獨立量子阱中聲學極化子及其自陷轉變
發(fā)布時間：2018-08-12 19:26
【摘要】：納米技術快速發(fā)展,極大地推進了人們對低維系統(tǒng)的廣泛研究。據(jù)現(xiàn)有技術,已經(jīng)可以制備出性能良好的量子線、量子阱、量子點等低維半導體量子結構材料。在這些材料中不僅電子受限,而且聲子系也受到調制。這種特殊的結構將導致其與三維體材料在某些性能上有很大的不同,例如：光電材料的光電性質、能量的輸運特性等等。所以對低維半導體量子結構材料的研究具有意義。電子—聲子相互作用是影響低維半導體材料物理性質的因素之一。本文主要研究獨立量子阱中的聲學極化子(由電子—聲學聲子耦合形成)及其自陷轉變。采用Huybrechts變分法,首先求出獨立量子阱中電子—聲學聲子相互作用的哈密頓量,其次對其進行兩次幺正變換,進而引入坐標、動量線性算符,最后求得獨立量子阱中聲學極化子的基態(tài)能量及其一階導數(shù)值,根據(jù)得到的結果探討研究了獨立量子阱中聲學極化子自陷轉變的相關問題。研究結果顯示：獨立量子阱中聲學極化子基態(tài)能量隨著電子—縱聲學聲子耦合常數(shù)的增大而減小,耦合到達某一強度時聲學極化子基態(tài)能量隨電子—縱聲學聲子耦合常數(shù)變化的曲線上出現(xiàn)拐點,此點為電子從自由態(tài)向自陷態(tài)轉變的“轉變點”,并將相應的電子—聲子耦合常數(shù)稱為臨界耦合常數(shù)。當量子阱阱寬一定時,臨界電子—聲子耦合常數(shù)對應拐點的位置隨聲子截止波矢的增大向著電子—聲子耦合較弱的方向移動,而且臨界電子—聲子耦合常數(shù)與聲子截止波矢的乘積趨于一個定值,可以將這個定值當做判斷聲學極化子自陷的判據(jù),用來判別聲學極化子自陷的難易程度。由此斷定獨立量子阱中聲學極化子的自陷難易程度處于二維情況和三維情況之間,而且隨著阱寬的增大,獨立量子阱中聲學極化子自陷的難度在增大。此外發(fā)現(xiàn)獨立量子阱中聲學極化子的自陷轉變,不僅與量子阱結構(阱寬)有關系,而且也與材料自身(拉曼常數(shù))有一定的關系。運用本文計算得到的獨立量子阱中聲學極化子自陷的判斷標準,理論判斷了實際材料中聲學極化子的自陷。結果表明：聲學極化子很難在堿鹵化物和GaN材料的獨立量子阱結構中發(fā)生自陷轉變,但是聲學極化子在AlN材料的獨立量子阱結構中有可能自陷。該研究結果對設計和制造量子阱器件有指導意義。
[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.
【學位授予單位】：山西師范大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：O469;O471.1
本文編號：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.
【學位授予單位】：山西師范大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：O469;O471.1
【參考文獻】
相關期刊論文 前1條
1 于鳳梅;王克強;申朝文;;極化子效應對非對稱量子阱中光吸收系數(shù)的影響(英文)[J];發(fā)光學報;2010年04期
，本文編號：2180111
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