多孔硅PL谱的影响因素分析

通过阳极氧化电化学方法制备了多孔硅,并在室温下对不同条件下制得的多孔硅光致发光谱(PL谱)进行系统的分析.结果表明,随着阳极电流密度、阳极化溶液浓度和时间的增大,多孔硅的PL谱峰将发生"蓝移",并且PL峰强也显著增加,但过大的电流密度、阳极化溶液浓度和时间将导致PL峰强下降.另外,还发现PL谱存在多峰结构,而多孔硅在空气中放置时间的延长将引起其PL的短波峰"蓝移"和强度下降,但对长波峰只引起强度减弱,并不影响其峰位.PL谱的多峰结构可以认为是由于样品中同时存在"树枝"状和"海绵"状两种微观结构所产生的,在这个假设下,用多孔硅氧化后发光中心从硅表面移到二氧化硅层及量子限制模型能够解释上述现象.     

Experimental testing of a random medium optical model of porous silicon for photovoltaic applications

We have developed a model for light propagation in porous silicon (PS) based on the theory of wave propagation in random media. The low porosity case is considered, with silicon being the host material assuming randomly distributed spherical voids as scattering particles. The specular and the diffuse part of the light could be determined and treated separately. The model is applied to the case in which porous silicon would be used as a diffuse back reflector in a thin‐film crystalline silicon solar cell realized in an ultrathin (1–3 μm) epitaxially grown Si layer on PS. Three layer structures (epi/PS/Si) have been fabricated by atmospheric pressure chemical vapor deposition (APCVD) of 150–1000 nm epitaxial silicon layers on silicon wafers of which 150–450 nm of the surface has been electrochemically etched. An excellent agreement is found between the experimentally measured reflection data in the 400–1000 nm wavelength range and those calculated using the proposed model. The values of the layer thickness agree, within a reasonable experimental error, with those obtained independently by cross sectional transmission electron microscopy (XTEM) analysis. This provides an experimental verification of the random medium approach to porous silicon in the low porosity case. The analysis shows that the epitaxial growth process has led to appreciable porosity decrease of an initially high porosity layer from about 60% to 20–30%. Copyright © 2001 John Wiley & Sons, Ltd.     

多孔硅秃腔微结构的AFM和SEM研究

多孔硅微腔是采用交替变化脉冲腐蚀电流密度的方法制成的多孔度周期性变化的多孔硅结构。用原子力显微镜（AFM）和扫描电子显微镜（SEM）对多孔硅微腔的侧向解理的截面进行了观测，得到了不同多孔层及其界面处的图像。微腔截面的扫描电镜图像清楚地显示出第Ⅱ型多孔硅微腔的“三明治”结构，即中心发光层被夹在两个Bragg反射镜之间，这些结果表明结合分子束外延技术和电化学腐蚀方法可以很容易得到多孔硅微腔。     

Self-diffraction in Porous Silicon/PMMA-DR1 Composite Films

Two-layer structure consisting of PS/PMMA-DR1 composite film planar waveguide layer on porous silicon cladding layer was fabricated in our experiment. The induced grating based on the third nonlinear optical properties was formed by interaction of two Nd ： YAG laser beams at 1 064 nm in the porous silicon/PMMA-DR1 waveguide. The diffraction efficiency of the first order diffracted light is measured to be about 0.2% of the total output.     

Temperature Effects on Photoluminescence Properties of Porous Silicon

The temperature effects on the photoluminescence（PL） properties of porous silicon（PS） have been observed in the early stage. However, the obtained results are different. Through repeated experiments, some different and useful information are got, which benefits us in that PL properties of porous silicon can be fully made use of. Firstly, samples with porosity of 76% and 49% were chosen to study the exciting temperature effects on the PL spectrum. For the samples with low porosity, the decreasing temperature causes the peak wavelength to be red-shifting and that of the samples with high porosity to present the blue-shifting trend. The light intensity of both reaches the maximum at - 10℃. These experimental results can be well explained with the synthesized center PL model based on the quantum confinement model, other than the PL efficiency function σ（λ）. Thereafter, PL properties of PS samples fabricated separately under the temperature of -10 ℃, 0 ℃ , 10 ℃, 20 ℃ and 30 ℃ were studied. The results indicate that with the decrease of the etching temperature, the PL intensity increases from 406.7 to 716.6 and the peak wavelength blue-shifts from 698.9 nm to 671.8 nm. The WHFM of the PL spectrum dramatically narrows. At the same time, the images observed by AFM show that with the decreasing temperature, the holes are becoming deeper and the porosity is higher, which suggests that the decreasing temperature accelerates the etching rate.     

多孔硅/聚合物复合膜光学各向异性的研究

首次用二维圆柱孔模型研究了多孔硅/聚合物复合膜的光学各向异性,求出了光学各向异性参数。实验上制备出了多孔硅/PMMA复合膜平面波导,采用棱镜耦合m线方法测量了复合膜的折射率。理论分析与实验结果基本相符。研究结果表明,多孔硅膜呈现出正单轴晶体的特征,由TE和TM模射所确定的折射率分别对应寻常光折射率和非寻常光折射率。多孔硅/PMMA复合膜光学各向异性随聚合物嵌入率的增加而减小。光学各向异性也随孔隙率的不同而变化,当初始孔隙率为73%时,光学各向异性参数β取最大值。     

Low-power thermooptical tuning of SOI resonator switch

A wavelength selective optical switch is developed based on a high-Q racetrack resonator making use of the large thermooptic coefficient of silicon. The racetrack resonator was fabricated using a silicon-on-insulator (SOI) single-mode rib waveguide. The resonator shows a high Q factor of 38 000 with spectral sidelobes of 11 dB down and can be thermooptically scanned over its full free-spectral range applying only 57 mW of electrical power. A low power of 17 mW is enough to tune the device from resonance to off-resonance state. The device functions as a wavelength selective optical switch with a 3-dB cutoff frequency of 210 kHz.     

多孔硅异质结电致发光器件发光特性研究

多孔硅电致发光性质的研究对于实现硅基光电集成具有重要的应用价值。采用蒸镀-阳极氧化法制备了多孔硅异质结(ITO/PS/p-Si/Al)电致发光器件,在7.5V较低电压下实现了数小时连续电致发光,并给出了该器件的发光和电学性能的测量结果。结果表明,要制备较好发光性能和伏安特性的多孔硅电致发光器件,顶部电极应同时具有较高的透光率和电导率。     

低阻硅衬底上形成的低损耗共平面波导传输线

在厚膜多孔硅 (PS) /氧化多孔硅 (OPS)衬底上 ,结合聚酰亚胺涂层改善表面 ,研制低损耗、高性能射频 (RF) /微波 (MW)共平面波导CPW(CoplanarWaveguide) .通过在N和P型硅上形成不同厚度PS膜 ,并对其上的CPW进行分析比较 ,厚膜PS与石英的共面波导插入损耗非常接近 ,远小于在 2 0 0 0Ω·cm高阻硅上形成的多晶硅 -氧化硅组合衬底 :在 0 33GHz范围 ,插入损耗小于 5dB/ 1.2cm ;33 4 0GHz范围 ,小于 7.5dB/ 1.2cm .     

Design of Wide-Band, Sharp-Rejection Bandpass Filters With Parallel-Coupled Lines

An edge-coupled quarter wavelength resonator and half-wavelength open stubs are used for designing a highly selective wideband bandpass filter (BPF). A homogeneous medium is considered and the even-odd mode approach is used for filter analysis. Next, a microstrip line implementation procedure is described. The filter has sharp rejection, wide stopband, low insertion loss (IL), and fabrication simplicity. A prototype BPF having 69.5% 3-dB fractional bandwidth (FBW) is fabricated. A simple stub modification extends the upper 20-dB stopband to five times that of the filter upper cutoff frequency. Passband IL is within 1.6dB     

Vapor Sensing Theoretical Study on Optical Microcavities

When the organic vapors absorbed to the surface of porous silicon（PS）, capillary condensation takes place due to the porous structure of the PS layer, accordingly resulting in the effective refractive index changing. For PS multi-layer microcavities, the different resonant peaks shift in the reflectivity spectrum of porous silicon microcavities（PSMs）. The optical sensing model is set up by applying Bruggeman effective medium approximation theory, capillary condensation process and transfer matrix theoretically analytical method of one-dimensional photonic crystals. At the same time, comprehensively researched on are the sensing characteristics of PSMs which are exposed to give concentration organic vapors. At last, made is the theoretical simulation for sensing model of the PSMs in case of saturation by using computer numerical calculation, and found is the linearity relation between the refractive index of organic solvent and the peak- shift. At the same time deduced is the peak-shift as a function of the concentration of ethanol vapors.     

氧化多孔硅周期性波导光栅耦合器的实验研究

报道了用两束相干激光在HF溶液中的多孔Si(PS)表面上干涉形成光强周期分布,通过光溶解得到了孔隙率周期变化的结构,从而制备出氧化PS周期性波导光栅。实现了辐射模与波导中传输模之间的耦合,并由外部入射光波或衍射光的方向确定了波导层的有效折射率。     

多孔硅吸收光谱和反射光谱

测定了多孔硅的吸收光谱和反射光谱，结果发现其吸收边对应于可见光区域。同单昌硅要比，其吸收边发生了蓝移，并且吸收强烈。由多孔硅反射谱曲一，利用Ｋ－Ｋ关系对其光学常数进行了简单的计算和分析。     

Temperature: a critical parameter affecting the optical properties of porous silicon

The optical properties of porous silicon (PS) samples fabricated by pulse etching in a temperature rangefrom -40 to 50 ℃ have been investigated using reflectance spectroscopy, photoluminescence spectroscopy, and scanning electron microscopy (SEM). The dependence of the optical parameters, such as the refractive index n and the optical thickness (nd) of PS samples, on the etching temperature has been analyzed in detail. As the etching temperature decreases, n decreases, indicating a higher porosity, and the physical thickness of PS samples also decreases. Meanwhile, the reflectance spectra exhibit a more intense interference band and the interfaces are smoother.In addition, the intensity of the PL emission spectra is dramatically increased.     

温度：影响多孔硅光学特性的一个关键参数

The optical properties of porous silicon（PS） samples fabricated by pulse etching in a temperature range from-40 to 50-C have been investigated using reflectance spectroscopy,photoluminescence spectroscopy,and scanning electron microscopy（SEM）.The dependence of the optical parameters,such as the refractive index n and the optical thickness（nd） of PS samples,on the etching temperature has been analyzed in detail.As the etching temperature decreases,n decreases,indicating a higher porosity,and the physical thickness of PS samples also decreases.Meanwhile,the reflectance spectra exhibit a more intense interference band and the interfaces are smoother.In addition,the intensity of the PL emission spectra is dramatically increased.     

基于回音壁模式的球形光学微腔实验研究

采用聚苯乙烯材料制作出不同直径(50～250μm)的球形光学微腔并实现了微腔与锥形光纤的耦合,测量了球形光学微腔在1570～1576nm波长范围内的吸收光谱,实验结果表明球形光学微腔在这一波长范围内可发生基于回音壁模式(WGM)的光学谐振,且WGM吸收峰的相邻波长间隔随着聚苯乙烯微球直径的增大而减小。通过吸收光谱计算了聚苯乙烯微球在其本征频率下的品质因子,结果表明微球品质因子数量级均在104以上。     

钝化多孔硅的光致发光

选用含有胺基的正丁胺 (CH3CH2 CH2 CH2 - NH2 )作碳源 ,采用射频辉光放电法制备碳膜对多孔硅进行碳膜钝化 ,其光致发光谱和存放实验表明 :正丁胺对多孔硅进行钝化是一种十分有效的多孔硅后处理途径 .研究了钝化多孔硅的光致发光谱随钝化温度和钝化时间的变化关系 ,其结果显示 :通过调节钝化条件可实现钝化多孔硅最大的发光效率和所需要的发光颜色     

Optical study of porous silicon buried waveguides fabricated from p-type silicon

The realisation of optical buried waveguides fabricated from porous silicon layers is presented. The refractive index of porous silicon layer varies according to its porosity and its oxidisation process conditions. So either step or graded index waveguides are achieved. These waveguides are formed by a localised anodisation of heavily doped p-type silicon wafers. Measurements at a wavelength of 1.3 μm yield waveguide losses below 4 dB/cm. The waveguides are also characterised by the near-field-guided mode profile at 1.3 μm. This study deals with the modulation of the waveguiding-layer refractive index and the losses on waveguides fabricated from p⁺.     

Transmission of a microcavity structure in a two-dimensional photonic crystal based on macroporous silicon

Photonic crystals consist of regularly arranged dielectric scatterers of dimensions on a wavelength scale, exhibiting band gaps for photons, analogous to the case of electrons in semiconductors. Using electrochemical pore formation in n-type silicon, we fabricated photonic crystals consisting of air cylinders in silicon. The starting positions of the pores were photolithographically pre-defined to form a hexagonal lattice of a=1.58 μm. The photonic crystal was microstructured to make the photonic lattice accessible for optical characterization. Samples with different filling factors were fabricated to verify the gap map of electric and magnetic modes using Fourier-transform infrared (IR) spectroscopy. The complete band gap could be tuned from 3.3 to 4.3 μm wavelength. We were able to embed defects such as waveguide structures or microcavities by omitting certain pores. We carried out transmission measurements using a tunable mid-IR optical parametric oscillator. The resonance is compared with theoretical expectations.     

多孔硅发光器件的设计与试验

设计了多孔硅电致发光器件，讨论了工艺条件对器件Ｉ—Ｖ特性影响。试验中已观察到微弱的电致发光。认为利用多孔硅制备可见光发光器件是可行的。