杂质对耦合量子点体系Fano效应及热电效应的影响

发布时间：2018-12-13 17:59

【摘要】：近年来,低维纳米结构热电材料成为热电材料研究的一个崭新的起点,实验和理论研究工作都证明热电材料的低维化可以大大的提升材料的热电性能。将热能转换为电能的现象称为热电效应(thermoelectric effect),其中最重要的是温差电现象。由于金属材料的温差电动势很小,只被用作测量温度的温差电偶。半导体材料出现以后,由于可以得到比金属材料大得多的温差电动势,所以,半导体材料具有较高的热电能转换效率。热电优值Z表征热电材料的品质因数。评价一种热电材料的热电转换效率高低的标准可以用热电优值来衡量,大的优值对应热电转换效率较高的器件。电导率G、塞贝克系数S和热导率κ之间的关系是决定热电优值的关键。这三个参量是相互关联的,都与材料的电子结构、载流子的散射和输运特性有关。在经典理论范畴三个参数满足莫特公式(Mott rule)和维德曼-弗朗兹定律(Widemann-Franz law)。很难通过同时调节三个参数而获得较高的热电优值,但是对于低维纳米结构材料来说,这两个定律已不再适用。因而,通过同时调节三个参量而获得较高的热电优值成为可能。近年的理论和实验研究工作都表明采用材料低维化的方式来提高热电材料性能更为有效。量子点是量子效应最为明显的低维结构,蕴涵丰富的量子传输属性。量子点中电子的态密度和小声子对热导的贡献使提高热电优值成为可能。可以预见,量子点器件的连接点是探索低维结构的热电性质的最佳候选者;量子点体系中能量的量子化、库仑振荡以及Fano效应的量子相干输运现象能够导致新奇的热电特征。平行耦合量子点AB干涉器是一种典型的低维结构,可调节参数丰富,通过磁通及门电压的调节可以使体系中产生丰富的量子输运特征。本文利用非平衡态格林函数理论研究了量子点—量子线耦合AB干涉器中以典型的三种不同方式耦合杂质后,体系在磁场和门电压的调解下的Fano效应及体系的热电性质。本文旨在讨论杂质的存在所引起的局域杂质态对体系Fano效应及热电效应的影响,从理论上对体系的线性电导、热功率及热电优值进行数值模拟及分析。研究结果表明Fano干涉决定了体系的热电效应。热电效应仅存在于电导谱的Fano干涉区,Fano干涉效应越显著,体系的热电优值越大。同时发现,杂质耦合在局域态的耦合方式对体系的Fano效应及热电效应的影响最显著,杂质与电极端点共振态的耦合方式对体系的影响非常小。因此,我们期待这些结果可以帮助我们调节杂质对耦合量子点AB干涉器中热电效应的影响。
[Abstract]:In recent years, low-dimensional nanostructured thermoelectric materials have become a new starting point in the study of thermoelectric materials. Experimental and theoretical studies have proved that the low-dimensional thermoelectric materials can greatly improve the thermoelectric properties of the materials. The phenomenon of converting heat energy to electric energy is called thermoelectric effect (thermoelectric effect),). The most important phenomenon is thermoelectric phenomenon. Because the thermoelectric force of metal material is very small, it is used only as thermocouple to measure temperature. After the appearance of semiconductor materials, the thermoelectric energy conversion efficiency of semiconductor materials is higher than that of metal materials because the thermoelectric potential is much larger than that of metal materials. The thermoelectric value Z characterizes the quality factor of thermoelectric material. The standard for evaluating the thermoelectric conversion efficiency of a thermoelectric material can be measured by the thermoelectric value, and the large value corresponds to the device with higher thermoelectric conversion efficiency. The relationship among conductivity G, Seebeck coefficient S and thermal conductivity 魏 is the key to determine the thermoelectric excellence. These three parameters are related to the electronic structure of the material, carrier scattering and transport characteristics. In the classical theory category, three parameters satisfy the Mott formula (Mott rule) and the Widemann-Franz law). Law. It is difficult to obtain higher thermoelectric excellence by adjusting three parameters simultaneously, but these two laws are no longer applicable to low-dimensional nanostructured materials. Therefore, it is possible to obtain higher thermoelectric excellence by adjusting the three parameters simultaneously. The theoretical and experimental studies in recent years show that it is more effective to improve the properties of thermoelectric materials by using low dimensional materials. Quantum dots (QDs) are low-dimensional structures with the most obvious quantum effects, and contain abundant properties of quantum transmission. The density of states of electrons in quantum dots and the contribution of small phonons to thermal conductivity make it possible to improve the thermoelectric excellence. It can be predicted that the junction points of QDs are the best candidates for exploring the thermoelectric properties of low-dimensional structures, and the quantization of energy, the Coulomb oscillation and the quantum coherent transport of Fano effect can lead to novel thermoelectric characteristics. Parallel coupled quantum dot (AB) interferometer is a typical low-dimensional structure with rich adjustable parameters. It can produce rich quantum transport characteristics by adjusting the flux and gate voltage. In this paper, the Fano effect and thermoelectric properties of quantum dot-quantum wire coupled AB interferometer with three different coupling impurity in magnetic field and gate voltage are studied by using the Green's function theory of nonequilibrium state. In this paper, the influence of local impurity states on Fano effect and thermoelectric effect is discussed. The linear conductance, thermal power and thermoelectric excellence of the system are numerically simulated and analyzed theoretically. The results show that Fano interference determines the thermoelectric effect of the system. The thermoelectric effect exists only in the Fano interference region of the conductance spectrum. The more significant the Fano interference effect, the greater the thermoelectric excellence of the system. At the same time, it is found that the coupling mode of impurity coupling in local state has the most significant effect on the Fano effect and thermoelectric effect of the system, and the coupling mode of impurity and electrode terminal resonance has little effect on the system. Therefore, we hope that these results will help us to adjust the influence of impurities on the thermoelectric effect in the coupled quantum dot AB interferometer.
【学位授予单位】：辽宁大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O471.1

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