Thesis presented April 05, 2017

Abstract:
Group-III-nitride nanostructures are considered as promising candidates aiming at the realization of various innovative devices, including fields from electronics, photonics, to biochemistry and energy. Since recent years, a growing interest of InGaN-based nano-LEDs has been raised in the field of lighting and display. This PhD work focuses on the growth by plasma-assisted molecular beam epitaxy and on the characterization of nanowire-based InGaN/GaN heterostructures.
Firstly, a kinetic growth model of III-nitride nanowires has been established, aiming at an in-depth analysis and a better control of atomically kinetic processes involved in MBE growth. This modeling work constructs the theoretical basis and guides the experimental interpretation in this thesis.
Then, the morphological, inner-structural, compositional and optical properties of axial GaN/InGaN/GaN nanowire heterostructures have been investigated at nano-scale by a combination of electron microscopy (SEM/STEM/TEM), photoluminescence (PL), nano-cathodoluminescence (nano-CL), energy-dispersive X-ray spectroscopy (EDX). On the basis of experimental results, we have achieved a statistical description of morphological landscape for all InGaN/GaN NWs under different thermodynamic and atomic fluxes conditions. Meanwhile, the correlation between the morphological & compositional features and the electronic & optical properties of InGaN/GaN NWs has been established.
Furthermore, various types of NW-based InGaN superstructures have been grown and investigated. It is found that both axial growth rate and real In composition will decrease in the case of Indium excess, due to In surfactant effect and a reduced effective nitrogen flux. Meanwhile, a dramatic widening of InGaN sections has been observed under N-rich condition, suggesting the metal-rich condition is not necessary for the InGaN enlargement. Accordingly, we propose the driving mechanism of InGaN growth, for which the axial growth is a flux-determined kinetic process and the lateral widening is mainly strain-induced.
Finally, we have investigated the influence of post-growth annealing process for the luminescence efficiency and proposed our growth recipes of LED plates, aiming at approaching the fabrication of MBE-grown LED plates.

Keywords:
Molecular beam epitaxy, Nanowires, Growth kinetics, InGaN/GaN heterostructures, NW-based InGaN superstructures, Compositional fluctuation