El Hajraoui Khalil, Robin Eric, Zeiner Clemens, Lugstein Alois, Kodjikian Stéphanie, Rouvière Jean-Luc, Den Hertog Martien
Université Grenoble Alpes , F-38000 Grenoble , France.
CNRS, Institut NEEL , F-38000 Grenoble , France.
Nano Lett. 2019 Dec 11;19(12):8365-8371. doi: 10.1021/acs.nanolett.9b01797. Epub 2019 Nov 6.
A promising approach of making high quality contacts on semiconductors is a silicidation (for silicon) or germanidation (for germanium) annealing process, where the metal enters the semiconductor and creates a low resistance intermetallic phase. In a nanowire, this process allows one to fabricate axial heterostructures with dimensions depending only on the control and understanding of the thermally induced solid-state reaction. In this work, we present the first observation of both germanium and copper diffusion in opposite directions during the solid-state reaction of Cu contacts on Ge nanowires using in situ Joule heating in a transmission electron microscope. The in situ observations allow us to follow the reaction in real time with nanometer spatial resolution. We follow the advancement of the reaction interface over time, which gives precious information on the kinetics of this reaction. We combine the kinetic study with ex situ characterization using model-based energy dispersive X-ray spectroscopy (EDX) indicating that both Ge and Cu diffuse at the surface of the created CuGe segment and the reaction rate is limited by Ge surface diffusion at temperatures between 360 and 600 °C. During the reaction, germanide crystals typically protrude from the reacted NW part. However, their formation can be avoided using a shell around the initial Ge NW. direct Joule heating experiments show slower reaction speeds indicating that the reaction can be initiated at lower temperatures. Moreover, they allow combining electrical measurements and heating in a single contacting scheme, rendering the Cu-Ge NW system promising for applications where very abrupt contacts and a perfectly controlled size of the semiconducting region is required. Clearly, in situ TEM is a powerful technique to better understand the reaction kinetics and mechanism of metal-semiconductor phase formation.
在半导体上制作高质量接触的一种有前景的方法是硅化（用于硅）或锗化（用于锗）退火工艺，在该工艺中金属进入半导体并形成低电阻金属间相。在纳米线中，此工艺能够制造出轴向异质结构，其尺寸仅取决于对热诱导固态反应的控制和理解。在这项工作中，我们首次利用透射电子显微镜中的原位焦耳加热，观察到在锗纳米线上的铜接触固态反应过程中锗和铜沿相反方向扩散。原位观察使我们能够以纳米空间分辨率实时跟踪反应。我们跟踪反应界面随时间的推进情况，这为该反应的动力学提供了宝贵信息。我们将动力学研究与基于模型的能量色散X射线光谱（EDX）的非原位表征相结合，结果表明锗和铜都在生成的CuGe段表面扩散，并且在360至600°C的温度范围内反应速率受锗表面扩散限制。在反应过程中，锗化物晶体通常从反应后的纳米线部分突出。然而，使用围绕初始锗纳米线的壳层可以避免其形成。直接焦耳加热实验显示反应速度较慢，这表明反应可以在较低温度下启动。此外，它们允许在单一接触方案中结合电学测量和加热，使得Cu-Ge纳米线系统在需要非常陡峭的接触和完美控制半导体区域尺寸的应用中具有前景。显然，原位透射电子显微镜是一种强大的技术，可用于更好地理解金属 - 半导体相形成的反应动力学和机理。
