Theory of local electric polarization and its relation to internal strain: Impact on polarization potential and electronic properties of group-III nitrides
Theory of local electric polarization and its relation to internal strain: Impact on polarization potential and electronic properties of group-III nitrides
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DOI：
10.1103/physrevb.88.214103
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发表时间：
2013-12-03
影响因子：
3.7
通讯作者：
O'Reilly, Eoin P.
中科院分区：
文献类型：
--
作者：
Caro, Miguel A.;Schulz, Stefan;O'Reilly, Eoin P.
我们提出了晶体固体中的局部电极化理论，并将其应用于研究纤锌矿 III 族氮化物的情况。我们证明，在原子位点评估的电极化的局部值可以根据最近邻距离和玻恩有效电荷的总和来计算。在该模型中，局部极化与内部应变有直接关系，并且可以用内部应变参数来表示。本理论的预测与测试案例 CuPt 类 InGaN 合金和具有随机放置阳离子的 InGaN 超级电池的随机变形的正式 Berry 相计算非常一致。虽然目前的理论水平适用于高离子化合物，例如 III-N 材料，但我们表明，对于较少离子材料，例如 GaAs，需要更复杂的模型，其中必须考虑玻恩有效电荷的应变依赖性。此外，我们还提供了 GaN、InN 和 AlN 的从头算参数，包括压电系数和自发极化的混合函数值，我们用它来准确地实现局部理论表达式。为了计算局部极化电位，我们还提出了点偶极子方法。该方法克服了通过求解原子网格上的泊松方程获得局部势时出现的与离散化和分辨率相关的一些限制。最后，我们进行紧束缚超晶胞计算，以评估合金波动引起的局部极化电位对 InGaN 合金电子性能的影响。特别是，我们发现 InGaN 价带边缘成分的大向上弯曲受到局部极化效应的强烈影响。此外，我们的分析使我们能够提取能隙以及价带和导带边缘的与成分相关的弯曲参数。
We present a theory of local electric polarization in crystalline solids and apply it to study the case of wurtzite group-III nitrides. We show that a local value of the electric polarization, evaluated at the atomic sites, can be cast in terms of a summation over nearest-neighbor distances and Born effective charges. Within this model, the local polarization shows a direct relation to internal strain and can be expressed in terms of internal strain parameters. The predictions of the present theory show excellent agreement with a formal Berry-phase calculation for random distortions of a test-case CuPt-like InGaN alloy and InGaN supercells with randomly placed cations. While the present level of theory is appropriate for highly ionic compounds, such as III-N materials, we show that a more complex model is needed for less ionic materials, such as GaAs, in which the strain dependence of Born effective charges has to be taken into account. Moreover, we provide ab initio parameters for GaN, InN, and AlN, including hybrid functional values for the piezoelectric coefficients and the spontaneous polarization, which we use to accurately implement the local theory expressions. In order to calculate the local polarization potential, we also present a point dipole method. This method overcomes several limitations related to discretization and resolution which arise when obtaining the local potential by solving Poisson's equation on an atomic grid. Finally, we perform tight-binding supercell calculations to assess the impact of the local polarization potential arising from alloy fluctuations on the electronic properties of InGaN alloys. In particular, we find that the large upward bowing with composition of the InGaN valence-band edge is strongly influenced by local polarization effects. Furthermore, our analysis allows us to extract composition-dependent bowing parameters for the energy gap and valence-and conduction-band edges.