【作者】 徐伟；

【导师】 徐骏；

【作者基本信息】 南京大学 ， 微电子学与固体电子学， 2012， 硕士

【摘要】 硅基光子学和硅基单片光电集成是当前的研究热点和前沿课题之一,其中如何实现基于硅基材料的高效光源问题一直是一个亟待解决的极具挑战性的难题。迄今为止,人们已发展了多种技术途径来克服体硅材料本身的局限,在对各类硅基发光材料的结构、性质进行深入研究的基础上希望能获得高效的硅基发光材料和器件。其中,纳米硅量子点材料作为了一个非常有潜力的硅基发光材料,一直吸引着国内外众多研究小组的关注。本论文在我们小组以往工作的基础上,进一步发展限制性晶化技术,对利用等离子体增强化学气相沉积(PECVD)系统生长制备的非晶硅/二氧化硅(a-Si/SiO2),非晶硅/氮化硅(a-Si/SiNx)三明治结构样品进行KrF准分子脉冲激光晶化处理以获得高密度的纳米硅量子点/二氧化硅(氮化硅)低维发光材料,特别是获得小尺寸(<4rnm)纳米硅量子点材料,着重研究了基于纳米硅量子点的电致发光特性。同时,还利用激光晶化技术,通过晶化沉积在石英衬底上的掺杂非晶硅薄膜,来制备出具有较高导电性的掺杂纳米晶/微晶硅薄膜。初步研究了不同的掺杂比例、薄膜厚度以及激光能量对非晶硅薄膜电学和光学性质的影响。本论文的研究工作的主要内容和结果如下：1.利用限制性晶化技术对沉积在ITO玻璃衬底上的a-Si:H/SiO2多层膜进行激光晶化处理。通过Raman和TEM对薄膜结构进行了表征,证明了经过激光晶化后获得了纳米硅量子点(Si QDs)/SiO2多层膜样品,样品的周期性结构在晶化后仍保持完好。通过改变a-Si:H层的厚度我们最小获得了平均尺寸为1.8nm的纳米硅量子点。在此基础上,构建了电致发光原型器件,在施加外加偏压后,可以观测到电致发光信号。电致发光峰的强度随着偏压的增加而增强。比较了基于两种尺寸的纳米硅量子点电致发光特性,发现小尺寸的纳米硅量子点的电致发光具有较高外量子效率(10-4)。同时发现发光峰可以分为两个子峰,一个位于660nm,不随尺寸变化而变化,另一个位于近红外,与量子点尺寸有一定相关性。这两个发光峰可能分别与电子空穴对在硅/二氧化硅的缺陷态发光以及电子空穴对在纳米硅量子点/界面态的发光相关。2.采用等离子体化学气相沉积技术制备了两种不同非晶硅层厚度的氮化硅/氢化非晶硅/氮化硅三明治结构,研究了不同能量激光退火对薄膜晶化的影响。通过对薄膜样品的拉曼测试分析,发现在激光能量为320mJ时,样品开始晶化,随着能量的提高,晶化程度增加,在340mJ达到最大。根据拉曼晶化峰的偏移,计算得出了纳米硅量子点尺寸分别为2.8nm和4.7nm,表明了三明治结构对形成的纳米硅量子点的尺寸具有限制作用。设计并制备了基于该三明治结构的电致发光器件,在偏压大于10V时,可以在室温下观测到电致发光。发现不同激光能量下晶化后的样品的电致发光强度不同,发光峰位在680nm和720nm附近,分析表明量子限制效应在氮化硅/硅量子点/氮化硅三明治结构的电致发光中起到了重要作用。3.利用PECVD技术在石英衬底上制备了硼掺杂的非晶硅薄膜,通过控制掺杂的浓度、非晶硅薄膜的厚度以及激光诱导晶化的能量,获得了具有高电导率的掺杂纳米晶/微晶硅薄膜,制得的薄膜样品的方块电阻为113Ω/□。进而通过在样品表面放置一维或二维光栅,利用激光诱导晶化,制备了具有图形结构的微晶硅薄膜,并通过AFM技术,分析了不同的激光能量,不同大小的光栅对薄膜上的图形的影响。发现在激光能量低于230mJ时,可以获得具有较清晰图形结构的薄膜材料。更多还原

【Abstract】 Silicon-based photonics and silicon monolithic optoelectronic integrated is currently one of the most attractive topics and how to realize the silicon-based light source is an urgent and changeling problem. So far, many approaches have been developed to overcome the limitations of the bulk silicon material. In order to obtain efficient silicon based light-emitting materials and devices, it is necessary to systematically study the fabrication, microstructure and opto-electronic properties of Si-based light-emitting materials, among them, nanocrystalline silicon is a potential candidate and has been studied in a worldwide range.Based on our previous work, we further developed the laser induced constraint crystalliza-tion technique to crystallize amorphous Silicon (a-Si)/SiO2multilayers and a-Si/SiNx sand-wiched structures grown in plasma enhanced chemical vapor deposition (PECVD) system. Af-ter laser crystallization, nc-Si QDs/SiO2(or SiNx) films were achieved and the dot size can be as small as1.8nm. The electroluminescence was observed from the crystallized samples and the luminescence behaviors have been investigated systematically. We also used the laser crystallization technique to prepared doped nanocrystalline/microcrystalline silicon thin film on quartz substrates with high electrical conductivity and the influences of the doping concen-trations, film thickness and laser fluence were studied and discussed.The main contents and results of this thesis are as follows:1. We fabricated Si quantum dots (QDs)/SiO2multilayers by using KrF excimer laser (248nm) crystallization of amorphous Si/SiO2multilayered structures deposited on ITO coated glass substrates. Raman spectra and transmission electron microscopy demonstrated the formation of Si QDs and the size could be as small as1.8nm. After laser crystallization, Al electrode was evaporated to obtain light emitting devices and the room temperature electroluminescence was detected with applying the DC volt-age above8V on the top gate electrode. The luminescent intensity increased with increasing the applied voltage and the micro-watt light output was achieved. The EL behaviors for samples with different Si dot sizes were studied and it was found that the corresponding external quantum efficiency was significantly enhanced in sample with ultra-small sized Si QDs.2. Amorphous SiN/amorphous Si/amorphous SiN sandwiched structures were prepared by plasma-enhanced chemical vapor deposition. Raman spectra demonstrates the for-mation of Si quantum dots(QDs) with average size of2.8nm and4.7nm when the laser energy is above320mJ and the size can be controlled due to constrained crystal-lization in sandwiched structures. Room temperature electroluminescence (EL) can be detected with applying the DC voltage above10V and effect of laser fluence and size of Si QDs was evaluated. We attribute the EL spectrum peaks at680nm (2.8nm QDs) and720nm (4.7nm QDs) to the radiative recombination of injected electrons and holes within the Si QDs, which is accordance with the quantum confinement mechanism.3. The boron (B)-doped amorphous silicon thin films on quartz substrates were fabricated in PECVD system. After laser crystallization, B-doped nanocrystalline/microcrystalline silicon thin films with high conductivity were obtained by controlling the doping con-centration, thickness, and laser fluence. The sheet resistance of the crystallized thin film is about113Omega/square. Moreover, we obtained patterned microcrystalline silicon films by using one-dimensional or two-dimensional phase-shifting gratings and the surface morphologies were characterized by AFM technique. It was found that the clear patterned structures can be formed on the film surface when the laser energy was below230mJ.更多还原