同质异相的纳米硫化镉的激子复合动力学和自旋极化机制研究

发布时间：2018-01-19 10:31

本文关键词： 硫化镉纳米同质异相激子复合自旋极化　出处：《吉林大学》2016年博士论文　论文类型：学位论文

【摘要】：纳米硫化镉的同质异相转变引起电子结构的改变,影响相应的激子复合动力学和自旋极化机制。激子复合动力学可以探测激子寿命和对应的弛豫或者复合路径,进而理解其相应的电子结构。在室温下制备具有高自旋极化率的材料,为发展自旋半导体器件奠定了基础。尺寸的变化会影响激子的束缚状态,能带结构和材料的磁畴结构,影响着激子动力学和自旋极化率。掺杂可以改变半导体中载流子的种类并引入杂质能级进而改变激子复合的路径和自旋极化产生的机制。高压引起的结构相变改变相邻原子间电子轨道的交叠程度,引起电子结构的变化,为研究不同结构的激子复合动力学和自旋极化率提供了一种有效的手段。作为一种典型和重要的半导体,CdS半导体有着独特的光学性质和丰富有趣的结构,为研究同质异相的激子复合动力学和自旋极化机制提供了机遇。本文主要内容包括:利用气雾化学反应方法制备出了8-10nm的纤锌矿纯CdS和不同Y掺杂浓度的CdS:Y半导体纳米颗粒。以纤锌矿纯CdS样品为初始材料,在5.2GPa和温度分别是150℃和300℃条件下,合成出了闪锌矿和岩盐矿CdS纳米颗粒(8-10nm)。以0.18atom%纤锌矿CdS:Y纳米颗粒(8-10nm)为初始材料,在5.2GPa和300℃条件下,合成出0.20atom%岩盐矿CdS:Y纳米颗粒(8-10nm)。并且这些相在常温常压下稳定保留。纤锌矿、闪锌矿和岩盐矿纯CdS纳米颗粒三个样品的光致发光实验研究表明:和纤锌矿CdS初始样品相比,同质异相转变后的发光强度都显著增强;闪锌矿和岩盐矿CdS纳米颗粒的带边发射峰相比于纤锌矿样品分别显示出蓝移和红移,表明同质异相转变后的闪锌矿样品的带隙增大而岩盐矿的缩小。其带边发射峰位置的荧光寿命探测表明:纤锌矿、闪锌矿和岩盐矿样品的带边辐射衰变寿命分为6.167ns、8.027ns和19.325ns。纤锌矿、闪锌矿和岩盐矿CdS三个结构体系的能带结构和激子复合路径分析表明:与直接带隙半导体纤锌矿和闪锌矿CdS的激子直接复合过程相比,间接带隙半导体岩盐矿CdS的激子间接复合过程多了额外的声子参与,导致了岩盐矿CdS半导体纳米颗粒具有最长的带边辐射衰变寿命。纤锌矿和闪锌矿CdS结构的三维重叠积分别为0.552和0.063,导致纤锌矿CdS结构中电子空穴对的复合较容易发生,带边辐射衰变寿命也较短,与荧光寿命测试结果相符。磁滞回线和磁相变过程分析可知:纤锌矿CdS:Y纳米颗粒的饱和磁化强度随着Y掺杂浓度的增加呈现出先增加后降低的趋势,铁磁转变温度大于380K,Y掺杂有利于提高样品的铁磁转变温度;0.18atom%纤锌矿和0.20atom%岩盐矿CdS:Y在10K的饱和磁化强度分别为0.031emu/g和0.210emu/g,以及在380K分别为0.023emu/g和0.107emu/g,这两个样品的铁磁转变温度都高于380K。纤锌矿和岩盐矿CdS:Y体系的磁性来源分析表明,这两种结构体系的自旋极化主要来自于Cd空位的贡献,没有Y掺杂的贡献;纤锌矿CdS:Y体系的缺陷形成能和自旋组态分析表明,Y掺杂可降低Cd空位缺陷的形成能和自旋组态,综合导致了实验中纤锌矿CdS:Y样品的饱和磁化强度随Y掺杂含量的增加呈现出先增加后降低的趋势;纤锌矿和岩盐矿CdS:Y体系的自旋组态和自旋密度分析表明,Cd空位缺陷在岩盐矿CdS可以形成更高的自旋组态和自旋密度;有两个Cd空位缺陷的纤锌矿和岩盐矿CdS体系的自旋平行与反平行排列状态下系统的总能量差值分别为116.220meV和103.083meV,表明这两个结构体系均具有室温铁磁性,且纤锌矿体系的铁磁转变温度更高。因此,同质异相纳米CdS的激子复合动力学和自旋极化机制研究,对于新一代自旋光电子半导体器件的研究具有一定的指导意义。
[Abstract]:Nano CDs with different phase change caused by electronic structure changes affect the exciton dynamics and spin polarization mechanism. Exciton recombination dynamics can detect the exciton lifetime and the corresponding relaxation or composite path, and then understand the electronic structure. The preparation of materials with high spin polarization at room temperature, which the foundation for the development of semiconductor devices. The spin size changes will affect the bound exciton state, domain structure, band structure and material, affect the exciton dynamics and spin polarization. Doping can change the type of flow carrier in semiconductor and introduces the mechanism of impurity level and change the path and the spin polarized excitons generated. Phase transition high pressure changes caused by the overlapping degree between adjacent atoms in the electron orbits, caused by changes in the electronic structure, for the exciton recombination dynamics research of different structure Provides an effective means and spin polarization. As a typical and important semiconductor, semiconductor CdS have unique optical properties and interesting structure, provides opportunities for the study of homogeneous phase of the exciton recombination dynamics and spin polarization mechanism. The main contents include: the use of aerosol chemical reaction method preparation of CdS:Y semiconductor nanoparticles of pure wurtzite CdS and 8-10nm with different Y doping concentration. The pure wurtzite CdS samples as initial materials, 5.2GPa and temperature were 150 degrees and 300 degrees under the conditions of synthesized sphalerite and rocksalt CdS nanoparticles (8-10nm). The 0.18atom% wurtzite mine CdS:Y nanoparticles (8-10nm) as initial materials, in 5.2GPa and 300 DEG C, the synthesis of 0.20atom% rock salt CdS:Y nanoparticles (8-10nm). And keep stable under normal temperature and pressure. These are wurtzite, zinc ore and rock salt mine Three samples of pure CdS nanoparticles photoluminescence experiments show that compared with the wurtzite CdS initial sample, the luminescence intensity with different phase change after significantly enhanced; sphalerite and rock salt CdS nanoparticles band edge emission compared to the sample wurtzite showed blue and red shift, shown out of phase after the change of sphalerite sample band gap increases while the rock salt mine. The narrow band edge emission peak position of the fluorescence lifetime detection showed that the wurtzite and zinc blende and rock salt samples with boundary radiation decay lifetime is divided into 6.167ns, 8.027ns and 19.325ns. wurtzite, band structure and path analysis showed that the exciton recombination three structure of sphalerite and rock salt CdS: compared with the exciton direct band gap semiconductor of wurtzite and zinc blende CdS direct composite process, indirect exciton band gap semiconductor rocksalt CdS indirect composite process of extra Phonon participation, led to the rocksalt CdS semiconductor nano particles with band edge radiative decay of the longest life. 3D overlap integral wurtzite and zincblende structure of CdS are 0.552 and 0.063, resulting in Wurtzite CdS structure in the recombination of electron hole pairs occur more easily, with side radiation decay of life is also short. And the fluorescence lifetime testing results. The hysteresis loop and magnetic phase transition analysis: wurtzite CdS:Y nanoparticles saturation magnetization with the increase in the concentration of Y increased after decreased, the ferromagnetic transition temperature is greater than 380K, Y doping can improve the ferromagnetic transition temperature of samples; wurtzite 0.18atom% 0.20atom% and CdS:Y in rock salt 10K saturation magnetization were 0.031emu/g and 0.210emu/g, and 380K were 0.023emu/g and 0.107emu/g, the ferromagnetic transition temperature of the two samples was higher than that of wurtzite 380K. and Magnetic source rock salt mine CdS:Y system analysis shows that the spin polarization of these two kinds of structure system mainly comes from the contribution of the Cd vacancy, no Y doping contribution; energy and spin configuration analysis indicate the formation of defects of wurtzite CdS:Y system, formation energy and the spin configuration of Y doped Cd can reduce the vacancy defects, led to the synthesis of wurtzite CdS:Y sample saturation magnetization with increasing Y doping concentration increased first increased and then decreased; spin configuration and spin density of wurtzite and rocksalt CdS:Y system analysis shows that the Cd vacancy defects in rock salt mine CdS can form a spin configuration and spin density higher spin; two the Cd vacancy defects of wurtzite and rocksalt CdS system for parallel and anti parallel alignment total energy difference condition were 116.220meV and 103.083meV, indicating that these two structures are ferromagnetic at room temperature In addition, the ferromagnetic transition temperature of wurtzite system is higher. Therefore, the study of the excitonic recombination dynamics and spin polarization mechanism of homogeneous CdS nanoparticles is of guiding significance for the research of the new generation of spin optoelectronic semiconductor devices.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O469

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