Department of Chemistry and James Franck Institute, University of Chicago , Chicago, Illinois 60637, United States.
Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
Nano Lett. 2017 Mar 8;17(3):2094-2101. doi: 10.1021/acs.nanolett.7b00481. Epub 2017 Feb 22.
GaAs is one of the most important semiconductors. However, colloidal GaAs nanocrystals remain largely unexplored because of the difficulties with their synthesis. Traditional synthetic routes either fail to produce pure GaAs phase or result in materials whose optical properties are very different from the behavior expected for quantum dots of direct-gap semiconductors. In this work, we demonstrate a variety of synthetic routes toward crystalline GaAs NCs. By using a combination of Raman, EXAFS, transient absorption, and EPR spectroscopies, we conclude that unusual optical properties of colloidal GaAs NCs can be related to the presence of Ga vacancies and lattice disorder. These defects do not manifest themselves in TEM images and powder X-ray diffraction patterns but are responsible for the lack of absorption features even in apparently crystalline GaAs nanoparticles. We introduce a novel molten salt based annealing approach to alleviate these structural defects and show the emergence of size-dependent excitonic transitions in colloidal GaAs quantum dots.
砷化镓是最重要的半导体材料之一。然而，由于其合成困难，胶体砷化镓纳米晶体在很大程度上仍未得到探索。传统的合成途径要么无法产生纯砷化镓相，要么导致材料的光学性质与其作为直接带隙半导体量子点的预期行为非常不同。在这项工作中，我们展示了多种合成晶态砷化镓 NCs 的途径。通过结合拉曼、扩展 X 射线吸收精细结构、瞬态吸收和电子顺磁共振光谱，我们得出结论，胶体砷化镓 NCs 的异常光学性质可能与 Ga 空位和晶格无序的存在有关。这些缺陷在 TEM 图像和粉末 X 射线衍射图谱中并不明显，但即使在明显的晶态砷化镓纳米颗粒中，它们也会导致缺乏吸收特征。我们引入了一种新颖的基于熔融盐的退火方法来减轻这些结构缺陷，并展示了胶体砷化镓量子点中出现的尺寸依赖的激子跃迁。
