PhD defense of Alexandre DIEULESAINT 20.12.2023

« Study of hydrogen-related defects in ZnO nanowires grown by chemical bath deposition »

Mots-clés :

ZnO Nanowires Defects Hydrogen

Abstract

This thesis investigates the complex field of zinc oxide (ZnO) nanostructures, studying their synthesis, surface treatments and the influence of various parameters on their structural properties and defects. Beginning with a comprehensive exploration of ZnO nanowires fabricated by chemical bath deposition, the study describes the fundamental principles of semiconductors (Chapter 1). In particular, it meticulously reviews the structural and electrical properties of ZnO, revealing the impact of hydrogen- and nitrogen-related defects and engineering techniques to mitigate these defects. The discussion extends to the polarity aspects of the nanowires, paving the way for an understanding of their versatile behaviour in different environments.

Following on from this, this thesis examines various surface treatment methodologies (Chapter 2). Plasma processes and UV-ozone treatments are examined in depth, uncovering their nuanced effects on the morphology and defects of ZnO nanowires. Through meticulous experimentation and analysis, the study correlates the results back to the complex mechanisms of the reactions induced by these treatments, shedding light on the intricate processes at the atomic and molecular scales.

Chapters 3, 4 and 5 delve deeper into the nuances of plasma treatments, exploring the impact of oxygen ion energy, treatment duration and argon fraction in an oxygen plasma. These chapters detail the alterations in nanowire morphology and defects induced by varying these parameters, giving a deep insight into the underlying mechanisms and reactions involved.

An important part of the research focuses on the incorporation of dopants (Chapter 6). Doped and undoped ZnO nanowires are grown and meticulously characterised. The study focuses on the incorporation mechanisms of dopants such as Cu, Al, Ga and Sb, after ultraviolet ozone treatment. Using advanced spectroscopic techniques, it dissects the radiative recombination processes and the phonon and optical modes, correlating the structural modifications with the optoelectronic properties of the doped ZnO nanowires.
 

In addition, this thesis explores the impact of the polarity of a ZnO single crystal as a substrate, examining its influence on morphology, impurity and dopants incorporation in chemically doped layers (Chapter 7). Through rigorous optimisation and analysis, the study provides insight into surface modifications and their implications for layer growth processes.

In conclusion, this research provides a comprehensive understanding of ZnO nanostructures and their behaviour under various conditions. The results not only deepen fundamental knowledge of semiconductor physics, but also provide valuable insights for practical applications of ZnO nanostructures in various fields, including optoelectronics, sensors and catalysis.

Membres du jury/ Jury members :