随机光场调控的量子点输运特性研究

发布时间：2018-05-28 18:10

本文选题：量子点 + 电子输运　；参考：《电子科技大学》2016年硕士论文

【摘要】：量子点又被称为“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强的可操控性,如通过控制量子点的尺寸、化学成分和温度,可以来调节其能隙的大小、发光波段等。同时,量子点基于自身独特的性质,具有多种明显的量子效应,如由于量子点电子能级的离散性引起的量子尺寸效应;由于三维受限导致的量子限域效应;以及由于粒子波动性造成的宏观量子隧道效应等等。量子点的各种特殊的性质也使得量子点自被发现以来就有相当广泛的应用,如,在器件方面,量子点可以应用于QD激光器、QD红外探测器等等;在生物医学方面,量子点可以用来进行生物分子标记、作为荧光探针等等。而基于量子点输运性质的研究,又一直都是各界研究的热点。已经发现了的量子点的电子输运特性包括顺序隧穿效应、库仑阻塞效应、Kondo效应、Fano效应以及Aharonov-Bohm效应等。但是一直以来,在量子点输运性质的研究中人们总是把光场的强度当做一个固定值来考虑,而在现实中光场强度会有一定的涨落。因此,在本文中,我们探究了随机光场调控下量子点的电子输运特性。主要内容如下:(1)介绍了量子点现阶段的研究现状,对已经发现了的量子点的输运性质进行了总结梳理。众所周知,对于量子点中的散粒噪声,它只能在非平衡环境下才能被观察到(例如在本文中,我们给系统加偏置电压的情况)。散粒噪声可以为量子点中的电子输运研究提供在输运过程中电导测量中的那些被遗漏的信息,包括能够得到载流子在统计方面的一些性质;能够用来测定出被转移的电荷的单位;能够获得系统内在的一些关于结构方面的信息等等。另一方面,我们可以通过输运过程中电子的相关性来调制散粒噪声的幅值。(2)建立了一个由相干场驱动,随机场调控的二能级量子点系统。假定量子点与随机场之间的相关函数满足Gaussian-Markovian随机过程,其均值为零,且相关函数满足||)()(tttxteDx--???????。其中,D是随机场强度,?是与随机场带宽相关的量。(3)由系统的哈密顿量推导系统的主方程和速率方程,从理论上探究了系统中的电流和散粒噪声。在大偏压下的介观体系中,速率方程方法在一开始就涵盖了非弹性散射、电荷相互作用和与外界耦合等问题;同时它不仅能够解析处理很多问题,而且比其他的方法更简单,更容易理解。因此,在文中我们使用速率方程方法来描述系统顺序隧穿区的电子输运状况。(4)在结果与讨论中,我们发现,随机场的引入可以加强量子点和相干场的共振效应,并引入新的共振点。在共振点,量子点两能级之间的布居数之差被抑制,电流却极大的增强了。同时,电流的零频散粒噪声通过随机场适当的调制,可以在亚泊松和超泊松之间急剧转化。
[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.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O471.1

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