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Home > Thèses et HDR > PhD in 2023

03/03/2023 - Atse Julien Eric N DOHI

by Arnaud Lelevé, Laurent Krähenbühl - published on , updated on


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Atse Julien Eric N DOHI defends his PhD on March 3rd, 2023 at 10:00AM.
Place : INSA de Lyon, bâtiment Ferrier, Amphi AE1

Multiphysics Characterization of GaN Materials and devices for Power Applications

Jury :
- Bertrand BOUDART, Professeur au GREYC, Université de Caen
- Martin KUBALL , Professeur à l’ Université de Bristol (UK)

- Sandrine JUILLAGUET, Maître de Conférence HDR au L2C, Université de Montpellier II
- Nathalie MALBERT, Professeure des Universités, Université de Bordeaux

- Camille SONNEVILLE, Maître de Conférence, INSA LYON
- Dominique PLANSON, Professeur des Universités, INSA LYON

Abstract :
Silicon power electronics has shown its limits due to its incapacity to sustain high voltage, high temperature and high frequency applications. Therefore, the need to resort to materials with larger band gap and solve silicon (Si) technological issues for high voltage operations has been getting more and more intense. Wide band gap materials such as Silicon Carbide (SiC), Gallium Nitride (GaN), and Diamond are very promising for power electronics because of their interesting physical properties such like high carrier mobility, high critical electric field and good thermal conductivity than Si that enable them to perform at high voltage and temperature domains. Semiconductors manufacturing companies indeed, consider them as potentials
power or current converters, inverters and rectifers for improving home and industrial energy distribution and consumption in a better way. However, the road to get them
into a larger mass production technology is still long because recent researches have shown that their performance is pinned by some physical phenomena such as structural defects appearance, strain and stress effects, doping and dopant control and effectivess and so on. Thus, ruling out these problems by a deep understanding of the physical mechanisms behind them is a key option in optimizing their performance. In this thesis, we confronted the physical and electrical properties of GaN material and devices through multiphysics and electrical characterizations approach such as micro Raman, cathodoluminescence and classical current-voltage I (V) measurements. The objective is to get an insight into the physical performance of these power electronic materials (SiC, GaN), especially of GaN based power devices due to their higher carrier mobility compared to SiC and their growing technology maturity for mass production and distribution; and suggest if possible, ways of optimizing their operating abilities at a micro level. The coupling of these characterization methods allow us to have a deep view of the physical mechanisms that support the high voltage or temperature
operation of these GaN based materials and as well as help us to grab the discrepancy existing between physical theoretical parameters established through finite elements simulations and true experimental value.

In order to conduct this work better, the thesis has been split in seven chapters starting from bibliography aspects of GaN materials and devices to the results that we have obtained during the project. The chapter 1 presents a general overview of GaN material, its physical properties, introduces the state of the art on GaN power devices and finally exposes the interest of this thesis for GaN vertical devices. The chapter 2 gives details about the physical and non-destructive characterization tools such as Micro Raman spectroscopy and Cathodo-Luminescence used in this project. In chapter 3, the generality of the electrical characterization method by current–voltage (I-V) measurements, especially on GaN Schottky devices is shown.
In chapter 4, the first result of our work is presented. This chapter is a study of GaN substrates using micro-Raman spectroscopy for the purpose of vertical device technology. The objective was to investigate the residual stress in these n-doped GaN substrates by investigating some Raman modes. In Chapter 5, micro Raman characterizations ofhomoepitaxial n-doped GaN layers with different Si concentration have been performed. The objective is to probe the doping concentration level and its influence on the GaN material and devices crystalline quality. In chapter 6, physical characterizations using a correlation approach between micro-Raman and Cathodo-Luminescence spectroscopy has been performed on some vertical GaN Schottky diodes. Finally, in chapter 7, we present the electrical properties of the same diodes used in chapter 6 and we establish a correlative study between their physical properties and their electrical behaviors.

Keywords :
GaN, Micro Raman spectroscopy, Cathodoluminescence, GaN devices, I-V measurements.

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