本文選題：量子點 + 電子輸運�。� 參考：《電子科技大學》2016年碩士論文

【摘要】：量子點又被稱為“人造原子”,它具有原子物理的一些基本特征,但相比于原子具有更強的可操控性,如通過控制量子點的尺寸、化學成分和溫度,可以來調節(jié)其能隙的大小、發(fā)光波段等。同時,量子點基于自身獨特的性質,具有多種明顯的量子效應,如由于量子點電子能級的離散性引起的量子尺寸效應;由于三維受限導致的量子限域效應;以及由于粒子波動性造成的宏觀量子隧道效應等等。量子點的各種特殊的性質也使得量子點自被發(fā)現(xiàn)以來就有相當廣泛的應用,如,在器件方面,量子點可以應用于QD激光器、QD紅外探測器等等;在生物醫(yī)學方面,量子點可以用來進行生物分子標記、作為熒光探針等等。而基于量子點輸運性質的研究,又一直都是各界研究的熱點。已經發(fā)現(xiàn)了的量子點的電子輸運特性包括順序隧穿效應、庫侖阻塞效應、Kondo效應、Fano效應以及Aharonov-Bohm效應等。但是一直以來,在量子點輸運性質的研究中人們總是把光場的強度當做一個固定值來考慮,而在現(xiàn)實中光場強度會有一定的漲落。因此,在本文中,我們探究了隨機光場調控下量子點的電子輸運特性。主要內容如下:(1)介紹了量子點現(xiàn)階段的研究現(xiàn)狀,對已經發(fā)現(xiàn)了的量子點的輸運性質進行了總結梳理。眾所周知,對于量子點中的散粒噪聲,它只能在非平衡環(huán)境下才能被觀察到(例如在本文中,我們給系統(tǒng)加偏置電壓的情況)。散粒噪聲可以為量子點中的電子輸運研究提供在輸運過程中電導測量中的那些被遺漏的信息,包括能夠得到載流子在統(tǒng)計方面的一些性質;能夠用來測定出被轉移的電荷的單位;能夠獲得系統(tǒng)內在的一些關于結構方面的信息等等。另一方面,我們可以通過輸運過程中電子的相關性來調制散粒噪聲的幅值。(2)建立了一個由相干場驅動,隨機場調控的二能級量子點系統(tǒng)。假定量子點與隨機場之間的相關函數(shù)滿足Gaussian-Markovian隨機過程,其均值為零,且相關函數(shù)滿足||)()(tttxteDx--???????。其中,D是隨機場強度,?是與隨機場帶寬相關的量。(3)由系統(tǒng)的哈密頓量推導系統(tǒng)的主方程和速率方程,從理論上探究了系統(tǒng)中的電流和散粒噪聲。在大偏壓下的介觀體系中,速率方程方法在一開始就涵蓋了非彈性散射、電荷相互作用和與外界耦合等問題;同時它不僅能夠解析處理很多問題,而且比其他的方法更簡單,更容易理解。因此,在文中我們使用速率方程方法來描述系統(tǒng)順序隧穿區(qū)的電子輸運狀況。(4)在結果與討論中,我們發(fā)現(xiàn),隨機場的引入可以加強量子點和相干場的共振效應,并引入新的共振點。在共振點,量子點兩能級之間的布居數(shù)之差被抑制,電流卻極大的增強了。同時,電流的零頻散粒噪聲通過隨機場適當?shù)恼{制,可以在亞泊松和超泊松之間急劇轉化。
[Abstract]:Quantum dots, also known as "artificial atoms," have some basic features of atomic physics, but they are more maneuverable than atoms. For example, by controlling the size, chemical composition and temperature of quantum dots, the size of their energy gaps can be adjusted. A luminous band, etc. At the same time, quantum dots, based on their own unique properties, have many obvious quantum effects, such as the quantum size effect caused by the dispersion of the electron energy levels of quantum dots, the quantum limited effect caused by three-dimensional confinement, and the quantum size effect caused by the dispersion of the electron level of the quantum dot. And the macroscopic quantum tunneling effect caused by particle fluctuation and so on. Because of the special properties of quantum dots, quantum dots have been widely used since they were discovered. For example, quantum dots can be used in QD lasers, QD infrared detectors and so on. Quantum dots can be used to label biomolecules, as fluorescent probes, and so on. The research based on the transport properties of quantum dots has always been a hot topic. The electron transport properties of quantum dots have been discovered, including sequential tunneling effect, Coulomb blocking effect, Aharonov-Bohm effect and so on. However, in the study of the transport properties of quantum dots, the intensity of the light field is always considered as a fixed value, but in reality, the intensity of the light field will fluctuate to a certain extent. Therefore, in this paper, we investigate the electron transport properties of quantum dots controlled by random light field. The main contents are as follows: (1) the present research status of quantum dots is introduced, and the transport properties of quantum dots are summarized. It is well known that the particle noise in a quantum dot can only be observed in a non-equilibrium environment (for example, in this paper, we apply bias voltage to the system). Granular noise can provide the missing information in the measurement of conductance in quantum dots, including the statistical properties of carriers. The unit used to measure the transferred charge; the ability to obtain some information about the structure of the system and so on. On the other hand, we can modulate the amplitude of granular noise by the correlation of electrons in the transport process.) A two-level quantum dot system driven by coherent field and controlled by random field is established. It is assumed that the correlation function between quantum dots and random fields satisfies the Gaussian-Markovian stochastic process, the mean value of which is zero, and the correlation function satisfies the requirements of the Gaussian-Markovian random process. Where D is a random field intensity? The main equation and the rate equation of the system are derived from the Hamiltonian of the system. The current and the shot noise in the system are studied theoretically. In mesoscopic systems with large biases, the rate equation method covers inelastic scattering, charge interaction and coupling with the outside world at the outset, and it not only resolves many problems, but also is simpler than other methods. Easier to understand. Therefore, in this paper, we use the rate equation method to describe the electron transport in the sequential tunneling region of the system. In our results and discussions, we find that the resonance effect of quantum dots and coherent fields can be enhanced with the introduction of the field. A new resonance point is introduced. At the resonance point, the population difference between the two levels of the quantum dot is suppressed, but the current is greatly enhanced. At the same time, the zero-frequency granular noise of the current can be rapidly transformed between sub-Poisson and hyper Poisson by the proper modulation of the random field.
【學位授予單位】：電子科技大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：O471.1

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