三元混晶四层系统的表面和界面声子极化激元

运用改进的无规元素等位移模型和玻恩-黄近似,结合电磁场的麦克斯韦方程和边界条件,研究了真空/极性二元晶体薄膜/极性三元混晶薄膜/极性二元晶体衬底四层系统的表面和界面声子极化激元.以AlxGa1-xAs/GaAs和ZnxCd1-xSe/ZnSe为例,获得了表面和界面声子极化激元模的色散关系以及表面模和界面模的频率随混晶组分和薄膜厚度的变化关系.结果表明,三元混晶四层异质结系统中存在七支表面和界面声子极化激元模,且这七支表面模和界面模的频率随混晶组分和薄膜厚度呈非线性变化,三元混晶的"单模"和"双模"性也在色散曲线中得到了很好的体现.     

二维声学极化子的基态能量和有效质量

自陷电子对了解光电材料的光学性质非常重要.近些年来,形变晶格中电子自陷的问题受到研究人员的广泛关注.电子既与声学模耦合,也与光学模相互作用,但电子由自由态向自陷态的转变缘于近程的电子-声学声子耦合.研究表明:声学极化子在大多数半导体以及Ⅲ-Ⅴ族化合物,甚至碱卤化物中都不可能自陷.另一方面,电子-声子耦合在束缚结构,如二维、一维系统中,会有所增强.换言之,电子在低维结构中更容易自陷.Farias等人指出:声学极化子在二维系统中自陷的临界电子-声子耦合常数为定值,不随声子截止波矢的变化而改变.这种结论在物理上不尽合理.通过计算二维系统中的声学极化子基态能量和有效质量,讨论了二维声学极化子自陷问题.研究发现,二维声学极化子自陷转变的临界耦合常数随声子截止波矢的增加朝电子-声子耦合较弱的方向变化.这一特征与前人关于体和表面极化子研究获得的结论定性一致.所得二维声学极化子基态能量的表达式与Farias等人一致,但自陷的结果与Farias等人的结果在定性和定量上均有不同,我们认为Farias等人关于二维声学极化子自陷转变点的确定方式有不妥之处.通过改进自陷转变点的确定方式,得到了在物理上更合理的结果.     

通过形变势弱耦合表面极化子的重整化质量

采用推广的线性组合算符法和拉格郎 日乘子法研究了晶体中电子与SO声子和SA声子均为弱耦合极化子的重整化质量。结果表明,当电子接近晶体表面时,电子和表面声学声子耦合要比电子与表面光学声子的耦合弱。而且都与Debye截止波数有关;当极化子远离晶体表面时,电子－SO声子相互作用和电子－SA声子相互作用对极化子的重整化质量的影响可以不计,这时电子与体声子的相互作用对极化子重整化质量的贡献是主要的。     

声子色散和磁场对极性晶体中极化子自陷能的影响

利用线性组合算符和幺正变换相结合的方法,研究了声子色散和磁场对极性晶体中极化子振动频率和自陷能的影响.计及纵光学(LO)声子色散,在抛物近似下导出了极性晶体中极化子自陷能随电子-纵光学声子耦合常数、回旋共振频率和声子色散系数之间的变化关系.数值计算结果表明极化子自陷能随电子-纵光学声子耦合常数、回旋共振频率和声子色散系数的增大而增大.     

抛物量子阱中束缚极化子的温度效应

理论研究了抛物量子阱中强耦合束缚极化子的温度效应,采用线性组合算符和幺正变换相结合的方法得到了极化子基态能量和基态结合能的表达式.极化子基态能量和基态结合能分别是振动频率、电子-声子耦合强度、库仑束缚势强度、阱宽以及阱深的函数.在有限温度下,电子-声子系统将不再完全处于基态,晶格振动不但激发实声子,同时也使电子受到激发...     

一维分子晶体系统的极化子-孤子压缩态、系统基态性质和量子涨落

基于一维分子晶体系统的 Holstein 模型,采用压缩-相干态展开方法,计及电子-声子间量子关联和重整化平移修正,分析和研究电子-双声子相互作用对极化子-孤子系统基态性质和量子涨落的影响.推导了一维极化子-孤子系统的封闭形式非线性方程.应用非线性项展开方法,给出非线性方程的解析解和相关基态特性结果.研究表明,仅当电子-双声子耦合强度 g₁<0时非线性方程才有孤波解,此时声子量子涨落效应随着压缩的增加,极化子-孤子系统基态能量变得更负,孤子局域减少,孤子态更加稳定;另一方面,电子密度涨落〈Δ²n〉和声子坐标-动量的不确定量〈Δ²p〉〈Δ²q〉比无声子压缩效应的大,极化子结合能变得更负.特别是,当g₁<0时,双声子效应的量子涨落〈Δ²n〉与〈Δ²p〉〈Δ²q〉的值比单声子情况有明显增加. 关键词： 压缩-相干态展开 极化子-孤子态与量子涨落 电子-双声子相互作用 非线性薛定谔方程     

三元混晶的远红外光谱

采用无序元素孤立位移模型(REI mode),建立了三元混晶AB_1-xC_x晶格动力学的Born-Huang方程,并由此出发讨论了几种三元混晶晶格振动的介电常数和远红外反射谱。理论计算结果表明,这个模型适用于三元混晶的所有情况：(1)单模情况——在整个成分比例区域内(0≤x≤1)有1支横光学声子(TO)和1支纵光学声子(LO);(2)双模情况——在整个成分比例区域内(0≤x≤1),有2支横光学声子和2支纵光学声子;(3)第3种情况——部分区域为单模而另外区域为双模。结果显示,单模晶体只有1个反射带;双模晶体有2个反射带;第3种类型的晶体在部分区域有1个反射带而在另外的区域有2个反射带。该理论模型提供了一个理解三元混晶光学性质的可能的途径,依此为基础可以讨论电子-声子相互作用等其他问题。     

声子和温度对球型量子点中极化子性质的影响

采用求解能量本征方程、幺正变换及变分相结合的方法,研究声子和温度对球型量子点中极化子性质的影响.数值计算表明,声子效应导致极化子的基态能量低于电子能量,且极化子基态能量随电子-声子耦合强度的增大而降低.数值计算还表明,当温度较低,使得电子热运动能量小于声子能量时,声子不会被激发,极化子的基态能量不随温度的变化而变化;在温度较高,使得电子热运动能量大于声子能量时,电子和晶格热运动加剧,更多的声子被激发.极化子的基态能量随温度的升高而增大.     

钛酸锶晶体的光致介电常数激增以及超顺电大极化子理论

钙钛矿类化合物钛酸锶具有明显的光致介电增长的性质,这是由于被光激发至Ti⁴⁺的3d能带上的电子具有良好的巡游特性,为了进一步揭示光致介电增长的微观机理,这里假设巡游电子同时与两类声子发生耦合作用,一方面,电子与A_1g模式的晶格呼吸子发生强相互作用,另一方面,电子还与T_1u模式的非简谐声子具有相对较弱的耦合.通过变分法计算可得,这种复杂的电声耦合作用在晶体中形成两种极化子:自陷极化子和超顺电大极化子.正是由于超顺电大极化子的形成,导致了光致介电激增的现象.     

多原子半无限晶体中极化子的激发能量

研究多原子半无限晶体中电子与表面光学SO声子和体纵光学LO声子强耦合的极化子的激发态的性质。采用线性组合算符和幺正变换方法导出强耦合情形下极化子的基态能量、第一内部激发态能量和激发能量。结果表明,多原子半无限晶体中强耦合极化子的基态能量、第一内部激发态能量和激发能量不仅包含不同支LO声子和不同支SO声子与电子耦合的能量,而且还包含不同支LO声子之间和不同支SO声子之间相互作用贡献的附加能量。     

Optical vibration modes and electron－phonon interaction in ternary mixed crystals of polar semiconductors

Optical vibrations of the lattice and the electron－phonon interaction in polar ternary mixed crystals are studied in the framework of the continuum model of Born and Huang and the random-element-isodisplacement model. A normal-coordinate system to describe the optical vibration in ternary mixed crystals is correctly adopted to derive a new Fr?hlich-like Hamiltonian for the electron－phonon interaction including the unit-cell volume variation influence. The numerical results for the phonon modes, the electron－phonon coupling constants and the polaronic energies for several typical materials are obtained. It is verified that the nonlinearity of the electron－phonon coupling effects with the composition is essential and the unit-cell volume effects cannot be neglected for most ternary mixed crystals.     

Cyclotron resonance of polarons in ternary mixed crystals

Rayleigh-Schr?dinger perturbation theory and an improved Wigner-Brillouin perturbation theory has been used to study the cyclotron resonance of the polarons in ternary mixed crystals in the zero-temperature limit. The interaction between an electron and two branches of longitudinal optical phonon modes is taken into account in the framework of the random-element-isodisplacement model. The numerical results for several ternary mixed crystals show that the polaronic cyclotron energy and mass split successively twice related to the higher and lower branches of longitudinal optical phonon modes of ternary mixed crystals. A non-linear dependence of the polaronic cyclotron energy and mass on the composition x is found. Received 19 March 2002 / Received in final form 21 March 2003 Published online 20 June 2003 RID="a" ID="a"e-mail: xxliang@imu.edu.cn     

Exciton--polaritons in ternary mixed crystals

In this paper the bulk exciton polaritons in ternary mixed crystals (TMCs) are investigated in the Born--Huang approximation. The numerical results of the polariton frequencies as functions of the wave-vector and the compositions for ternary mixed crystals Al电震荡 三重混合晶体 激子 电磁学polariton, exciton, ternary mixed crystalProject supported partly by PhD Progress Foundation of Higher Education Institutions of China (Grant No~20040126003) and the Natural Science Foundation of Inner Mongol of China (Grant No~200408020101).2006-10-08In this paper the bulk exciton polaritons in ternary mixed crystals （TMCs） are investigated in the Born-Huang approximation. The numerical results of the polariton frequencies as functions of the wave-vector and the compositions for ternary mixed crystals AlxGa1-xAs, CdxZn1-xSe, and AlxGa1-xN are obtained and discussed. The new dispersion characteristics for exciton-polaritons in TMC systems are found in comparison with binary crystals. The splitting of the two branches of exciton-polariton frequencies varies nonlinearly with the composition of TMCs and has a minimum in the long-wavelength range.     

One and two mode behaviors of surface phonon-polaritons of ternary mixed crystal films

One and two mode behaviors of surface phonon-polaritons of ternary mixed crystal (TMC) films are studied in the framework of the modified random-element-isodisplacement model and the Born-Huang approximation, based on the Maxwell's equations with the usual boundary conditions. The numerical results for the frequencies and splitting energies of the surface phonon-polaritons as functions of the composition in several II-VI and III-V compound semiconductor ternary mixed crystal films are obtained. The “two-mode” and “one-mode” behaviors for different types of systems are clearly shown in the curves of the splitting energies of surface phonon-polaritons. The theoretical conclusion obtained is agreement with the reported experiment results for bulk TMC systems.     

Polaronic effects due to surface optical vibration modes in a freestanding cylindrical wurtzite nanowire

The ground-state polaron self-trapped energy and effective mass due to the surface optical (SO) phonon modes in a freestanding wurtzite GaN nanowire (NW) were studied by means of the Lee–Low–Pines variational approach. Based on the dielectric continuum and Loudon’s uniaxial crystal models, the polar optical phonon modes in the one-dimensional (1D) systems are analyzed, and the vibrating spectra of SO modes and electron–SO phonon coupling functions are discussed and analyzed. The calculations on the ground-state polaron self-trapped energy and correction of effective mass due to the SO phonon modes in the 1D GaN NWs reveal that the polaron self-trapped energy and correction of effective mass are far larger than those in 1D GaAs NW systems. The reasons resulting in this obvious difference in the two 1D structures are mainly due to the different electron–phonon coupling constants and electron effective masses of bulk materials constituting the two types of 1D confined system. Finally, the polaronic properties of the wurtzite 1D GaN NWs have been compared with those of the wurtzite GaN-based two-dimensional quantum wells. The physical origination of these characteristics and their distinction in the different-dimensionality systems has been analyzed in depth.     

Electronic structure and optical properties of CdSexTe1−x mixed crystals

The band structure and optical properties of the CdSe_xTe_1−x ternary mixed crystals have been studied using the pseudopotential formalism under an improved virtual crystal approximation approach. Quantities such as, energy gaps, band-gap bowing parameters, electron effective mass and dielectric constants are calculated. Our results agree well with the available data in the literature. The composition dependence of all studied quantities has been expressed by quadratic polynomial forms.     

Intermediate-coupling polaron in a ternary mixed crystal

The intermediate-coupling polaron in a ternary mixed crystalA _xB_1–x C is studied within the framework of the random-element-isodisplacement (REI) model. The self-trapping energy and effective mass of the polaron are analytically derived in the mono-phonon approximation. The numerical results of the electron-LO phonon coupling constants, self-trapping energies and effective masses of the polarons for several mixed crystal materials are obtained as functions of the compositionx. It is found that there is a minimum of the polaron effects at a intermediatary value of the compositions for either the onemode or two-mode behaviour mixed crystals. The reduction of electron-LO-phonon interaction observed recently in the AgCl _x Br_1–x (0x0.21) mixed crystals can be qualitatively explained by our theoretical results.     

磁场中极性晶体板内的强耦合极化子

采用推广的强耦合变分波函数方法，研究了在板面垂直方向施加磁场的极性晶体板内电子与体纵光学声子和表面光学声子强相互作用系统的能量和有效质量，得出了作为厚度和磁场强度函数的极化子的能量和有效质量表达式．对Cu₂O材料作了数值计算，并讨论极化子的基态能、电子与声子相互作用能以及有效质量随板厚及磁场强度变化的规律 关键词：