Zeng Haotian, Yu Xuezhe, Fonseka H Aruni, Boras Giorgos, Jurczak Pamela, Wang Tao, Sanchez Ana M, Liu Huiyun
Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE, United Kingdom.
Nanotechnology. 2020 Nov 20;31(47):475708. doi: 10.1088/1361-6528/abafd7.
One of the nanowire (NW) characteristics is its preferred elongation direction. Here, we investigated the impact of Si substrate crystal orientation on the growth direction of GaAs NWs. We first studied the self-catalyzed GaAs NW growth on Si (111) and Si (001) substrates. SEM observations show GaAs NWs on Si (001) are grown along four <111> directions without preference on one or some of them. This non-preferential NW growth on Si (001) is morphologically in contrast to the extensively reported vertical <111> preferred GaAs NW growth on Si (111) substrates. We propose a model based on the initial condition of an ideal Ga droplet formation on Si substrates and the surface free energy calculation which takes into account the dangling bond surface density for different facets. This model provides further understanding of the different preferences in the growth of GaAs NWs along selected <111> directions depending on the Si substrate orientation. To verify the prevalence of the model, NWs were grown on Si (311) substrates. The results are in good agreement with the three-dimensional mapping of surface free energy by our model. This general model can also be applied to predictions of NW preferred growth directions by the vapor-liquid-solid growth mode on other group IV and III-V substrates.
纳米线（NW）的特性之一是其择优生长方向。在此，我们研究了硅衬底晶体取向对砷化镓纳米线生长方向的影响。我们首先研究了在硅（111）和硅（001）衬底上自催化生长砷化镓纳米线的情况。扫描电子显微镜观察表明，硅（001）上的砷化镓纳米线沿四个<111>方向生长，对其中任何一个或某些方向没有择优性。硅（001）上这种非择优的纳米线生长在形态上与广泛报道的硅（111）衬底上垂直<111>择优生长的砷化镓纳米线形成对比。我们基于硅衬底上理想镓液滴形成的初始条件以及考虑不同晶面悬空键表面密度的表面自由能计算，提出了一个模型。该模型进一步解释了根据硅衬底取向，砷化镓纳米线沿选定<111>方向生长时不同的择优情况。为了验证该模型的普遍性，在硅（311）衬底上生长了纳米线。结果与我们模型的表面自由能三维映射结果高度吻合。这个通用模型还可以应用于预测通过气-液-固生长模式在其他IV族和III-V族衬底上纳米线的择优生长方向。
