Cao Boxiao, Chen Shunda, Jin Xiaochen, Liu Jifeng, Li Tianshu
Department of Civil and Environmental Engineering, George Washington University, Washington, DC 20052, United States.
Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755, United States.
ACS Appl Mater Interfaces. 2020 Dec 23;12(51):57245-57253. doi: 10.1021/acsami.0c18483. Epub 2020 Dec 11.
Group IV alloys have been long viewed as homogeneous random solid solutions since perceiving them as Si-compatible, direct-band gap semiconductors 30 years ago. Such a perception underlies the understanding, interpretation, and prediction of alloys' properties. However, as the race to create scalable and tunable device materials enters a composition domain far beyond the alloys' equilibrium solubility, a fundamental question emerges as to how random these alloys truly are. Here, we show, by combining statistical sampling and large-scale calculations, that GeSn alloy, a promising group IV alloy for mid-infrared technology, exhibits a clear short-range order for solute atoms within its entire composition range. Such a short-range order is further found to substantially affect the electronic properties of GeSn. We demonstrate that the proper inclusion of this short-range order through canonical sampling can lead to a significant improvement over previous predictions on alloy's band gaps by showing an excellent agreement with experiments within the entire studied composition range. Our finding thus not only calls for an important revision of the current structural model for group IV alloy but also suggests that short-range order may generically exist in different types of alloys.
自30年前将IV族合金视为与硅兼容的直接带隙半导体以来，它们长期以来一直被视为均匀的随机固溶体。这种认知是理解、解释和预测合金性能的基础。然而，随着开发可扩展且可调谐的器件材料的竞争进入一个远远超出合金平衡溶解度的成分领域，一个基本问题出现了，即这些合金到底有多随机。在这里，我们通过结合统计抽样和大规模计算表明，锗锡合金（一种用于中红外技术的有前途的IV族合金）在其整个成分范围内溶质原子呈现出明显的短程有序。进一步发现这种短程有序会显著影响锗锡合金的电子性能。我们证明，通过规范抽样适当纳入这种短程有序，可以在整个研究的成分范围内与实验结果达成极佳的一致性，从而比之前对合金带隙的预测有显著改进。因此，我们的发现不仅要求对当前IV族合金的结构模型进行重要修订，还表明短程有序可能普遍存在于不同类型的合金中。
