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首页> 外文期刊>Physical review >Computational study of phonon modes in short-period AlN/GaN superlattices
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Computational study of phonon modes in short-period AlN/GaN superlattices

机译：短周期AlN / GaN超晶格中声子模的计算研究

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摘要

The phonons and infrared absorption of short period [0001] superlattices (AlN)_n(GaN)_(8-n), with n=3,4,5 were calculated by using the density-functional perturbation theory in the local-density approximation. The nature of the modes is discussed in terms of quantum confinement and interface localized modes. The spectrum for e-symmetry modes shows two TO peaks, of which the lowest corresponds to two closely spaced modes confined each near one half of the GaN part of the cell, and the higher one to two closely spaced A1N like modes with one mode localized at the interface showing the strongest oscillator strength and a bulklike LO-TO splitting. For a_1 symmetry, in contrast, a GaN vibration type mode localized near the interface shows the strongest LO-TO splitting and oscillator strength, while two higher modes are found to be only weakly localized in the A1N part of the cell. Lattice constant relaxation of free-standing superlattices leads to a decreasing lattice constant with increasing number of A1N layers and hence an overall increase in phonon frequencies. Qualitative agreement with experimental data is found for the e symmetry but quantitative discrepancies exist and are interpreted as evidence of a different strain state in the experiment.
机译：利用局部密度近似中的密度泛函微扰理论，计算了短周期[0001]超晶格（AlN）_n（GaN）_（8-n）的声子和红外吸收。 。根据量子限制和界面局部化模式讨论了模式的性质。电子对称模式的频谱显示了两个TO峰，其中最低峰对应于两个紧密间隔的模式，每个模式都限制在单元GaN部分的一半附近，而较高的1-2个紧密间隔的AlN类似模式，其中一个模式局部化在界面上显示出最强的振荡器强度和类似LO-TO的体积分裂。相反，对于a_1对称性，位于界面附近的GaN振动型模式显示出最强的LO-TO分裂和振荡器强度，而发现两个较高的模式仅弱地位于单元的AlN部分中。自支撑超晶格的晶格常数弛豫会导致随AlN层数的增加而降低的晶格常数，从而导致声子频率的整体升高。 e对称性与实验数据定性一致，但存在定量差异，并被解释为实验中不同应变状态的证据。

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