Description du sujet de thèse

Scientific field and context:
Electronic components based on wide band gap semiconductor (SiC, GaN) are experiencing considerable growth for applications in medium-power electronics (1 kV / 10 A) such as the hybrid/electric automotive sector. Beyond this power range, the challenges for an electronic with increase power density and switching/conversion efficiency are considerable from the point of view of energy issues and the reduction of CO2 emissions, with applications in the field of power distribution (smart grid) and transport (rail) for instance. To meet these power requirements, it is necessary to turn to so-called ultra-wide gap materials (UWBG) with bandgap energies (4 eV) and breakdown fields (~ 10 MV.cm-1) such as diamond, AlGaN or Ga2O3. The latter has the unique advantage of the availability of commercial substrates with a diameter of 150 mm at a reasonable cost (3 times cheaper than SiC). A very big challenge for UWBG materials is doping. Here again, Ga2O3 is of great interest since n-doping can be easily performed over a wide range [1-3]. Unipolar power devices have been demonstrated with normal-on operation [4-6]. The missing technological building block for normally-off power devices is p-type doping for the production of bipolar devices. The study of p-type doping is the subject of a thesis started in the laboratory (Mrs. O. Heribi). For the time being, this difficulty is circumvented by the use of a heterojunction with nickel oxide (NiO type) p [7]. However, when the dimensions of the devices are extended to obtain high currents in the on state, the voltage resistance suffers greatly. This can be explained by the presence of electrically active defects under the diode and/or by the difficulty of making edge terminations. The objective of the thesis will therefore be to characterize the electrically active defects present in the Ga2O3 material as well as those induced by the technological processes used to realize the edge terminations (implantations, etching, passivation). To this end, the INL laboratory and the "Functional Materials" team have a real original expertise in electrical and electro-optical techniques for the study of electronic levels induced by traps and defects in wide-gap semiconductors.
In addition, the thesis is funded as part of a national PEPR project (Priority Research Program and Equipment) whose aim is to create a power diode (10 kV, 10A) with its packaging. To do this, the consortium brings together French experts in Ga2O3 epitaxy (GEMAC), NiO Epitaxy (CEA-IRIG), technological integration (IEMN), power simulation and characterization (Ampere) and packaging associated with chip thermal management (LGP). The defect characterizations conducted at INL will be complemented by electronic paramagnetic resonance measurements conducted at INSP.
Objectives of the thesis:
The overall objective is therefore to characterize the properties of electrically active defects in Ga2O3 epitaxy and in the power diodes made on these epitaxy.
The thesis work will therefore consist of developing techniques for characterizing defects on a material with a very large bandgap (4.8 eV). Indeed, the classic DLTS technique will be advantageously complemented here by optical or electro-optical techniques such as ODLTS (optical DLTS) and DLOS allowing the activation and observation of very deep defects thanks to the photo-ionization of free carriers. The measurement of photo-induced current transients, particularly suitable for large gaps due to the use of UV optical sources, will also be used. We will also provide classical capacitive DLTS measurements under strong reverse fields in order to probe the drift layer of power devices. These developments will be based on existing equipment (two capacitive DLTS setup currently in operation, one of which is equipped with optical sources) and a spectrometer.
These characterization methods will be used for two purposes:
1) Studies on the defects of the material and in particular homo-epitaxy will be carried out in collaboration with the GeMaC laboratory in charge of the growth of thick layers (typically 10 μm or more) of n type. Parameters modifications in order to increase the growth rate may be the cause of defects creation that will need to be identified. The control of low doping ( 1016 cm-3) will also be a challenge requiring in-depth electrical characterizations (I-V and C-V in temperature, DLTS to understand the role of traps). To carry out these characterizations, it will be necessary to realize Schottky diode. To do this, the doctoral student will rely on the design skills of the Ampère laboratory on the one hand and on the INL technological platform on the other. The levels of masks required for these studies have already been thought out and designed as part of another thesis (M. Ghangzi Lu) in co-direction with the Ampère laboratory. These masks also contain patterns for performing OBIC (Optical Beam Induced Current) measurements that allow the measurement of impact ionization coefficients (this parameter is essential for the simulation of components breakdown in strong fields).
Still considering material studies, simple pn junctions (without edge termination) will then be realized (in the laboratory or at the IEMN) on the NiO(p)/Ga2O3(n) heterojunctions. The aim will also be to characterize the defects of this heterojunction by trying to discern those that may come from the NiO layer (we will rely on the previous study of Ga2O3 alone).
2) The second objective is the study of power devices (diodes with peripheral protections) that will be carried out at the IEMN for pn diodes as part of the GOTEN project, and at INL for Schottky diodes as part of M. Lu's thesis. The realization of these devices will require the realization of MESA etching by ICP, possible implantations to make the material insulating or p-type to fabricate JTEs in the case of Schottky (N and P implantations that will be studied in the framework of Ms. Latra's thesis) and passivation layers. All these technological steps are likely to create electrically active traps that are potentially deleterious to the operation of the diode and in particular its reverse voltage performance. The defect spectroscopy studies previously set up will make possible to carry out this analysis. These studies will be coupled with measurements of electrical characteristics (I-V, C-V) carried out in low current and voltage at the INL (10 mA, 100 V, or 1 W) and under high fields or at high current at Ampere.

The study will therefore make it possible to correlate the defect spectroscopy data with possible failure of the devices observed on their electrical characteristics. The two parts will make it possible to understand the origin of these defects in order to discern those due to growth from those induced by technological processes. Finally, the signatures of the traps (activation energy, capture cross-section) can be used as incoming parameters for the modelling of the components, as well as the impact ionization coefficients.
Research program and proposed scientific approach:
The thesis will start with the DLTS study of n-type epitaxy in order to characterize the defects in this material and then with the implementation of the optical extensions (DLOS, ODLTS) necessary for the study of the UWBG material (this will be done in collaboration with Ms. Latra).
This part will be done in strong interaction with Gemac.
These techniques will then be applied to the study of pn NiO/Ga2O3 heterojunctions in interaction with Gemac and CEA-IRIG.
The work of the second year and the beginning of the third year will consist of studying power diodes (Schottky INL-Ampere and pn IEMN) with the aim of correlating defects with electrical characteristics (ideality factor for example) and to segregate the problems related to technology and those related to the material.

Environment:
As mentioned in the introduction, this thesis is part of the PEPR Goten research project bringing together French experts in the wide band gap semiconductor field with skill extending from material to packaging. At the local level, the PhD student will benefit from a strong synergy between the Ampère and INL laboratories, giving rise to a very good dynamic on the development of the Ga2O3 technology in Lyon. The obtention fundings with the PEPR project, a thesis in 2023 at the EEA doctoral school (Mr. Lu) and another thesis at the EDML doctoral school in 2024 (Mrs. Latra) testifies to this dynamic and the confidence placed in the lead laboratories. Thus, this thesis work will be carried out within a small team (3 PHDs and their supervisors + a post-doctoral fellow at Ampère) promoting effective work through mutual aid and synergy with, as presented in the description of the work, very distinct fields of research for each thesis.

Contexte de travail

The Institut des Nanotechnologies de Lyon (INL) aims to develop multidisciplinary technological research in the field of micro and nanotechnologies and their applications. The research carried out extends from materials to systems. The laboratory is based on the NanoLyon technological platform in Lyon.
Application areas cover broad economic sectors: semiconductor industry, information technology, life and health technologies, energy and the environment.
The laboratory is multi-site with locations on the Ecully and Lyon-Tech La Doua campuses. It comprises around 200 people, including 121 permanent staff. INL is a major player in the Research and Teaching Cluster.
This position is located in an innovative environment, at the forefront of future technologies, in strategic application sectors.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

No constraints or special risks.