SUPA School of Physics and Astronomy, Room 402, University of Glasgow, Glasgow G12 8QQ, UK.
Ultramicroscopy. 2012 Jul;118:53-60. doi: 10.1016/j.ultramic.2012.05.001. Epub 2012 May 14.
High angle annular dark field (HAADF) image simulations were performed on a series of AlAs/GaAs interfacial models using the frozen-phonon multislice method. Three general types of models were considered-perfect, vicinal/sawtooth and diffusion. These were chosen to demonstrate how HAADF image measurements are influenced by different interfacial structures in the technologically important III-V semiconductor system. For each model, interfacial sharpness was calculated as a function of depth and compared to aberration-corrected HAADF experiments of two types of AlAs/GaAs interfaces. The results show that the sharpness measured from HAADF imaging changes in a complicated manner with thickness for complex interfacial structures. For vicinal structures, it was revealed that the type of material that the probe projects through first of all has a significant effect on the measured sharpness. An increase in the vicinal angle was also shown to generate a wider interface in the random step model. The Moison diffusion model produced an increase in the interface width with depth which closely matched the experimental results of the AlAs-on-GaAs interface. In contrast, the interface width decreased as a function of depth in the linear diffusion model. Only in the case of the perfect model was it possible to ascertain the underlying structure directly from HAADF image analysis.
采用冻结声子多晶面法对一系列 AlAs/GaAs 界面模型进行了高角度环形暗场（HAADF）图像模拟。考虑了三种一般类型的模型-完美、斜面/锯齿和扩散。这些模型被选择用来演示 HAADF 图像测量如何受到技术上重要的 III-V 半导体系统中不同界面结构的影响。对于每个模型，都计算了界面锐度作为深度的函数，并与两种类型的 AlAs/GaAs 界面的像差校正 HAADF 实验进行了比较。结果表明，对于复杂的界面结构，HAADF 成像测量的锐度以复杂的方式随厚度而变化。对于斜面结构，首先揭示了探针穿透的材料类型对测量的锐度有显著影响。还表明，斜面角的增加会在随机台阶模型中产生更宽的界面。Moison 扩散模型产生的界面宽度随深度增加，与 AlAs 在 GaAs 上的界面的实验结果非常吻合。相比之下，线性扩散模型中界面宽度随深度减小。只有在完美模型的情况下，才有可能直接从 HAADF 图像分析确定潜在结构。
