多孔硅的制备和发光特性

本文叙述了多孔硅的制备、多孔形态层的形成机理,以及多孔硅的光致发光现象和理论解释,并且讨论了目前存在的一些问题。     

多孔硅薄膜的纵向均匀性及其光学特性研究

多孔硅样品使用脉冲电化学腐蚀法经过不同的腐蚀时间制备完成,使用反射光谱、光致发光光谱和SEM对多孔硅薄膜的纵向均匀性以及其光学特性进行了研究,还详细研究了随腐蚀深度变化的折射率和光学厚度(n*d)等光学参数。实验表明：随着腐蚀深度的增加,多孔硅薄膜的平均折射率n降低,即多孔度变大;多孔硅薄膜的光学厚度的形成速度减小;同时,反射光谱表现更弱的干涉性,表明薄膜的均匀性和界面的平整性变差;另外,光致发光谱的强度微弱变强。     

通过脉冲腐蚀形成的多孔硅薄膜的径向微结构和光学特性研究

使用反射光谱、光致发光光谱和SEM研究了通过脉冲腐蚀形成的多孔硅薄膜的径向折射率、光学和物理厚度。详细分析了沿径向方向多孔硅薄膜的径向折射率(n)和光学厚度(nd)与腐蚀中心之间的关系。实验结果表明：随着远离腐蚀中心,SEM图像表明：多孔硅样品的物理厚度缓慢变小,在腐蚀边缘,在径向58μm距离里,薄膜的物理厚度从2.48μm减少到1.72μm;此外,径向折射率n增加,即多孔度变小,同时,反射光谱强度显示出干涉振荡减弱,这意味着多孔硅薄膜的均匀性和界面的平整度变坏。光致发光谱的包络线显示蓝移的趋势,显示纳米微粒的尺寸减少。多孔硅微腔被制备用来研究多孔硅膜的径向光学特性,结果证实：在腐蚀中心,多孔硅膜的均匀性比边缘好。     

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.     

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.     

硫化锌/多孔硅体系和氧化锌/多孔硅体系的光学和电学特性比较

用脉冲激光沉积法在相同孔隙率的多孔硅(Porous Silicon, PS)衬底上生长了ZnS薄膜和ZnO薄膜,在室温下对ZnS/PS和ZnO/PS的光学和电学性质进行了比较.结果发现,ZnS/PS和ZnO/PS在可见光区450～700 nm都有一个较宽的光致发光谱带,呈现较强的白光发射,但ZnS/PS体系的白光发射性能要优于ZnO/PS体系的发光性能.从二者的I-V特性曲线来看,ZnS/PS异质结呈现出与普通二极管相似的整流特性,而ZnO/PS异质结的整流特性与普通二极管不同,其反向电流不饱和.     

铁钝化多孔硅的水热制备法及其光致发光特性

利用水热技术原位制备出铁钝化多孔硅样品,并对其发光特性进行了测试。样品具有较强的光致发光强度,而且在室温空气存放过程中其发光强度不发生衰减,发光峰位不发生蓝移。上述发光特性归因于样品表面形成的良好铁钝化。     

石墨烯对多孔硅光学性能的影响北大核心

采用电化学腐蚀法,通过改变腐蚀电流密度制备出不同孔径的多孔硅衬底。通过荧光分光光度计对多孔硅进行光致发光性能测试,测试结果发现腐蚀电流密度会对其光致发光性能产生影响,当腐蚀电流密度为30 mA/cm^2时,制备出的多孔硅光致发光性能较好。通过湿法转移法将化学气相沉积(CVD)法制备出的石墨烯转移到多孔硅表面,利用喇曼光谱对石墨烯进行质量及层数检测。通过荧光分光光度计及傅里叶变换红外光谱仪(FTIR)对复合材料进行表征。结果表明石墨烯可以改变多孔硅表面态,使多孔硅的光致发光性能得到极大的提高。研究成果为多孔硅应用到光学传感器中提供了新的研究方向。     

在多孔硅衬底上制备的ZnS薄膜及其光学性能

用脉冲激光沉积（PLD）方法在多孔硅（Ps）衬底上沉积了ZnS薄膜。用x射线衍射仪（XRD）、扫描电子显微镜（SEM）、荧光分光光度计分别研究了ZnS薄膜的晶体结构、表面形貌及光学性能。结果表明,ZnS薄膜呈立方相晶体结构,沿β-ZnS（111）晶向择优取向生长;经过300℃真空退火30min后,ZnS薄膜的XRD衍射峰强度增大,表面变得粗糙,在可见光区的平均透射率达到80％以上,适合作太阳能电池过渡层、红外增透膜、红外窗口和头罩等。在退火后的ZnS／PS复合膜体系的光致发光谱（PL）中,除了高能端ZnS的蓝光发射和低能端Ps的红光发射外,在光谱中间550nm附近出现了一个新的绿光发射,这归因于ZnS薄膜退火过程中形成的缺陷能级而产生的缺陷中心发光。根据三基色叠加的原理将ZnS的蓝、绿光与Ps的红光叠加在一起后,ZnS／PS复合膜体系呈现出了较强的白光发射,这为固态白光发射器件的实现开辟了一条新的捷径。     

钝化多孔硅的光致发光

选用含有胺基的正丁胺(CH3CH2CH2CH2-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.     

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.     

Radial microstructure and optical properties of a porous silicon layer by pulse anodic etching

This paper investigates the radial refractive index and optical and physical thicknesses of porous silicon (PS) layers prepared by pulse etching by means of reflectance spectroscopy,photoluminescence spectroscopy and scanning electron microscopy(SEM).The relationship between the radial refractive index and optical thickness of the PS sample and the position away from the etched centre along the radial direction has been analyzed in detail. With the position farther away from the etched centre,the SEM image shows that the physical thickness of the PS sample decreases slowly,whereas intensely decreases from 2.48 to 1.72μm near the edge at a distance of 58μm.Moreover,the radial refractive index increases,indicating that the porosity becomes smaller.Meanwhile,the reflectance spectra exhibit the less intense interference oscillations,which mean that the uniformity and interface smoothness of the PS layers become worse,and the envelope curves of photoluminescence spectra exhibit a trend of blue-shift,indicating a reduction in nanocrystal dimensions.The PS micro-cavity is prepared to study the radial optical properties of the PS layer,and the results verify that the uniformity and smoothness of the PS layer in the centre are better than those at the edge.     

Downward uniformity and optical properties of porous silicon layers

Porous silicon (PS) samples were fabricated by pulse current etching using different times. The downward uniformity and optical properties of the PS layers have been investigated using reflectance spectroscopy, photoluminescence spectroscopy, and scanning electron microscopy (SEM). The relationship between the refractive index and the optical thickness of PS samples and the etching depth has been analyzed in detail. As the etching depth increases, the average refractive index decreases, indicating that the porosity becomes higher, and the formation rate of the optical thickness decreases. Meanwhile, the reflectance spectra exhibit less intense interference oscillations,which mean the uniformity and interface smoothness of the PS layers become worse. In addition, the intensity of PL emission spectra is slightly increased.     

Ar^＋注入多孔硅与Ar^＋注入硅多孔结构的光致发光研究

研究了中等能量(30 key)Ar+注入多孔硅和中等能量(30 key)Ar+先注入单晶硅后再进行电化学腐蚀成的多孔结构的光致发光特性.研究结果表明:中等能量(30 key)Ar+注入多孔硅后,多孔硅原有的发光峰消失,主要是Ar+对多孔硅表面氧的剥离作用.使得与氧相关发光的结构消失,多孔硅不再发光;中等能量(30 kev)Ar+先注入单晶硅后冉电化学腐蚀成的多孔结构中,通常多孔硅原有的580 nIn附近发光峰强度随注入Ar+剂量的增加而增强,并有红移;同时在谱峰处于470 nm附近的微弱发光峰不因注入Ar+而明显变化.     

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。     

一种多孔硅生物免疫传感器的研究

对多孔硅样品进行热氧化和硅烷化处理,通过共价结合的方法将HYSA生物抗体固定到多孔硅的孔洞中;测量了加入BSA发生抗原抗体反应前后的荧光光谱和反射谱.实验结果表明加入生物分子后多孔硅发光峰消失,抗原抗体反应后发光强度增强,反射谱红移.该项研究为开发免标记的多孔硅光学生物免疫传感器奠定了基础.     

Simulation and implementation of a porous silicon reflector for epitaxial silicon solar cells

One of the main challenges in the ongoing development of thin film crystalline silicon solar cells on a supporting silicon substrate is the implementation of a long‐wavelength reflector at the interface between the epitaxial layer and the substrate. IMEC has developed such a reflector based on electrochemical anodization of silicon to create a multi‐layer porous silicon stack with alternating high and low porosity layers. This innovation results in a 1–2% absolute increase in efficiency for screenprinted epitaxial cells with a record of 13·8%. To reach a better understanding of the reflector and to aid in its continued optimization, several extensive optical simulations have been performed using an in‐house‐developed optical software programme. This software is written as a Microsoft Excel workbook to make use of its user‐friendliness and modular structure. It can handle up to 15 individual dielectric layers and is used to determine the influence of the number and the sequence of the layers on the internal reflection. A sensitivity analysis is also presented. A study of the angle at which the light strikes the reflector shows separate regions in the physical working of the reflector which include a region where the Bragg effect is dominant as well as a region where total internal reflection plays the largest role. The existence of these regions is proved using reflection measurements. Based on these findings, an estimate is made for the achievable current gain with an ideal reflector and the potential of epitaxial silicon solar cells is determined. Copyright © 2008 John Wiley & Sons, Ltd.     

一维多孔硅光子晶体的三阶非线性光学性质

在工艺参数实验和理论设计分析的基础上,制备 了包括多孔硅Bragg反射镜、多孔硅微腔和稳定 性很好的多孔硅三元结构在内的多孔硅一维光子晶体,对3种多孔硅光子晶体的结构进行了 表征,不同孔 隙度的多孔硅呈现出周期性的排列。采用单光束反射Z扫描方法 分别对3种结构的多孔硅在1064nm波长处的 非线性折射率进行了测量。实验结果表明,多孔硅三元结构光子晶体的三阶非线性折射率比 多孔硅Bragg 反射镜和多孔硅微腔高1个数量级,这将为多孔硅一维光子晶体用于先进光电器件的设计提 供了重要参考。