Multilayer Growth in Ternary InGaAs Nanowires Revealed by In Situ Transmission Electron Microscopy

<i>In Situ</i> transmission electron microscopy (TEM) has proven itself to be an important and powerful tool for unraveling many different aspects of III-V semiconductor nanowire growth, including growth dynamics^1–3 and compositional relationships.⁴^,⁵ Recently, the <i>In Situ</i> TEM investigations have shown the possibility of having more than one biatomic layer nucleate and grow simultaneously at the growth front of binary compound nanowires growing in the vapor liquid solid (VLS) mode.⁶^,⁷ The classical view has been that liquid nanoparticle mediated growth only allows the nucleation and growth of singular layers, separated by incubation periods. The discovery of multiple nucleation events and subsequent growth of multilayers contradicts this previous assumption. The finding is important, since the possibility of multiple nucleations will change the way continuous growth is viewed, and unravels more details about the delicate energy balance at the growth front. Therefore, in order to gain a deeper understanding of the nanowire growth process, and to give new insight into axial nanowire growth, the multilayer growth mode must be further investigated.<br/><br/>In this study, the growth of Au-seeded InGaAs nanowires were investigated using environmental TEM, revealing the occurrence of multilayers in ternary nanowires <i>In Situ</i>. The experiments were carried out in a Hitachi HF3300S environmental transmission electron microscope with an open cell configuration, integrated with a metal-organic chemical vapor deposition (MOCVD) system. The MOCVD system was used to supply the metal-organic and hydride precursors for the growth near a resistively heated, partially electron transparent micro-electro-mechanical system (MEMS) chip. Pre-deposited Au nanoparticles on the MEMS chip collected the growth material and initiated the growth of the nanowires. The growth was observed and recorded using a Gatan OneView IS camera, and compositional analysis was carried out through X-ray energy dispersive spectroscopy.<br/><br/>We show that multilayer growth is more prominent in InGaAs than for the binary cases previously shown, and that when multilayer growth occurs, the stacks of layers growing simultaneously can reach much larger sizes.⁷ The multilayer stacks are observed in conjunction with defects in the material, such as crystallographic twins and small compositional changes, but also at sharper compositional heterostructures. Importantly, material transport is observed between the simultaneously growing layers, indicating that the final composition of the segment could be affected. We have also observed multilayer growth as an intermediate step to kinking, a process where the nanowire changes growth direction, which is often unwanted. Since composition and uncontrolled kinking of the nanowire greatly affects its properties and performance, the discoveries are important for device applications. This shows why multilayer growth needs to be further explored, so that it can be controlled and accounted for in future nanowire growth.<br/><br/>References:<br/>1.Maliakkal, C. B. <i>et al.</i> Independent Control of Nucleation and Layer Growth in Nanowires. <i>ACS Nano</i> <b>14</b>, 3868–3875 (2020).<br/>2.Tornberg, M. <i>et al.</i> Kinetics of Au–Ga Droplet Mediated Decomposition of GaAs Nanowires. <i>Nano Lett.</i> <b>19</b>, 3498–3504 (2019).<br/>3.Harmand, J. C. <i>et al.</i> Atomic Step Flow on a Nanofacet. <i>Phys. Rev. Lett.</i> <b>121</b>, 166101 (2018).<br/>4.Maliakkal, C. B. <i>et al.</i> In situ analysis of catalyst composition during gold catalyzed GaAs nanowire growth. <i>Nat. Commun.</i> <b>10</b>, 4577 (2019).<br/>5.Sjökvist, R. <i>et al.</i> Compositional Correlation between the Nanoparticle and the Growing Au-Assisted InxGa1–xAs Nanowire. <i>J. Phys. Chem. Lett.</i> <b>12</b>, 7590–7595 (2021).<br/>6.Tornberg, M. <i>et al.</i> Direct Observations of Twin Formation Dynamics in Binary Semiconductors. <i>ACS Nanosci. Au</i> <b>2</b>, 49–56 (2022).<br/>7.Gamalski, A. D. <i>et al</i>. Atomic Resolution in Situ Imaging of a Double-Bilayer Multistep Growth Mode in Gallium Nitride Nanowires. <i>Nano Lett.</i> <b>16</b>, 2283–2288 (2016).