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题名	若干纳米半导体量子限域效应及其超快光电特性
作者	冯东海
学位类别	博士
答辩日期	2005
授予单位	中国科学院上海光学精密机械研究所
导师	徐至展
关键词	半导体 纳米结构 量子限域效应 飞秒激光 超快动力学
其他题名	Quantum confinement and ultrafast optoelectronic properties in semiconductor nanostructures
中文摘要	随着纳米结构材料制备技术以及超短超强激光技术的迅猛发展，认识纳米结构体系的特殊光电性能，不仅能加深我们对低维材料的了解和认识，而且有重要的高技术应用背景。我们一方面研究各种纳米结构的量子限域性质及其对光学性能的影响；另一方面，利用飞秒激光超快光谱技术研究飞秒激光辐照下半导体纳米薄膜电子激发的瞬态过程、超快载流子弛豫动力学，以及材料的超快结构相变和烧蚀过程。我们所做的工作以及所获得的主要创新性成果归纳如下：1．首次用多带有效质量理论计算了闪锌矿GaN量子点的电子结构，给出了电子、空穴限域能级随量子点尺寸的依赖关系，获得了与实验结果相吻合的理论吸收光谱。2．用有效质量理论研究了Si、3C-SiC量子点的激子能谱结构。在计算中，创新地考虑了导带、价带的各向异性，各向异性将导致简并能级发生分裂。进一步考虑电子、空穴的交换相互作用，简并的激子基态将分裂成三个“暗”态和一个“亮”态。理论计算的“暗”一“亮”分裂能与实验结果吻合的很好。同时，也获得了激子带隙、激子束缚能随量子点尺寸的变化关系。Si量子点的激子带隙与实验结果吻合的非常好。3．首次开展针状3C-SiC纳米线的光致发光研究，室温下观察到了一强的光致发光宽峰结构，峰中心位置在450nm左右。我们用量子尺寸效应解释了发光实验结果。4．创新地运用色散理论研究半导体量子点的极化子特性。绝对零度下，获得了各向异性量子点的第一激发态的极化子修正能较简单的表达式。极化子修正能随着温度的增加而减小，而且对于尺寸越大的量子点温度的影响愈加明显。5．在实验上，我们用瞬态反射率测量技术首次研究了ZnO薄膜的电子激发、材料结构相变以及烧蚀的瞬态过程。观察到了时间尺度小于1ps的结构相变过程。随着激发光强的加大，结构相变时间变短。对不同激发、探测波长所获得结果的异同性给以分析和讨论。另外，我们也测定了烧蚀闭值：分析了烧蚀形貌，讨论了烧蚀斑的干涉环现象。6．实验上研究了ZnO薄膜在高强度激光激发下高密度载流子所致带隙重整的瞬态过程以及高密度载流子的弛豫过程。发现载流子的能量损失速率高达1.5eV/ps，如此高的能量损失速率主要归结于高密度载流子一载流子散射在能量损失过程中起着重要的作用。
英文摘要	With the development of both the fabrication technique of nanostructures and ultrashort pulse laser technology, it's important to know the special opto-electronic properties of nanostructures, which not only helps to know the specialities in low dimensional materials but also has a background of important high-tech application. Firstly we investigate quantum confinement and its effects on the optical properties of nanostructures. Then we use femtosecond ultrafast spectrum technology to investigate ultrafast electron excitation, structural transition and ablation, and carrier relaxation dynamics in semiconductor films under femtosecond laser irradiation. The main works and innovative results are as follow: 1. The first investigation in the electronic structure of zinc-blende GaN quantum dots is conducted in the framework of the multi-band effective mass approximation. The dependence of the energy of electron and hole states on the quantum dot size is presented. The theoretical absorption spectrum of GaN quantum dots is in good agreement with the existing experimental result. 2. We investigate exciton energy states in Si and 3C-SiC quantum dots by using the effective mass theory, with taking account of the conduction and valence band anisotropy for the first time. The degenerate hole and exciton states are partly split by the band anisotropy. Taking account of the exchange interaction, the exciton ground state is further split into three "dark" states and one "bright" state. The theoretical dark-bright splitting energy agrees well with the experimental data. Furthermore, the exciton band gap and binding energy as a function of dot radius are presented both for Si and for 3C-SiC quantum dots. The band gap of Si quantum dots agrees well with the recent experimental results. 3. The first luminescence property in needle-shaped 3C-SiC nanowires is investigated. A strong broad photoluminescence peak located around 450 nm was observed at room temperature, which may be ascribed to quantum size effects of nanomaterials. 4. The polaron property in semiconductor quantum dots is investigated by using the dispersion theory for the first time. At zero temperature, The relatively simple expressions of the polaron energy shift in the first excited state are presented. Calculations show that the polaron energy shift decreases with the increasing temperature, and the temperature effect is more obvious in large quantum dots. 5. For the first time, we investigate the ultrafast process of electron excitation, structural transition and ablation in ZnO films by using transient reflectivity measurements. We observed the structural transition process with time scale less than 1 ps. With the excitation fluence increasing, the times for the structural transition become short. The difference between different excitation wavelength and probe wavelength are discussed. Furthermore, the ablation threshold fluences are determined, and ablation patterns, especially the interference ring in the ablation patterns, are discussed in detail. 6. The transient process of band-gap renormalization and carrier relaxation in ZnO films at high excited carrier densities are investigated. We found the energy relaxation rate of hot electron distribution in ZnO to be approximately 1.5 eV/ps, which is ascribed to the important role played by high excited carrier-carrier scattering.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/15559]
专题	上海光学精密机械研究所_学位论文
推荐引用方式 GB/T 7714	冯东海. 若干纳米半导体量子限域效应及其超快光电特性[D]. 中国科学院上海光学精密机械研究所. 2005.

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