Controlled growth of SiGe nanowires by addition of HCl in the gas phase

TLDR: In this article, a qualitative model based on the experimental results is proposed to explain the role of HCl during the growth of Si, Ge, and alloyed nanowires.

Abstract: Growth of Si, Ge, and, thus, SiGe nanowires (NWs) by catalyzed chemical vapor deposition proceeds at different process conditions, preventing easy realization of axial multijunctions interesting for device realization. In this paper, we propose a common process to obtain both Si, Ge, and alloyed NWs simply by adding HCl in the gas phase. It is demonstrated that addition of HCl during the growth improves the structural quality of the SiGe NWs, avoids the tapering of NWs by decreasing the uncatalyzed growth, increases the Ge fraction of the SiGe alloy NWs, and decreases the growth rate. A qualitative model based on the experimental results is proposed to explain the role of HCl during the growth. This model can be more generally applied to explain the tendency observed in the literature concerning the growth of SiGe alloyed NWs without HCl. It is based on a competition between adsorption, decomposition, and incorporation of Si and Ge in the catalyst. This competition is mainly regulated by the gas phase composition and by the reaction between the reactive species and the catalyst surface.