Growth Dynamics and Morphology of GaP Nanowires investigated via Transmission Electron Microscopy

In this work, the growth of GaP nanowires is demonstrated. Self-catalyzed nanowires were grown in a conventional MOVPE reactor by predeposition of Ga droplets by group III precursor preflow. Several growth series demonstrate the control over the morphology of the nanowires. Nanowire diameter can be...

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Bibliographic Details
Main Author: Krug, David Peter
Contributors: Volz, Kerstin (Prof. Dr.) (Thesis advisor)
Format: Doctoral Thesis
Language:English
Published: Philipps-Universität Marburg 2023
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Summary:In this work, the growth of GaP nanowires is demonstrated. Self-catalyzed nanowires were grown in a conventional MOVPE reactor by predeposition of Ga droplets by group III precursor preflow. Several growth series demonstrate the control over the morphology of the nanowires. Nanowire diameter can be controlled by temperature as well as TMGa preflow time, while the nanowire length is controlled by growth time. The conicity of the nanowires can be changed by a variation of the applied V/III precursor ratio. These achievements form a starting point for further growth experiments such as the growth of core/shell structures with GaP nanowires as cores. After finding the optimal growth parameters, also a transfer of the self-catalyzed growth to the in-situ setup is possible. The nanowires, presented in this work, which were grown in the in-situ setup, are grown with gold nanoparticles as catalysts. The grown nanowires show a linear dependence of their growth rate with the interface ratio. By this, the incorporation of the growth material in the catalyst droplet could be identified as the growth rate limiting step in VLS mechanism. Furthermore, investigations of the growth rates in dependence of the applied V/III ratio show that at a V/III ratio of 6.2±0.9, a transition from group V limited to group III limited growth takes place. This finding is in agreement to those in conventional MOVPE reactors, demonstrating the comparability of the in-situ setup with these MOVPE reactors. In a last step of investigation, the grown nanowires were investigated post-growth. Especially, the formation mechanism of the dominant kinks could be identified. Orientation mapping via SPED showed that a twin boundary of first order can initiate 70.5° and 109.5° kinks of the nanowires. The also frequent 123.7° kinks can be explained by second order twins. The relative occurrence of this kinks can presumably be explained a change in the elemental termination of the growth surface at 109.5° kinks. The twinning of the second-order by two subsequent 109.5° kinks could prevent this change in termination and thus explain the suppression of the 109.5° kink angles as well as the high occurrence of 123.7° kinks. It is expected that the formation of nanowire kinks is a thermodynamic effect and could be suppressed by the change in growth parameters, like the growth temperature.
DOI:10.17192/z2024.0079