Optimization of the electroluminescence efficiency of 3D visible MicroLED for displays applications

Abstract :
This thesis deals with the electrical modelling of GaN axial nanowires for displays applications. These electrical modelling are mainly focused on the study of carrier's injection pathways in the active region of a LED in order to optimize them. The display market is first presented to establish the interest for micro-LEDs compared to its competitors, before studying the properties of GaN LEDs, as well as the use of nanowires to obtain efficient structures. A study dedicated to the different physical mechanisms occurring in an LED is then presented, in order to evaluate the pertinence of the latter and realize simple simulations that correlate with experimental observations. Different models have been used on a simple planar structure, and it has been shown that the computation of radiative recombination must be carried out with care, depending on the selected models. Then, based on the previously studied structure, structural variations have been explored in order to study how modifying injection mechanisms would impact the performances of the component. Using pathways through low potential barriers has been found to be always preferable, as long as it does not degrade the quality of the quantum wells. Furthermore, it is shown that the modelling of multi-quantum wells requires the use of multiple planes of polarizations, to obtain values of threshold voltage comparable to the one observed experimentally. The simulations have finally been oriented towards bidimensional structures based on nanowires, grown at Aledia, in order to study how geometric modifications could influence their injection efficiency. A peculiar phenomenon involving multiple maxima of efficiency has been explained using these simulations as the contribution from polar and semi-polar quantum wells. Finally, a study on the optimization of a multi-quantum well structure geometry has allowed to determine technological guidelines for the design of efficient micro-LED based nanowires.

Jury members :

• Jean-Yves DUBOZ, RESEARCH DIRECTOR, CNRS : Supervisor
• Quentin RAFHAY, ASSISTANT PROFESSOR,Université Grenoble Alpes : Co-supervisor
• Mehdi DAANOUNE, ENGINEER , Aledia : Co-supervisor
• Nicolas GRANDJEAN, PROFESSOR, EPFL : Reviewer
• Fabien MANDORLO, ASSISTANT PROFESSOR, INSA Lyon : Reviewer
• Maria TCHERNYCHEVA, RESEARCH DIRECTOR, CNRS C2N :Examiner
• Julien PERNOT, PROFESSOR, Université Grenoble Alpes :Examiner