表面修饰N型多孔硅的光致荧光特性

【作者】 贺月娇；

【导师】 李怀祥；

【作者基本信息】 山东师范大学 ， 微电子学与固体电子学， 2001， 硕士

【摘要】 多孔硅（PS）是近年来发展起来的一种新型硅基材料，具有与单晶硅材料大不相同的特性，例如，多孔硅可在近红外和可见，甚至近紫外区辐射强烈的荧光，使得它可用来制造发光器件，并可望在解决光电子集成电子学的关键问题，为制造带有光源的大规模集成电路等方面开辟新的途径。本文在用三种电阻率的n型硅片为基底制成室温紫外灯下发强橙光的多孔硅基础上，对多孔硅进行三种表面修饰，实现了多孔硅的红、绿、蓝光发射，并对其发光机理进行了探讨。 本体硅为间接禁带半导体，且禁带宽度较窄，室温下很难发光。多孔硅改变了体硅的能带结构，使禁带展宽，并由间接带隙向直接带隙转变，实现了室温发光。在比较了制备多孔硅的几种常用方法的基础上，概括多孔硅的光致荧光（PL）和电致荧光（EL）特性，对目前比较流行的几种发光模型给出了定性的论述，展望了多孔硅的应用前景。多孔硅表面存在大量的悬挂键，容易引起发光效率的降低，行之有效的克服方法是进行表面修饰。常见的表面修饰方法包括对多孔硅表面进行氢钝化、氧钝化、氮钝化、金属钝化等，这些修饰方法各有其特点。 在实验设计方面，首先在三种电阻率差别较大（分别为n^--Si：80～100Ω·cm；n-Si：3～5Ω·cm；n⁺-Si：0.003Ω·cm）的n型单晶硅片上阳极氧化出在紫外激发下发强橙光或红光的多孔硅，然后对多孔硅样品进行三种不同的表面修饰：（1）涂覆四氯化锡的饱和乙醇溶液；（2）涂覆1.0mol/l四氯化锡，0.03mol/l三氯化锑的乙醇溶液；（3）将PS浸入胺液的混合液：（C₂H₅）₃N：C₂H₄（NH₂）₂=3:2中，并结合进行快速热氧化。比较多孔硅光致荧光性能与未修饰时的不同，并对其表面形貌和化学成分进行表征。 摘要 系统研究了阳极氧化条件对n型多孔硅光致荧光特性的影响。考察了电化学刻蚀电流密度。刻蚀时间、刻蚀液配比及衬底电阻率对PL发光强度、峰值波长等性质的影响。在此基础上优化出制备多孔硅的具体参数。 对不掺Sb与掺Sb的SnCI。修饰后的多孔硅进行了光致荧光特性研究。发现这两种差不多的修饰却出现两种不同峰移现象；前者PL与未修饰多孔硅相比发生蓝移，峰值波长在540－560urn（绿光），而后者发生红移，峰值波长在650－690urn（红光）。此现象不能仅用量子限制（QC）效应解释。通过AFM、SEM及FTIR、XPS对这两种多孔硅样品进行表面形貌和化学成分分析，采用发光中心（LC）＋量子限制效应的复合模型对上述修饰多孔硅的PL峰移现象进行了理论说明。电于空穴对在纳米硅粒或硅线中被激发，隧穿到包围纳米硅的氧化层中通过发光中心实现辐射复合。不掺Sb的SZOZ与ax层中的发光中心发射的光子能量为2．ZCV，掺Sb 的SflOZ与 引x层中的发光中心发射的光子能量为1．ge V o 对多孔硅进行“胺液浸泡＋干氧氧化”处理后，多孔硅样品的nr峰值波长缩短为 415－440 urn（蓝光），且在室温空气中存放近一年后，发光强度略有增强。FTIR谱表明，处理后的多孔硅主要成分为硅与氧，胺液没有在样品中留下残迹。由AFM、SEM等形貌图可以看出，处理后的样品孔隙率很高，表面呈蜂窝状。从发光强度取对数与退火温度倒数的Arrhenius曲线上，发现在低温区（200－400aC）和高温区（600－900aC）分别对应着两种激活能：0．35eV和 0．64eV，表明蓝光发射存在两种发光机制。更多还原

【Abstract】 Porous silicon (PS) is a new type silicon-based material developed in recent years,which has different properties compared with the crystalline materials. Porous silicon canluminescence efficiently across the whole range from the near infrared ,through thevisible region, to the near UV region. This characteristic makes it possible to fabricatelight-emitting devices and solve the key problem of the optoelectronic integratedcircuit(QEIC), opening up the bright future for the VLIC. In this thesisphotoluminescence(PL) properties of n-type porous silicon modified in three differentways have been studied. The silicon wafers with different resistivities were anodizedphotoelectrochemically to form PS. After modification, red, green and blue PL can beobserved under the UV light from the original orange-emitting as-prepared PS samples.The mechanism of the luminescence has been discussed.Bulk silicon, with indirect band gap of 1.12eV doesn’t emit light at roomtemperature. With a broaden and likely direct band gap, porous silicon has a differentband structure to that of the bulk silicon. Thus the porous silicon can emit at roomtemperature. Several methods commonly used in preparing porous silicon are presented.Photoluminescence and electroluminesce(EL) properties of porous silicon aresummarized. Qualitative description is given for the prevalent mechanisms proposed toexplain the bright PL and EL. Dangling bonds exist at the surface of porous silicon,which leads to the drop of the light-emitting efficiency. To apply porous silicon intopractice, surface modification is necessary. Various surface passivations of PS, such as byhydrogen, oxygen, nitrogen and noble metals, have been compared.The PSs were formed by photoelectrochemical means. Anodization was carried outon n-type silicon substrates with three different resistivities(n - ?Si: 80?00&cm; 鵱 ?Si: 3?flcm; n~ Si: O.OO3~cm). The orange-emitting as-anodized porous silicon wasmodified by following methods: (1 )coating the PS with saturated ethanol solution of tintetrachloride; (2) coating the PS with ethanol solution of I .Omol/l tin tetrachloride dopedwith O.O3molIl antimony chloride; (3) immersing the wafers with PS layers into a mixtureof amine: (C2H5)3N: C2H4(NH2)2 3:2 for 20 mm , then carrying on rapid thermaloxidation(RTO) through a quartz tube. PL properties of modified and unmodified PS are-4-Abstractquite different. The morphology and the surface species of the PS samples wereexamined.The oxidizing parameters of the anodization in the following experiments werepreferred on the basis of measuring the dependence of PL properties (peak position, andmax intensity, etc.) on anodization conditions, such as the anodizing current density, thetime of the anodization, the concentration of the solution (mainly of HF), and on thedoping level of the substrate.As for the PL properties of porous silicon modified by SnC14 with or withoutSb-doping, there are two kinds of shifts compared with the unmodified samples.Blue-shift of the PL peak position with the max wavelength 540-560 nm (green-emitting)for the latter(without Sb-dopirfg) and red-shift of the PL peak position with the maxwavelength 650-690 nm(red-emitting) for the former( with Sb-doped) are observed. Thequantum confinement effect(QC) model is obviously not enough to explain the aboveexperimental results. The complex model of luminescence centers and quantumconfinement has been proposed to interpret the origin of the green and red-emitting of thePS after modification. The deduction is supported by analyzing the morphology and thesurface species of the modified samples through AFM, SEM, and FTIR, XPS.Electron-hole pairs are created by photo-excitation in the nanoscale silicon units, and thenrecombined radiatively in t更多还原