發(fā)布時間：2018-12-13 17:59

【摘要】：近年來,低維納米結(jié)構(gòu)熱電材料成為熱電材料研究的一個嶄新的起點,實驗和理論研究工作都證明熱電材料的低維化可以大大的提升材料的熱電性能。將熱能轉(zhuǎn)換為電能的現(xiàn)象稱為熱電效應(yīng)(thermoelectric effect),其中最重要的是溫差電現(xiàn)象。由于金屬材料的溫差電動勢很小,只被用作測量溫度的溫差電偶。半導體材料出現(xiàn)以后,由于可以得到比金屬材料大得多的溫差電動勢,所以,半導體材料具有較高的熱電能轉(zhuǎn)換效率。熱電優(yōu)值Z表征熱電材料的品質(zhì)因數(shù)。評價一種熱電材料的熱電轉(zhuǎn)換效率高低的標準可以用熱電優(yōu)值來衡量,大的優(yōu)值對應(yīng)熱電轉(zhuǎn)換效率較高的器件。電導率G、塞貝克系數(shù)S和熱導率κ之間的關(guān)系是決定熱電優(yōu)值的關(guān)鍵。這三個參量是相互關(guān)聯(lián)的,都與材料的電子結(jié)構(gòu)、載流子的散射和輸運特性有關(guān)。在經(jīng)典理論范疇三個參數(shù)滿足莫特公式(Mott rule)和維德曼-弗朗茲定律(Widemann-Franz law)。很難通過同時調(diào)節(jié)三個參數(shù)而獲得較高的熱電優(yōu)值,但是對于低維納米結(jié)構(gòu)材料來說,這兩個定律已不再適用。因而,通過同時調(diào)節(jié)三個參量而獲得較高的熱電優(yōu)值成為可能。近年的理論和實驗研究工作都表明采用材料低維化的方式來提高熱電材料性能更為有效。量子點是量子效應(yīng)最為明顯的低維結(jié)構(gòu),蘊涵豐富的量子傳輸屬性。量子點中電子的態(tài)密度和小聲子對熱導的貢獻使提高熱電優(yōu)值成為可能�？梢灶A(yù)見,量子點器件的連接點是探索低維結(jié)構(gòu)的熱電性質(zhì)的最佳候選者;量子點體系中能量的量子化、庫侖振蕩以及Fano效應(yīng)的量子相干輸運現(xiàn)象能夠?qū)е滦缕娴臒犭娞卣�。平行耦合量子點AB干涉器是一種典型的低維結(jié)構(gòu),可調(diào)節(jié)參數(shù)豐富,通過磁通及門電壓的調(diào)節(jié)可以使體系中產(chǎn)生豐富的量子輸運特征。本文利用非平衡態(tài)格林函數(shù)理論研究了量子點—量子線耦合AB干涉器中以典型的三種不同方式耦合雜質(zhì)后,體系在磁場和門電壓的調(diào)解下的Fano效應(yīng)及體系的熱電性質(zhì)。本文旨在討論雜質(zhì)的存在所引起的局域雜質(zhì)態(tài)對體系Fano效應(yīng)及熱電效應(yīng)的影響,從理論上對體系的線性電導、熱功率及熱電優(yōu)值進行數(shù)值模擬及分析。研究結(jié)果表明Fano干涉決定了體系的熱電效應(yīng)。熱電效應(yīng)僅存在于電導譜的Fano干涉區(qū),Fano干涉效應(yīng)越顯著,體系的熱電優(yōu)值越大。同時發(fā)現(xiàn),雜質(zhì)耦合在局域態(tài)的耦合方式對體系的Fano效應(yīng)及熱電效應(yīng)的影響最顯著,雜質(zhì)與電極端點共振態(tài)的耦合方式對體系的影響非常小。因此,我們期待這些結(jié)果可以幫助我們調(diào)節(jié)雜質(zhì)對耦合量子點AB干涉器中熱電效應(yīng)的影響。
[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.
【學位授予單位】：遼寧大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：O471.1

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