Pura J L, Periwal P, Baron T, Jiménez J
GdS Optronlab, Dpt. Física de la Materia Condensada, ed. LUCIA Universidad de Valladolid, Paseo de Belén 19, E-47011 Valladolid, Spain.
Nanotechnology. 2018 Aug 31;29(35):355602. doi: 10.1088/1361-6528/aaca74. Epub 2018 Jun 5.
The vapour-liquid-solid (VLS) method is by far the most extended procedure for bottom-up nanowire growth. This method also allows for the manufacture of nanowire axial heterojunctions in a straightforward way. To do this, during the growth process, precursor gases are switched on/off to obtain the desired change in the nanowire composition. Using this technique, axially heterostructured nanowires can be grown, which are crucial for the fabrication of electronic and optoelectronic devices. SiGe/Si nanowires are compatible with complementary metal oxide semiconductor (CMOS) technology, which improves their versatility and the possibility of integration with current electronic technologies. Abrupt heterointerfaces are fundamental for the development and correct operation of electronic and optoelectronic devices. Unfortunately, the VLS growth of SiGe/Si heterojunctions does not provide abrupt transitions because of the high solubility of group IV semiconductors in Au, with the corresponding reservoir effect that precludes the growth of sharp interfaces. In this work, we studied the growth dynamics of SiGe/Si heterojunctions based on already developed models for VLS growth. A composition map of the Si-Ge-Au liquid alloy is proposed to better understand the impact of the growing conditions on the nanowire growth process and the heterojunction formation. The solution of our model provides heterojunction profiles that are in good agreement with the experimental measurements. Finally, an in-depth study of the composition map provides a practical approach to the drastic reduction of heterojunction abruptness by reducing the Si and Ge concentrations in the catalyst droplet. This converges with previous approaches, which use catalysts aiming to reduce the solubility of the atomic species. This analysis opens new paths to the reduction of heterojunction abruptness using Au catalysts, but the model can be naturally extended to other catalysts and semiconductors.
气-液-固（VLS）法是目前用于自下而上生长纳米线的最广泛使用的方法。该方法还能以直接的方式制造纳米线轴向异质结。为此，在生长过程中，前驱体气体被打开或关闭，以实现纳米线组成的期望变化。使用这种技术，可以生长轴向异质结构的纳米线，这对于制造电子和光电器件至关重要。硅锗/硅纳米线与互补金属氧化物半导体（CMOS）技术兼容，这提高了它们的通用性以及与当前电子技术集成的可能性。陡峭的异质界面对于电子和光电器件的开发及正确运行至关重要。不幸的是，由于IV族半导体在金中的高溶解度以及相应的储存效应，阻止了尖锐界面的生长，硅锗/硅异质结的VLS生长无法提供陡峭的转变。在这项工作中，我们基于已开发的VLS生长模型研究了硅锗/硅异质结的生长动力学。提出了硅-锗-金液态合金的成分图，以更好地理解生长条件对纳米线生长过程和异质结形成的影响。我们模型的解提供了与实验测量结果高度一致的异质结轮廓。最后，对成分图的深入研究提供了一种切实可行的方法，即通过降低催化剂液滴中的硅和锗浓度来大幅降低异质结的陡峭程度。这与之前使用旨在降低原子物种溶解度的催化剂的方法一致。该分析为使用金催化剂降低异质结陡峭程度开辟了新途径，但该模型可以自然地扩展到其他催化剂和半导体。
