Solid-phase diffusion mechanism for GaAs nanowire growth

Persson, Ann; Larsson, Magnus; Stenström, Stig; Ohlsson, Björn; Samuelson, Lars; Wallenberg, L. Reine

doi:10.1038/nmat1220

Cited by 653 publications

(652 citation statements)

References 18 publications

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“…This effect, already reported for GaAs NWs grown by chemical beam epitaxy [3], is interpreted as a partial consumption of the Ga dissolved in the gold particle to form the terminal section of the NW.…”

supporting

confidence: 57%

Why Does Wurtzite Form in Nanowires of III-V Zinc Blende Semiconductors?

2007

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We develop a nucleation-based model to explain the formation of the wurtzite (WZ) phase during the vapor-liquid-solid growth of free-standing nanowires of zinc-blende (ZB) semiconductors. Nucleation occurs preferentially at the edge of the solid/liquid interface, which entails major differences between ZB and WZ nuclei. Depending on the pertinent interface energies, WZ nucleation is favored at high liquid supersaturation. This explains our systematic observation of ZB during early growth.PACS numbers: 68.65. La,64.60.Qb,81.05.Ea,81.15.Kk,64.70.Nd Free-standing wires with diameters ranging from hundreds down to a few nanometers are nowadays commonly fabricated from a large range of semiconductor materials [1,2,3,4,5]. These nanowires (NWs) have remarkable physical properties and many potential applications. The present work deals with the epitaxial growth of NWs of III-V semiconductors on a hot substrate. Metal catalyst nanoparticles deposited on the substrate before growth define the wire diameter. According to the vapor-liquidsolid (VLS) growth mechanism, the atoms are fed from the vapor phase to the solid wire through this particle (or droplet), which remains liquid during growth [6].We consider III-V compounds which, under bulk form, adopt the cubic zinc-blende (ZB) crystal structure [7] (although some non-ZB high-pressure phases [8] may be metastable at atmospheric pressure [9]), leaving aside nitrogen-based NWs. We discuss the usual case of NWs grown on a [111]B (As-terminated) face of the ZB substrate. Probably the most surprising feature of these NWs is that, in contrast to their bulk counterparts, they often adopt the hexagonal wurtzite (WZ) structure. This was observed for most ZB III-V materials and growth techniques [1,3,4,10,11]. However, although often dominantly of WZ structure, the NWs usually contain stacking faults (SFs) and sequences of ZB structure. The coexistence of two phases is clearly a problem for basic studies as well as applications, so that phase purity control is one of the main challenges of III-V NW fabrication.The surprising prevalence of the WZ structure in III-V NWs has not been explained satisfactorily so far. Here, based on new experimental observations, we propose an explanation of the occurrence of the WZ structure and develop a model predicting quantitatively in which growth conditions it should form. We consider the specific case of gold-catalyzed GaAs NWs grown by molecular beam epitaxy (MBE) on a GaAs substrate but we expect our model and our conclusions to remain valid for any ZB III-V compound and any growth method.Let us start with briefly reviewing previously proposed explanations. Calculations give the difference δw in cohesive energy between ZB and WZ bulk GaAs as about 24 meV per III-V pair at zero pressure [7]. It has been argued that this favoring of the ZB form might be offset in NWs of small diameter by the large relative contribution to the total energy of either the lateral facets [12] or the vertical edges separating the latter [13] (provided the specifi...

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confidence: 57%

Why Does Wurtzite Form in Nanowires of III-V Zinc Blende Semiconductors?

2007

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“…These effects ͑precipitation of Zn out of cooling NR and consequent tapering of the ends of NR͒ have previously been reported for the behavior of Ga in the growth of GaAs NR in As-rich and As-deficient environments and our observations support the mechanism proposed in that report. 39 The absence of Si signals in the EDX data of Au tips on top of VLS NR strongly implies that alloying with Si/ SiO 2 is not required for VLS NR growth. If Si were incorporated at high temperature growth and precipitated out ͑and oxidized͒ as the system cooled ͑as predicted by the Au-Si phase diagram 37 ͒, one would expect to observe a Si/ SiO 2 shell or similar Si-composed deposit close to the NR Au tip.…”

Section: -950°c Growth Temperaturesmentioning

confidence: 99%

Growth of ZnO nanostructures on Au-coated Si: Influence of growth temperature on growth mechanism and morphology

Kumar

McGlynn

Biswas

et al. 2008

Journal of Applied Physics

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ZnO nanostructures were grown on Au-catalyzed Si silicon substrates using vapor phase transport at growth temperatures from 800 to 1150°C. The sample location ensured a low Zn vapor supersaturation during growth. Nanostructures grown at 800 and 850°C showed a faceted rodlike morphology with mainly one-dimensional ͑1D͒ growth along the nanorod axis. Samples grown at intermediate temperatures ͑900, 950, and 1050°C͒ in all cases showed significant three dimensional ͑3D͒ growth at the base of 1D nanostructures. At higher growth temperatures ͑1100 and 1150°C͒ 3D growth tended to dominate resulting in the formation of a porous, nanostructured morphology. In all cases growth was seen only on the Au-coated region. Our results show that the majority of the nanostructures grow via a vapor-solid mechanism at low growth temperatures with no evidence of Au nanoparticles at their tip, in sharp contrast to the morphology expected for the vapor-liquid-solid ͑VLS͒ process often reported as the growth mechanism on Au-catalyzed Si. We see VLS growth only at 900 and 950°C. Transmission electron microscopy data indicate that the nanorods are single crystalline without gross structural defects. Luminescence data reveal strong ultraviolet emission in all samples and weak defect emission in the visible region. We discuss the growth mechanisms with reference to various models in the literature and suggest reasons for VLS growth only in a narrow temperature range. We also discuss the potential effects of the Zn oxidation reaction on the growth morphologies, aspects largely ignored in the general literature on this subject.

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“…The choice of this combination is also because only group III elements are known to diffuse through the catalysts ͑As does not alloy with the Au catalysts͒. 12 The details of heterointerface with a change in the group-III element should provide insight into NW growth and the role of the nanosized catalyst. Although the axial GaAs/InAs NW heterostructures have been reported earlier, 13,14 no detailed investigation of the GaAs/InAs heterointerfaces were given, though this information is important.…”

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confidence: 99%

“…It should be noted that, after growth termination and during cooling, Ga may be released from the catalyst particles and reacts with ambient As vapor species to form GaAs. 12,15 In the case of InAs NWs ͑cooled under As vapor species͒, In was found inside the Au catalysts. 16 Even in the case of InGaAs NWs ͑cooled under As vapor species͒, Ga was released and only In was detected in the Au catalysts after the cooling .…”

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confidence: 99%