独立量子阱中声学极化子及其自陷转变
发布时间：2018-08-12 19:26
【摘要】：纳米技术快速发展,极大地推进了人们对低维系统的广泛研究。据现有技术,已经可以制备出性能良好的量子线、量子阱、量子点等低维半导体量子结构材料。在这些材料中不仅电子受限,而且声子系也受到调制。这种特殊的结构将导致其与三维体材料在某些性能上有很大的不同,例如：光电材料的光电性质、能量的输运特性等等。所以对低维半导体量子结构材料的研究具有意义。电子—声子相互作用是影响低维半导体材料物理性质的因素之一。本文主要研究独立量子阱中的声学极化子(由电子—声学声子耦合形成)及其自陷转变。采用Huybrechts变分法,首先求出独立量子阱中电子—声学声子相互作用的哈密顿量,其次对其进行两次幺正变换,进而引入坐标、动量线性算符,最后求得独立量子阱中声学极化子的基态能量及其一阶导数值,根据得到的结果探讨研究了独立量子阱中声学极化子自陷转变的相关问题。研究结果显示：独立量子阱中声学极化子基态能量随着电子—纵声学声子耦合常数的增大而减小,耦合到达某一强度时声学极化子基态能量随电子—纵声学声子耦合常数变化的曲线上出现拐点,此点为电子从自由态向自陷态转变的“转变点”,并将相应的电子—声子耦合常数称为临界耦合常数。当量子阱阱宽一定时,临界电子—声子耦合常数对应拐点的位置随声子截止波矢的增大向着电子—声子耦合较弱的方向移动,而且临界电子—声子耦合常数与声子截止波矢的乘积趋于一个定值,可以将这个定值当做判断声学极化子自陷的判据,用来判别声学极化子自陷的难易程度。由此断定独立量子阱中声学极化子的自陷难易程度处于二维情况和三维情况之间,而且随着阱宽的增大,独立量子阱中声学极化子自陷的难度在增大。此外发现独立量子阱中声学极化子的自陷转变,不仅与量子阱结构(阱宽)有关系,而且也与材料自身(拉曼常数)有一定的关系。运用本文计算得到的独立量子阱中声学极化子自陷的判断标准,理论判断了实际材料中声学极化子的自陷。结果表明：声学极化子很难在碱卤化物和GaN材料的独立量子阱结构中发生自陷转变,但是声学极化子在AlN材料的独立量子阱结构中有可能自陷。该研究结果对设计和制造量子阱器件有指导意义。
[Abstract]:The rapid development of nanotechnology has greatly promoted the extensive research on low-dimensional systems. According to the prior art, low dimensional semiconductor quantum structure materials such as quantum wire, quantum well, quantum dot and so on can be prepared. In these materials, not only electrons are limited, but also phonons are modulated. This kind of special structure will lead to a great difference from three-dimensional bulk materials in some properties, such as the photoelectric properties of optoelectronic materials, the transport characteristics of energy, and so on. Therefore, the study of low dimensional semiconductor quantum structure materials is of significance. Electron-phonon interaction is one of the factors affecting the physical properties of low-dimensional semiconductor materials. In this paper, the acoustic polaron (formed by electron-acoustic phonon coupling) and its self-trapping transition in an independent quantum well are studied. By using the Huybrechts variational method, the Hamiltonian of electron-acoustic phonon interaction in an independent quantum well is first obtained, then the unitary transformation is carried out twice, and then the coordinate and momentum linear operator is introduced. Finally, the ground state energy and the first order derivation of acoustic polaron in an independent quantum well are obtained. Based on the obtained results, the problems related to the self-trapping transition of acoustic polaron in an independent quantum well are discussed. The results show that the ground state energy of acoustic polaron decreases with the increase of electron-longitudinal phonon coupling constant in an independent quantum well. When the coupling reaches a certain intensity, there is an inflection point on the curve of the ground state energy of acoustic polaron changing with the electron-longitudinal phonon coupling constant, which is the "transition point" of the electron from the free state to the self-trapped state. The corresponding electron-phonon coupling constant is called the critical coupling constant. When the quantum well width is fixed, the position of the critical electron-phonon coupling constant corresponding to the inflection point moves towards the direction of the weaker electron-phonon coupling with the increase of the phonon cutoff wave vector. Moreover, the product of the critical electron-phonon coupling constant and the phonon cutoff wave vector tends to be a fixed value, which can be used as a criterion to judge the self-trapping of acoustic polaron and to judge the difficulty of acoustic polaron self-trapping. It is concluded that the self-trapping difficulty of acoustic polaron in an independent quantum well is between two-dimensional and three-dimensional conditions, and the difficulty of self-trapping of acoustic polaron in an independent quantum well increases with the increase of well width. It is also found that the self-trapping transition of acoustic polaron in an independent quantum well is related not only to the quantum well structure (well width), but also to the material itself (Raman constant). Based on the criterion of acoustic polaron self-trapping in an independent quantum well calculated in this paper, the self-trapping of acoustic polaron in practical materials is determined theoretically. The results show that the acoustic polaron is difficult to self-trap in the independent quantum well structures of alkali halides and GaN materials, but the acoustic polarons may be self-trapping in the independent quantum well structures of AlN materials. The results are useful for the design and fabrication of quantum well devices.
【学位授予单位】：山西师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O469;O471.1
本文编号：2180111
[Abstract]:The rapid development of nanotechnology has greatly promoted the extensive research on low-dimensional systems. According to the prior art, low dimensional semiconductor quantum structure materials such as quantum wire, quantum well, quantum dot and so on can be prepared. In these materials, not only electrons are limited, but also phonons are modulated. This kind of special structure will lead to a great difference from three-dimensional bulk materials in some properties, such as the photoelectric properties of optoelectronic materials, the transport characteristics of energy, and so on. Therefore, the study of low dimensional semiconductor quantum structure materials is of significance. Electron-phonon interaction is one of the factors affecting the physical properties of low-dimensional semiconductor materials. In this paper, the acoustic polaron (formed by electron-acoustic phonon coupling) and its self-trapping transition in an independent quantum well are studied. By using the Huybrechts variational method, the Hamiltonian of electron-acoustic phonon interaction in an independent quantum well is first obtained, then the unitary transformation is carried out twice, and then the coordinate and momentum linear operator is introduced. Finally, the ground state energy and the first order derivation of acoustic polaron in an independent quantum well are obtained. Based on the obtained results, the problems related to the self-trapping transition of acoustic polaron in an independent quantum well are discussed. The results show that the ground state energy of acoustic polaron decreases with the increase of electron-longitudinal phonon coupling constant in an independent quantum well. When the coupling reaches a certain intensity, there is an inflection point on the curve of the ground state energy of acoustic polaron changing with the electron-longitudinal phonon coupling constant, which is the "transition point" of the electron from the free state to the self-trapped state. The corresponding electron-phonon coupling constant is called the critical coupling constant. When the quantum well width is fixed, the position of the critical electron-phonon coupling constant corresponding to the inflection point moves towards the direction of the weaker electron-phonon coupling with the increase of the phonon cutoff wave vector. Moreover, the product of the critical electron-phonon coupling constant and the phonon cutoff wave vector tends to be a fixed value, which can be used as a criterion to judge the self-trapping of acoustic polaron and to judge the difficulty of acoustic polaron self-trapping. It is concluded that the self-trapping difficulty of acoustic polaron in an independent quantum well is between two-dimensional and three-dimensional conditions, and the difficulty of self-trapping of acoustic polaron in an independent quantum well increases with the increase of well width. It is also found that the self-trapping transition of acoustic polaron in an independent quantum well is related not only to the quantum well structure (well width), but also to the material itself (Raman constant). Based on the criterion of acoustic polaron self-trapping in an independent quantum well calculated in this paper, the self-trapping of acoustic polaron in practical materials is determined theoretically. The results show that the acoustic polaron is difficult to self-trap in the independent quantum well structures of alkali halides and GaN materials, but the acoustic polarons may be self-trapping in the independent quantum well structures of AlN materials. The results are useful for the design and fabrication of quantum well devices.
【学位授予单位】：山西师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O469;O471.1
【参考文献】
相关期刊论文 前1条
1 于凤梅;王克强;申朝文;;极化子效应对非对称量子阱中光吸收系数的影响(英文)[J];发光学报;2010年04期
，本文编号：2180111
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