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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。
Trapped electrons are very important for understanding the optical properties of photovoltaic materials. In recent years, the problem of electron entrapment in deformed lattices has drawn the attention of researchers. Electrons are both coupled to the acoustic mode and to the optical mode, but the transition of the electron from free state to the trapped state is due to the short-range electron-acoustic phonon coupling. Studies have shown that acoustic polarons are not likely to trap in most semiconductors and III-V compounds, even alkali halides. On the other hand, the electron-phonon coupling is enhanced in the bound structures, such as two-dimensional and one-dimensional systems. In other words, electrons are more likely to subside in low-dimensional structures. Farias et al. Point out that the critical electron-phonon coupling constants of acoustic polarons self-trapping in two-dimensional systems are constant and do not change with the change of the wave vector of phonon cutoff. This conclusion is not physically reasonable. By calculating the ground-state energy and effective mass of the acoustic polarons in a two-dimensional system, the two-dimensional acoustic polaron self-trapping problem is discussed. It is found that the critical coupling constant of the two-dimensional acoustic polaron subsidence transition changes with the increase of the phonon cutoff vector toward the weaker direction of electron-phonon coupling. This feature is qualitatively consistent with the conclusions obtained by previous studies on bulk and surface polaron studies. The resulting two-dimensional acoustic polaron ground state energy expression is consistent with Farias et al, but the results of self-trapping and Farias et al results are qualitatively and quantitatively different, we think Farias et al on two-dimensional acoustic polaron Trap transition point to determine the way there are inappropriate. By improving the determination of self-trapping transition points, we obtained physically more reasonable results.