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arXiv 0705.2163cond-mat.mtrl-sci
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半导体纳米晶体介电响应的紧束缚公式

Tight binding formulation of the dielectric response in semiconductor nanocrystals

F. Trani, D. Ninno, G. Iadonisi

摘要:

我们报告的半导体纳米晶体的电子介电响应的理论推导使用紧束缚框架。扩展到纳米尺度的汉克和Sham方法[物理评论B 12,4501(1975)]开发的散装半导体,我们展示了如何局部场效应可以包括在研究中的限制系统。这个方案的一个很大的优点是,被制定在定域轨道,因此它需要很少的计算资源和时间。半导体纳米晶体的光学和屏蔽性能的应用在这里提出和讨论。计算了InAs(直接带隙)和Si(间接带隙)纳米晶的吸收截面、静态极化率和屏蔽函数,结果与第一性原理计算结果和实验数据吻合较好。我们还表明,本计划使我们能够很容易地超越连续介质模型,基于克劳修斯-莫索蒂方程,这是经常使用的,包括表面极化。我们的计算表明,连续介质模型,结合使用的大小依赖的介电常数,低估了极化率,导致非常强的表面极化场。

英文摘要:

We report on a theoretical derivation of the electronic dielectric response of semiconductor nanocrystals using a tight-binding framework. Extending to the nanoscale the Hanke and Sham approach [Phys. Rev. B 12, 4501 (1975)] developed for bulk semiconductors, we show how local field effects can be included in the study of confined systems. A great advantage of this scheme is that of being formulated in terms of localized orbitals and thus it requires very few computational resources and times. Applications to the optical and screening properties of semiconductor nanocrystals are presented here and discussed. Results concerning the absorption cross section, the static polarizability and the screening function of InAs (direct gap) and Si (indirect gap) nanocrystals compare well to both first principles results and experimental data. We also show that the present scheme allows us to easily go beyond the continuum dielectric model, based on the Clausius-Mossotti equation, which is frequently used to include the nanocrystal surface polarization. Our calculations indicate that the continuum dielectric model, used in conjunction with a size dependent dielectric constant, underestimates the nanocrystal polarizability, leading to exceedingly strong surface polarization fields.

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