声场作用下ZnO量子点中载流子自旋相干性动力学机理研究

Enhancing carrier spin coherence is very important for improving the performance of semiconductor spintronic devices, which is restricted by the vaguely dynamical mechanisms of the effective increase on the spin relaxation time and spin dephasing time. The structural properties of materials, temperature, device structures, and time-dependent external fields are considered as the crucial factors for the above problems. Based on the nonequilibrium Green's function approach and the diagonalization of effective Hamiltonian, a mathematical model of the fully microscopic kinetic spin Bloch equation is proposed to study the spin dynamics in ZnO quantum dots. The spatial-temporal features of the carrier spin coherence are numerically simulated that are related to structural properties of ZnO quantum dots, temperature, and device structures. The dominated mechanisms of the spin relaxation and spin dephasing are correspondingly discussed and elucidated. Furthermore, a time-dependent piezoelectric potential is used to transport and control the carrier spin as a novel method; and a fully microscopic kinetic spin Bloch equation will be derived for carrier spin dynamics in ZnO quantum dots interacted with the piezoelectric potential. Characteristic parameters of the spin relaxation and spin dephasing are evaluated with the variation of the piezoelectric potential. A novel dynamical mechanism of enhancing carrier spin coherence in ZnO quantum dots is further established, which is used to predict the new spin-related phenomena and laws. This will be very helpful to design and develop novel spintronic devices as a theoretical guidance.

载流子自旋相干性是提高半导体自旋电子器件性能的关键，但如何有效延长自旋弛豫和自旋消相位的动力学机理是制约增强自旋相干性的首要问题，材料结构特性、温度、器件结构和含时外场被认为是重要的影响因素。本申请以非平衡格林函数和哈密顿量对角化方法为基础，结合ZnO量子点的结构特征，建立载流子自旋的全微观自旋动力学Bloch方程数学模型，数值模拟分析出载流子自旋相干性的空时特征与ZnO量子点结构特征、温度和器件结构等之间的关系，从而确定自旋弛豫和自旋消相位的主要机理；考虑压电势控制载流子自旋输运这种新颖方法，进一步建立压电势作用下ZnO量子点中载流子自旋的全微观自旋动力学Bloch方程，计算出自旋弛豫和自旋消相位的特征参量随压电势变化的规律，进而构建出增强ZnO量子点中载流子自旋相干性的动力学新机理，预测压电势作用下在自旋输运与控制过程中产生的新现象、新规律。这为研发新型自旋电子器件提供理论参考。

良好的载流子自旋相干性是对载流子自旋比特进行量子操控的重要基础，探索延长载流子自旋弛豫与自旋消相位时间的内在机理理则对获得足够的操作时间显得非常关键。本课题通过非平衡格林函数和哈密顿量构建为基础，利用戴逊方程，经过推导得到Kadanoff-Baym方程，进一步用广义Kadanoff-Baym假设和等时条件得到抛物线型氧化锌量子阱在马尔科夫近似下的自旋动力学布洛赫方程，并初步定性分析了弛豫机制。结合氧化锌功能材料的最近研究工作，完成了氧化锌薄膜、氧化锌纳米构筑体的理论与实验研究进展全面深入回顾和分析总结。实验初步微纳加工制造了多层膜结构声表面波器件，包括氮化铝声表面波器件、氧化锌/铌酸锂多层膜表面波器件和钽酸锂表面波器件，并表征分析了器件性能提升因素、声波热效应特性和微流体操控特征。在纳米晶合成方面，直接利用铟源和碱性化合物一步合成纳米晶，烧结后的样品结合荧光光谱和X射线光电子能谱分析发现新颖氧化铟纳米晶特殊的缺陷发光特征峰，揭示了氧化铟纳米晶存在特殊施主-受主对跃迁形成的纵向光学声子伴线特征，这使人们对氧化铟纳米晶缺陷理解更加深入。通过热处理不同浓度掺杂铒离子钨酸铅微晶，观察微晶结构、缺陷和发光行为变化，发现退火处理能够不同程度增宽不同浓度掺杂铒离子钨酸铅微晶的带隙。由于结构的深度弛豫和晶体内晶体场变化使得样较长时间陈放后铒离子绿发光带出现了能级合并，这对钨酸铅闪烁体和铒离子固态激光晶体相关研究提供了新认识。项目资助发表论文6篇，撰写并出版著述章节1章，获得西安市科技奖1项，协助参与项目的3名研究生顺利培养毕业，正在指导培养研究生1名。