluminescence of silicon wire structures and silicon oxide films

Photoluminescence spectra and their dependence on temperature as well as Raman scattering spectra and Atomic Force Microscopy investigations have been used to study the peculiarities of the red photoluminescence band in low-dimensional Si structures, such as porous silicon and silicon oxide films. It has been shown that the red photoluminescence band of porous silicon is complex and can be decomposed into two elementary bands. It was discovered that elementary band intensities depend very much on surface morphology of porous silicon. The same positions of the photoluminescence bands are also observed in silicon oxide films for different oxide composition. Comparative investigation of the PL temperature dependences in porous silicon and silicon oxide films indicates that silicon-oxide defect related mechanisms of some elementary photoluminescence bands are involved.     

Heterojunction solar cells produced by porous silicon layer transfer technology

In this paper, we present the result of heterojunction solar cells based on porous silicon layer transfer technology. a-Si/c-Si structured solar cells were prepared in which the c-Si was deposited on annealed double-layer porous silicon by low-pressure chemical vapor deposition. The structural properties and the evolvement of the double-layer porous silicon before and after thermal annealing were investigated by scanning electron microscopy. X-ray diffraction, Raman spectroscopy and a microwave photoconductive decay method were used to investigate the properties of the epitaxial silicon thin films deposited at different pressures. And, the influence of the deposition pressure on the properties of the c-silicon thin films was investigated. The spectral responses of the cells were studied by a quantum efficiency test. The results show that the epitaxial silicon thin film deposited at 100 Pa has better carrier lifetime and better spectral response. Furthermore, the Raman peak intensity of the silicon film prepared at 100 Pa is much closer to that of a monocrystalline silicon wafer. A simple solar cell structure without any light-trapping features showed an efficiency of up to 10.1 %.     

Electrochemical etching of n-type 15R-SiC and 6H-SiC without UV illumination

We report the formation of porous n-type 15R- and 6H-SiC and analyze the porous layers using scanning electron microscopy, Raman scattering and X-ray diffraction (XRD). The crystal structures and the preparation conditions of porous SiC are shown to have an effect on the structural and electrical properties of the material obtained. Raman spectra of porous SiC layers have shown some specific features compared with those of bulk SiC. For the porous 15R-SiC, the semi-cylindrical structure of the porous network has been observed and the porosity is about 66%.     

拉曼光谱法计算多孔硅样品的温度

利用457.5nm固体激光器作为激发光源，得到了在不同功率激发下的多孔硅样品的拉曼光谱以及一些谱峰参数随功率的变化关系. 在从前的理论研究中，认为是由于激光功率的增大导致样品局域温度升高，从而使样品局域粒径变小，并由此引起了一系列谱峰参数的变化. 分别由520cm^-1和300cm^-1附近得到的随功率变化的拉曼谱图，详细讨论并计算了激光功率对多孔硅样品局域温度的定量影响，为拉曼光谱用于样品温度的定量测量奠定了实验基础. 关键词： 拉曼光谱 多孔硅 激光功率 样品温度     

多孔硅拉曼光谱的研究

采用电化学腐蚀的方法制备多孔硅。对不同实验条件下所得到的多孔硅的拉曼光谱进行了分析，确认多孔硅是具有纳米晶结构特征的材料，肯定了量子限制效应在多孔硅光致发光中的作用。