【作者】 林琳涵；

【导师】 冯嘉猷；

【作者基本信息】 清华大学 ， 材料科学与工程， 2013， 博士

【摘要】 半导体硅是当前微电子技术领域中最为重要的材料之一，然而硅的间接带隙能带性质限制了其在光电子领域的进一步推广。如果可以实现硅的能带结构转变，不仅可以为全硅基光通讯技术的实现提供材料基础，还可以促进太阳能电池和固态发光器的应用发展，同时也是能带工程的一个重要突破。硅纳米材料是硅能带工程中一个重要的研究方向。本文采用第一性原理研究了氧钝化网络硅的电子能带结构，结果表明，100X和100D的氧钝化网络硅模型，随着孔隙率的增加，能带结构发生从间接带隙往直接带隙的转变，并且Si－O－Si键对能带结构表现出良好的调节作用。利用－H、－O、－N三种不同官能团研究表面钝化对能带结构的改性作用，发现利用电负性强的氧钝化不仅可以促使网络硅的能带结构往直接带隙转变，而且有利于维持直接带隙的带边单一性，提高电子辐射跃迁效率从而改善发光性能，表面钝化对能带改性的作用机制源自态分布效应。同时，本文构建了一种新的硅二维纳米结构——超薄硅薄膜，对于薄膜表面为(100)和(110)的硅薄膜，当其厚度分别达到1.05nm和1.14nm以下时，其能带结构实现从间接带隙到直接带隙的转变。利用部分态密度对其电子态分布进行分析可知，其能带转变是量子效应与表面官能团相互竞争的结果。为了验证网络硅的理论模型，本文利用金属催化化学腐蚀的方法在高掺单晶硅片上制备多孔硅纳米线阵列，多孔纳米线同时包含一个在氧化层的界面态中辐射复合产生的红光发光峰和一个氢钝化多孔结构中量子效应引起的近红外发光峰，并可通过改变表面钝化条件对发光性能进行调控。后续的硒化处理可将多孔纳米线的发光强度提高约30倍，并且极大提高了其发光稳定性，利用瞬态荧光光谱测得硒化多孔硅纳米线在570nm处包含寿命分别为0.49ns和2.68ns的发光峰，分别由Si－Se和Si－Se－O钝化的纳米多孔结构所贡献，该纳秒量级的荧光寿命表明硒化多孔硅纳米线中的发光现象是由表面Se钝化诱导的直接辐射复合跃迁。硅纳米线的尺寸调控决定了其能否在光电子领域获得应用。为了制备出小尺寸的硅纳米线阵列，本文采用模板辅助的金属催化腐蚀和干法氧化的方法，实现对硅纳米线直径的精确控制，并利用氧化自饱和效应，成功制备内核直径在10nm以下的core-shell结构纳米线阵列，其结构参数有望得到进一步优化。更多还原

【Abstract】 Silicon is one of the most important materials in the area of microelectronic.However, the indirect band-gap structure restricts its further application inoptoelectronics. The transition from indirect to direct band-gap could open a way for theachievement of all-silicon optical communication, greatly facilitate the development ofsolar cell and solid-state luminescence devices, and also be available in the band-gapengineering in solid state physics.Silicon nanostructure is one of the possible candidates to realize the band-gaptransition. Systematical investigation on the band-gap structure of oxygen-passivatedsilicon nanonets (SiNNs) with different parameters were carried out. It was foundthat high porosity was favorable for the direct band-gap and the Si－O－Si bondcould effectively modify the band edge characteristic. Different funcionalgroups, such as－H,－O and－NH, were employed to terminate the danglingbonds of the SiNNs and silicon nanowires (SiNWs). It was found thatpassivation with－O functional groups could not only lead to the indirect todirect band-gap transition, but also enhance the transition efficiency andimprove the luminescene properites by increasing the electron states on the bandedge. State distribution effect were proposed to explain this phenomenon. Thestudy on the two dimensional silicon quantum films indicated that when the thicknessreached1.05nm and1.14nm for (100) and (110) quantum films, respectively, thedirect band-gap was also securable, which was attributed to the competition of quantumconfinement and surface electron states.In order to validate the models of SiNNs, metal-assisted chemical etching wasemployed to obtain the nanoscale and controllable porous structure on the nanowiressynthesized on the highly doped silicon wafer. A red luminescence band and anear-infrared one were detected in the photoluminescene (PL) measurement, whichwere attributed to interface recombination in the oxide layer and localized excitation inthe H-terminated porous structure, respectively. Selenization treatment was carried outon the porous SiNWs. An enhancement of30times of the luminescence intensity andwonderful stability were obtained. Time-resolved luminescence spetra proved that therecombination rate was three magnitudes faster after Seleniazation treatment. The lifetime of0.49ns and2.68ns were attributed to the recombination in the Si porousstructure passivated with Si－Se and Si－Se－O bonds, respectively. The fastrecombination rates indicated that surface modification induced by selenizationtreatment could lead to the direct radiative recombination in this Se-treated Siporous structure.The diameter of the SiNWs is crucial for its future application in optoelectronics.Ag-assisted chemical etching with polystyrene (PS) sphere as template was employed toprepare the SiNW arrays and the diameter could be controlled via high-temperatureoxidiation and etching. The core-shell nanowire arrays with silicon core diameter lessthan10nm was successfully synthesized due to the self-terminating effect. It isexpected that the structure parameter could be optimized in the future.更多还原