Modeling the compositional dependence of electron diffraction in dilute GaAs- and GaP-based compound semiconductors
Modeling the compositional dependence of electron diffraction in dilute GaAs- and GaP-based compound semiconductors
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模拟稀 GaAs 和 GaP 基化合物半导体中电子衍射的成分依赖性
DOI：
10.1103/physrevb.78.075207
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发表时间：
2008
影响因子：
3.7
通讯作者：
K. Volz
中科院分区：
文献类型：
--
作者：
O. Rubel;I. Nemeth;W. Stolz;K. Volz
从理论上研究了在GaP和GaAs中掺入等价杂质引起的200电子束反射强度的变化。计算是在运动散射理论的框架内进行的。利用密度泛函理论计算的原子形状因子和经验势价力场模型计算了无规合金的结构因子。计算中考虑了电子密度重分布对电子散射幅度的影响，以及与杂质位置有关的局域晶格扭曲的影响。我们提出了一种解析计算这些扭曲的方法，并将它们以一种简单的形式引入结构因子的表达式中。这种方法是模拟的另一种选择，模拟需要对原子松弛进行严格的计算，并且能够在考虑静态原子位移的情况下定量预测稀合金结构因子的成分变化。讨论了这些结果对用暗场透射式电子显微镜定量测量异质结中组分起伏的意义。氮和硼掺杂对200反射强度的影响被它们引起的静态原子位移部分补偿。忽略这一影响将导致对杂质含量的低估约为原来的两倍。研究发现，电子密度的重新分布对化学成分的评估不那么重要，导致200个散射幅度的相对误差约为16%。
The change in the intensity of the 200 electron-beam reflection induced by the incorporation of isovalent impurities in GaAs and GaP is studied theoretically. Calculations are performed in the framework of the kinematical scattering theory. The structure factor of random alloys was obtained using atomic form factors calculated with the density-functional theory and an empirical-potential valence force-field model for the structure relaxation. The calculations include the effect of redistribution of the electron density on the electronscattering amplitudes as well as the effect of the local lattice distortions associated with the impurity sites. We propose a way to calculate these distortions analytically and to introduce them in a simple form to the expression for the structure factor. This method is an alternative to the simulations, which invoke demanding computations for atomic relaxation, and enables quantitative prediction of the compositional variation of the structure factor for dilute alloys taking into account static atomic displacements. The implications of the results for quantification of composition fluctuations in heterostructures using dark-field transmission electron microscopy are discussed. The effect of nitrogen and boron incorporation on the intensity of the 200 reflection is found to be partly compensated by the static atomic displacements they cause. Neglecting this effect would lead to an underestimation of the impurity content by approximately a factor of two. The redistribution of the electron density is found to be less crucial for the evaluation of the chemical composition leading to a relative error in the 200 scattering amplitude of about 16%.