Nucleation and growth of metal-catalyzed silicon nanowires under plasma

Abstract

We report the results of a microscopic study of the nucleation and early growth stages of metal-catalyzed silicon nanowires in plasma-enhanced chemical vapor deposition. The nucleation of silicon nanowires is investigated as a function of different deposition conditions and metal catalysts (Sn, In and Au) using correlation of atomic force microscopy and scanning electron microscopy. This correlation method enabled us to visualize individual catalytic nanoparticles before and after the nanowire growth and identify the key parameters influencing the nanowire nucleation under plasma. The size and position of catalytic nanoparticles are found to play a significant role in the nucleation. We demonstrate that only small isolated nanoparticles in the range of 10–20 nm contribute to the nanowire growth under plasma, while larger nanoparticles are inactive because they get buried under a layer of a-Si:H before reaching supersaturation. Systematic analysis of different growth parameters reveals that the nanowire growth in plasma contradicts the vapor–liquid–solid mechanism at thermal equilibrium in many ways. The nanowire growth is much faster and proceeds even at negligible silicon solubility and bellow the eutectic temperature of the metal-silicon alloy. Based on the observations, we propose the nanowire growth under plasma to be characterized by the rapid solidification mechanism, where a crystalline silicon phase emerges from a metastable supersaturated liquid metal-silicon phase in local nonequilibrium.

Research progress of out-of-plane GeSn nanowires

“…For example, the Sn content of out-of-plane GeSn NWs obtained by growth using the Au 1-x Ag x catalytic alloy is higher than that of NWs catalyzed using pure Au in the case of similar diameters [56]. Therefore, the composition of liquid droplet is also one of the factors affecting the nucleation of NWs and the incorporation of Sn in GeSn NWs [139,140]. Since nano-systems are characterized by high surface-to-volume ratios, the surface energy contribution to the thermodynamics is prominent, making the growth rate dependent on the diameter, and the radial dependence of the chemical potential can be expressed as follows [141][142][143]:…”

Coalescence, crystallographic orientation and luminescence of ZnO nanowires grown on Si(001) by chemical vapour transport

“…The synthesis of semiconductors in the form of nanowires (NWs) instead of epitaxial films provides new degrees of freedom for the design of opto-and electronic devices as well as the possibility of combining otherwise incompatible materials [1][2][3][4][5]. Among the wide variety of semiconductors that can be grown as NWs, ZnO and GaN stand out.…”