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Novel solutions for piezogeneration enhancement in GaN nanowires

Abstract : In the last decade, GaN nanowires (NWs) have emerged as promising candidates in the field of small-scale energy harvesting. Their superior mechanical and piezoelectric properties confers to them the ability to effectively convert the ambient vibrational and mechanical energies into electrical energy, and thus develop a new generation of ultra-compact, high-efficient and self-sustainable piezoelectric generators to assist or power microelectronic devices. Despite the demonstration of first promising NW-based piezo-generators, it is today indispensable to further increase the piezo-conversion capacity of these new harvesters. The exploration of novel solutions to enhance their performances is the research axis of this thesis. Here, plasma-assisted molecular beam epitaxy (PA-MBE) is employed to grow intrinsically p-doped GaN NWs with high crystalline quality. Thanks to a nano-characterization tool based on atomic force microscope equipped with the Resiscope electric module specifically adapted for piezoelectric conversion measurements, the piezoelectric response of NWs is investigated as a function of the explored solutions. The piezo-generation efficiency of the NWs is strongly affected by the external circuit. For the first time in the nanoscale regime we experimentally demonstrate its influence on the piezo-generation efficiency of the NWs. The limitations of the formerly established protocol to judge the piezo-generation capacity of 1D-nanostructures are addressed and solutions are proposed. The piezo-generation efficiency of the NWs is also deeply affected by the surface charges, which are strongly pronounced in sub-100 nm wide GaN NWs. We demonstrate that these surface charges can be advantageous for piezoelectric applications as they offer the possibility to tune the free charge carrier concentration as a function of NW diameter. Thus, we establish experimentally that in the presence of surface charges, the electromechanical coupling efficiency of GaN NWs increases up to 43.4 % for diameters in the range of 45-60 nm. The piezoelectric measurements on GaN and GaN/Al₂O₃ core-shell NWs are also performed. The reduction of surface charge density by the Al₂O₃ shell results in a degradation of the piezoelectric response of the NWs. These results confirm the importance of the surface charges for improving the piezo-response of GaN NWs. Finally, by taking advantage of these solutions, output voltages reaching up to 520 mV per NW have been measured, stating a new-state-of-the-art, in the commonly used protocol, for 1D piezoelectric nanostructures.
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https://tel.archives-ouvertes.fr/tel-03865436
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Submitted on : Tuesday, November 22, 2022 - 12:01:09 PM
Last modification on : Thursday, November 24, 2022 - 3:34:14 AM

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  • HAL Id : tel-03865436, version 1

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Tanbir Kaur Sodhi. Novel solutions for piezogeneration enhancement in GaN nanowires. Micro and nanotechnologies/Microelectronics. Université Paris-Saclay, 2022. English. ⟨NNT : 2022UPAST116⟩. ⟨tel-03865436⟩

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