Self-branching in GaN Nanowires Induced by a Novel Vapor-Liquid-Solid Mechanism

Abstract

Nanowires have great potential as building blocks for nanoscale electrical and optoelectronic devices. The difficulty in achieving functional and hierarchical nanowire structures poses an obstacle to realization of practical applications. While post-growth techniques such as fluidic alignment might be one solution, selfassembled structures during growth such as branches are promising for functional nanowire junction formation. In this study, we report vapor-liquid-solid (VLS) self-branching of GaN nanowires during AuPdcatalyzed chemical vapor deposition (CVD). This is distinct from branches grown by sequential catalyst seeding or vapor-solid (VS) mode. We present evidence for a VLS growth mechanism of GaN nanowires different from the well-established VLS growth of elemental wires. Here, Ga solubility in AuPd catalyst is limitless as suggested by a hypothetical pseudo-binary phase diagram, and the direct reaction between NH3 vapor and Ga in the liquid catalyst induce the nucleation and growth. The self-branching can be explained in the context of the proposed VLS scheme and migration of Ga-enriched AuPd liquid on Ga-stabilized polar surface of mother nanowires. This work is supported by DOE Grant No. DE-FG02-98ER45701. KeywordsGallium alloys, Dissolution, Electric wire, Gallium nitride, Liquids, Nanowires, Semiconducting gallium, Vapors, AuPd alloy, GaN nanowires, Growth modes, Growth morphology, Nucleation and growth, Polar surfaces, Spontaneous reactions, Vapor-liquid-solid mechanism, VLS growth ABSTRACTInvestigations of the growth morphology of AuPd-catalyzed GaN nanowires lead us to propose a vapor-liquid-solid (VLS) mechanism distinct from the well-established VLS growth of elemental wires. Here, nucleation and growth of GaN nanowires proceeds by direct spontaneous reaction between NH 3 vapor and Ga dissolved in liquid AuPd alloy, rather than by solubilitylimited supersaturation. A frequently observed self-branching growth mode can be explained by the proposed VLS scheme and the migration of Ga-enriched AuPd liquid on Ga-stabilized polar surfaces of mother nanowires. INTRODUCTIONGaN nanowires (NWs) are of interest for nanoscale optoelectronic device applications [1][2][3][4]. Synthesis can be achieved by several methods involving vapor-liquid-solid (VLS) growth, such as thermal chemical vapor deposition (CVD) [5][6][7], hydride vapor phase epitaxy (HVPE) [8], molecular beam epitaxy (MBE) [9], and metalorganic CVD (MOCVD) [10]. The low N solubility in transition metals implies that nucleation of GaN from supersaturated catalyst droplets is unlikely, in contrast to elemental structures such as Si whiskers and NWs [11]. Here we study GaN NWs grown by thermal CVD using Ga 2 O 3 , NH 3 and AuPd catalyst. The observed morphologies suggest a VLS mechanism distinct from the nucleation and growth of elemental nanostructures from supersaturated liquid. We consider a hypothetical pseudo-binary phase diagram and thermodynamics of GaN formation reaction to propose that NW nucleation and growth occur via direct ...

One‐Step SnO2 Nanotree Growth

“…However,t his would require an exceptional mobility of Au on SnO 2 at this temperature;2 )Snp recursor atomss pontaneously form droplets on the SnO 2 trunk andb ranchesg row self-catalysed following the VLS mechanism. This also explains the observation in Figure 4c and the formation of leaves grown from smaller droplets on the branches;3 )the main catalyst particle at the tip gives off smaller particles if the size exceeds ac ertain threshold, [10] as depicted in Figure 4c.T hese particles can even migrate several micrometers along the trunk. [11] Duringt he first few micrometers of growth the size does not exceed the threshold yet.…”

Growth and Characteristics of Zinc-Blende and Wurtzite GaN Junctioned Branch Nanostructures

“…The other route may also expect a direct consequence of the Ga-stabilized polar surface and formation of liquid phase metal catalyst. If the Ga source incorporated into the Au catalyst faster than Ga is consumed by the growing GaN NRs, the tip particle can become enriched with Ga and grow in diameter, which provides the opportunity for the Ga-rich liquid to leave the tip particle, migrate along the surface of the growing GaN NRs, and ultimately nucleate branches . Finally, the branch c-GaN NWs started to grow laterally, and cubic phase embedded in h-GaN nanowires transitioned to the hexagonal phase.…”