【作者】 胡振纲；

【导师】 李新建；

【作者基本信息】 郑州大学 ， 凝聚态物理， 2014， 博士

【摘要】 硅纳米孔柱阵列（Silicon nanoporous pillar array，Si-NPA）是一种典型的多孔材料和硅纳米晶（Silicon nanocrystallites， nc-Si）/氧化硅（SiOx）纳米复合体系，研究其在光学过程中的电子跃迁特性有助于进一步了解Si-NPA各种物理特性的内在机制，为未来设计和制备基于Si-NPA的不同功能纳米异质结器件提供基础性的理论支持。本文综合利用了表面光电压（Surface photovoltage, SPV）谱、光致发光（Photoluminescence, PL）谱等对水热法和染色腐蚀法制备的Si-NPA、经过不同温度热处理的Si-NPA和基于Si-NPA制备的聚乙烯咔唑（PVK）/Si-NPA有机-无机复合结构进行了研究，得到了一下主要结论：一、Si-NPA多孔层中nc-Si/SiOx纳米结构的电子跃迁特性对比单晶硅和Si-NPA的SPV谱发现，Si-NPA多孔层中nc-Si/SiOx纳米结构在~580nm-~300nm的波长范围内具有明显的SPV响应。在外加不同电场时，nc-Si/SiOx纳米结构的SPV响应完全不同于单晶硅层SPV响应的变化规律，说明nc-Si/SiOx纳米结构的SPV被nc-Si/无定形SiOx界面上某种界面局域电子态所主导。对Si-NPA在空气中进行退火氧化，随着退火温度从100℃升至500℃时，位于~580nm到~300nm之间来自多孔层的SPV响应会逐渐减弱直至几乎完全消失；同时，位于红光区的单PL带在200℃时分裂为两个PL带，500℃时大幅减弱直至完全消失；位于红光-近红外区的PL带则逐渐增强。与此同时，在紫光-蓝光区内出现一新的PL带形成并逐渐增强。Si-NPA经过两年空气中自然氧化后，来自于单晶硅层的SPV完全消失，仅表现出多孔层nc-Si/SiOx纳米结构的光吸收特征。分析表明，Si-NPA样品中多孔层nc-Si/SiOx纳米结构的SPV和红光PL都是来自于nc-Si与无定形SiOx结构的界面上Si-O结构相关的界面局域电子态所主导的电子跃迁，而位于红光-近红外区域的PL来源于与Si=O结构相关的局域电子态所诱导的复合发光，紫光-蓝光PL来自于nc-Si表面上所形成的O缺陷所诱导的复合发光。二、Si-NPA电子跃迁特性在不同制备过程中的变化水热法制备的不同腐蚀时间的SEM照片表明只有当腐蚀时间超过25分钟以上时在多孔层中才能形成规则的纳米多孔硅阵列结构。比较各个样品的SPV谱，发现当腐蚀时间从10分钟增加到45分钟的过程中各个样品的光吸收特征发生了很大的变化，这主要归因于nc-Si粒径尺寸分布在不同腐蚀时间样品中的不同。在~5800nm到~300nm的波长区间内出现的SPV响应带的强度会随着水热腐蚀时间从10分钟变化到45分钟的过程逐步减弱，而且位于~550nm-~800nm波长区间内的PL带的强度也会随着减弱，这些结果都说明在水热腐蚀时间增加的过程中多孔层nc-Si/无定形SiOx结构的界面上的氧化程度在逐步下降，并且导致了界面上与Si-O结构相关的界面局域电子态的数量也在逐步下降。染色法制备不同腐蚀时间的Si-NPA样品的SEM照片表明只有当腐蚀反应在30小时以上时才有规则纳米多孔硅柱结构形成，但是其硅柱的尺寸要远大于水热制备Si-NPA样品中的多孔硅柱。对比所有染色腐蚀Si-NPA样品及在空气中500℃退火氧化后样品的SPV谱，可以发现它们的多孔层nc-Si/SiOx纳米结构的光吸收特性远不同于水热腐蚀Si-NPA样品，说明染色腐蚀Si-NPA样品的多孔层中有更多大粒径的nc-Si生成；而30小时、40小时和50小时染色腐蚀Si-NPA样品的SPV谱在~500nm到~300nm的波长范围内都有一个非常强的SPV响应带，而且它们的PL谱中都有很强的可见光PL，但是这些样品的SPV响应强度和PL强度对于不同腐蚀时间没有表现出规律性，最终表明，利用染色腐蚀法无法实现像水热法那样对于Si-NPA样品光学特性某种程度上的可控。三、PVK/Si-NPA复合结构对比PVK/Si-NPA复合结构和Si-NPA样品的SPV谱及PVK薄膜的吸收光谱，可以发现PVK/Si-NPA复合结构的光吸收特性和光发射特性出现了很多新的现象，这些新的现象都可能来源于复合结构中PVK分子与Si-NPA中多孔层nc-Si/SiOx纳米结构之间的相互作用，而且基于复合结构而制备得到的Ag/c-Si/PS/PVK/Ag结构器件的I-V特性则进一步证实了PVK分子与Si-NPA中多孔层nc-Si/SiOx纳米结构之间的相互作用的可能性。更多还原

【Abstract】 Silicon nanoporous pillar array (Si-NPA) is a typical porous silicon material anda special type of the nc-Si/SiOxnanostructures. Study on the electronic transitionmachanisms during the optical processes can afford the detailed principles of thephysical properties of Si-NPA, and can provide the fundamental theorical surpportsfor designing and constructing the Si-NPA based nanocomposite devices with thedifferent physical properties. In this dissertation, the optical and electric properties ofSi-NPA samples (prepared by hydrothermal method and stain method) and thepoly(N-vinylcarbazole)(PVK)/Si-NPA nanocomposite are investigated by usingsurface photovoltage (SPV) spectroscopy, photoluminescence (PL) spectroscopy andcurrent-voltage (I-V) characteristics. The main achieved results in this dissertation arelisted as the followings:1. Electronic transition machanisms of the porous layer in Si-NPABy comparing the SPV spectra of single crystal silicon (sc-Si) with that ofSi-NPA, the silicon nano-crystallites (nc-Si)/SiOxnanostructure in the Si-NPA couldproduce SPV in the wavelength range of580–300nm. And580nm (~2.14eV) wasconsidered as the absorption edge of the nc-Si/SiOxnanostructure. And the SPV forthe sc-Si layer and the nc-Si/SiOxnanostructure show some contrary characters in thedifferent external electric field. Through analysis, some kind of localized states at henc-Si/SiOxnanostructure interface are believed having dominated the SPV for thenc-Si/SiOxnanostructure.After the sample was annealed and oxidized in air, and when the annealingtemperature was increased from100to500°C, both the SPV in the wavelength rangeof580–300nm and the PL emission band around690nm for the nc-Si/SiOxnanostructure were weakened and disappeared at high temperatures. But both thered–infrared PL band in the wavelength range from710nm to higher wavelength andthe violet-blue PL band were enhanced by increasing the annealing temperature. After2years of natural oxidation in air, the SPV features for sc-Si disappeared completely, and the SPV characteristics were clearly observed in the nc-Si/SiOxnanostructures.After analysis, the Si-O structure related localized states at the nc-Si/SiOxinterfacedominated the electronic transitions during the red PL emission and the SPV for thenc-Si/SiOxnanostructure in Si-NPA, the red–infrared PL was due to the Si=Ostructure related electronic transitions, and the violet-blue PL emission could attributeto the oxygen-related defect related recombination of the photoinduced carriers.2. Evolutions of the electronic transition properties of Si-NPA during thedifferent preparing methodsScanning electron microscopy (SEM) images of Si-NPA samples, which areprepared by hydrothermal method with the different etching time, show that theregular nanoporous silicon pillars only can be well formed when the etching time islonger than25min. By comparing SPV spectra of the prepared samples, the changesof the photon absorption features of the nc-Si/SiOxnanostructure in the porous siliconlayer can be found with the etching time increasing, and this result can attribute to theformation of lots of nc-Si with larger diameter. When the etching time increasescontinuously, the SPV for the nc-Si/SiOxnanostructure in the wavelength range from~580nm to~300nm was weakened obviously, and the PL emission band in thewavelength range from~550nm to~800nm was also been weakened. These changesof SPV and PL properties all can attribute to decreasing of the native oxidation degreeat the nc-Si/SiOxinterface when the etching time increases from10min to45min.SEM images of Si-NPA samples which are prepared by stain method with thedifferent etching time show that regular nanoporous silicon pillars only can be wellformed when the etching time is longer than30h, but the pillars are much bigger thanthose in the hydrothermal prepared Si-NPA samples. By comparing SPV spectra ofthe stain etched Si-NPA samples and the annealed stain etched samples to those ofsc-Si and hydrothermal prepared Si-NPA sample, the photon absorption features ofthe nc-Si/SiOxnanostructure in the porous silicon layer also show great differences tothose of the hydrothermal prepared Si-NPA sample. This result can attribute to theformation of a lot of bigger nc-Si in the nc-Si/SiOxnanostructure of stain etchedSi-NPA samples. All of30h,40h and50h stain etched Si-NPA samples show the strong PL emission in the wavelength range from~550nm to~800nm and the strongSPV in the wavelength range from~500nm to~300nm. But the PL and SPV intensitydo not show regular relationship with the stain etching time.3. PVK/Si-NPA compositeBy comparing to the photon absorption and PL emission properties of PVK andSi-NPA, the PVK/Si-NPA composite shows the obvious differences, and thesedifferences may come from the interactions between PVK molecules and nc-Si/SiOxnanostructure in Si-NPA. And I-V characteristic of the Ag/c-Si/PS/PVK/Ag devicewhich is based on the PVK/Si-NPA composite also shows the possibility of theinteractions between PVK molecules and nc-Si/SiOxnanostructure in Si-NPA.更多还原