Investigation of the cross-sectional morphology of epitaxial Si nanowires grown by chemical vapor deposition for the fabrication of vertical devices

Abstract

The interfacial structure of Si nanowire transistors is decisively important to their electronic properties. Smooth sidewall surface of Si nanowires is therefore a prerequisite for the fabrication of vertical transistors. In this study, the axial cross-sectional morphology of epitaxial Si nanowires, which are grown vertically on Si[111] substrates by chemical vapor deposition via the vapour-liquid-solid mechanism, are analyzed by transmission electron microscopy to understand their surface morphology. It is noted that the cross-sections do not exhibit sharp facets. The roughness of the sidewall surface is attributed to precipitation of Si from AuSi liquid droplets. The cross-sectional shape of the Si nanowires is truncated-triangular, but not exactly symmetric. A larger distortion of the cross-sectional shape appears in tilted nanowires. It is also demonstrated that after removing the surface Au, post-growth oxidation of Si nanowires is helpful to rebuild smooth sidewall surface.