Exploring the Dynamics of the III-Sb Nanowires During In Situ Growth

Group III-Sb semiconductor nanowires (GaSb, InSb, AlSb and their combinations) are an important material system for potential uses in applications such as quantum electronics, optoelectronics and sensing. This is due to their excellent electrical properties, including high carrier mobility and narrow band gap.¹ Among the III-Sb materials perhaps the most notable examples are InSb and GaSb nanowires which display the highest electron and hole mobilities among III-V nanowires, respectively.²<br/>Despite the superior properties of this material system little research has been conducted into it when compared to other group III-V materials, such as group III-As. To a large extent this is caused by the complex growth conditions of antimonides, as elemental antimony exhibits low vapour pressure and surfactant effect.³ The investigation of this material system is further complicated by the difficulty of growing III-Sb nanowires directly from single crystal substrates often resulting in the need to use III-As/III-Sb heterostructures.^1,4 In these heterostructured nanowires several dynamic effects can take place when switching from the III-As to the III-Sb segment such as unwanted radial expansion, change in crystal structure and facet change. Therefore, exploring the III-Sb growth parameter space has become unrealistic using conventional growth methods like metal organic chemical vapour deposition (MOCVD) which notoriously does not allow examination of the growth dynamics.<br/>In this work, we have investigated the III-Sb nanowire growth process by growing these nanowires in-situ using an open cell Hitachi HF-3300S environmental transmission electron microscope combined with an MOCVD system.⁵ To facilitate nanowire growth, metal-organics and hydrides were used as precursors and introduced near a SiN_x micro-electro-mechanical system (MEMS) heating chip covered with pre-deposited Au nanoparticles. To analyse nanowires during growth we employed X-Ray Electron Dispersive Spectroscopy (XEDS) measurements in combination with atomically resolved high-resolution transmission electron microscopy (HRTEM) imaging and videos.<br/>We focus on the III-As/III-Sb heterostructure formation; wherein we have investigated droplet composition during growth, changes in nanowire morphology, and the connection between droplet composition and growth dynamics. Special attention is directed towards the GaAs/GaSb heterostructures where we have demonstrated that radial expansion of the GaSb segment can be minimized by fine-tuning of TMGa flow. Additionally we demonstrate that both excess TMGa and TMSb supply in the vapour phase can lead to kinking of the nanowires.<br/>Results of this study have given insight into the connection between droplet composition and nanowire diameter during III-As/III-Sb heterostructure formation. This knowledge could ultimately be used in fabricating smaller diameter nanowire heterostructures ex-situ, important for device applications.<br/><br/>References:<br/>(1) Mattias Borg, B.; Wernersson, L.-E. Synthesis and Properties of Antimonide Nanowires. <i>Nanotechnology</i> <b>2013</b>, <i>24</i> (20), 202001. https://doi.org/10.1088/0957-4484/24/20/202001.<br/>(2) Ghalamestani, S. G.; Ek, M.; Dick, K. A. Realization of Single and Double Axial InSb – GaSb Heterostructure Nanowires <i>Phys. Satus Solidi</i>. <b>2014</b>, <i>273</i> (3), 269–273. https://doi.org/10.1002/pssr.201308331.<br/>(3) Ghalamestani, S. G.; Lehmann, S.; Dick, K. A. Can Antimonide-Based Nanowires Form Wurtzite Crystal Structure? <i>Nanoscale. </i><b>2016</b>, 2778–2786. https://doi.org/10.1039/c5nr07362f.<br/>(4) Yip, S.; Shen, L.; Ho, J. C. Recent Advances in III-Sb Nanowires: From Synthesis to Applications. <i>Nanotechnology</i> <b>2019</b>, <i>30</i> (20). https://doi.org/10.1088/1361-6528/aafcce.<br/>(5) Tornberg, M.; Maliakkal, C. B.; Jacobsson, D.; Wallenberg, R.; Dick, K. A. Enabling In Situ Studies of Metal-Organic Chemical Vapor Deposition in a Transmission Electron Microscope . <i>Microsc. Microanal.</i> <b>2022</b>, 1–9. https://doi.org/10.1017/s1431927622000769.