Development of red and RGB µLEDs for microdisplays and high-speed communication
Background: MicroLEDs (µLEDs) are a promising technology for the development of high-brightness mini-displays (such as augmented reality glasses or smartwatches). Measuring less than 20 µm in size, these µLEDs are produced by etching a planar structure on sapphire that incorporates InxGa1-xN quantum wells. The emitted wavelength is directly tuned by the indium content x of the quantum wells (x ˜ 15% for blue, 25% for green, 35–40% for red). While nitride semiconductors offer excellent performance in the blue spectrum, efficiency drops sharply as the size of the µLEDs decreases. To overcome this issue, an innovative approach involves microwire technology with a core-shell geometry. This architecture preserves emission efficiency regardless of size and enables data transmission at GHz speeds (technology developed by the Grenoble-based startup Aledia). Despite their strong potential, core-shell microwire LEDs still face a major scientific challenge: achieving red emission. Indium incorporation remains limited to 25%, a threshold insufficient to reach red. This technological bottleneck is currently hindering the emergence of RGB trichromatic µLEDs. Our team has achieved pioneering results in this field, where we created the first InGaN core-shell quantum well at 15% for blue emission and 25% for green emission. Despite these advances, the challenge of achieving red emission remains.
Objectives: A new idea has emerged to go beyond 25% of In-content for core-shell microwire technology and thus aim for the first demonstration of red emission, which led to a patent application in 2025. Preliminary results have proven very promising results, and we wish to continue this work through a thesis with the three main objectives:
- Demonstrate red emission by varying the geometric parameters of the microwires (diameter, etc.)
- Produce red µLEDs
- Produce trichromatic RGB µLEDs in a single growth run
Collaborations: This project relies on close collaboration with the LTM (Laboratory of Microelectronics Technology) for the fabrication of GaN microwire arrays via etching process. Epitaxial studies of core/shell LEDs will be conducted at CEA’s PHELIQS facility using the MOCVD epitaxial setup, incorporating structural and optical analyses. The final step aims to fabricate microwire-based µLED devices using the expertise developed at the Néel Institute via the NanoFab cleanroom.
Why join this project? To gain expertise in epitaxy, semiconductor physics, and optoelectronics. To work in a dynamic and collaborative environment closely linked to the industrial sector. To contribute to the development of next-generation µLEDs for micro-displays and GHz communications.
PhD Funding: This thesis project is funded by the UGA’s Labex “µelectronics.”
Characterisation of the physico-chemical properties of solid residues from biomass hydrothermal carbonisation
Hydrothermal carbonisation (HTC) is a thermochemical conversion process performed in pressurized water (2-6 MPa) between 180 and 260°C. The main product is a carbonaceous solid residue (hydrochar). Various applications are foreseen for hydrochar: combustion, gasification, adsorption, catalysis, soils amendment, hard carbon for Na-ion batteries, …, each of them requiring specific properties.
The objective of the thesis is to characterise and better understand the origin of several physico-chemical properties of biomass hydrochars. A special attention will be paid to hydrophobicity and drying capacity, to physical and textural characteristics of the particles (porosity, granulometry, specific surface), as well as to chemical characteristics (composition). The influence of biomass type and HTC conditions on these properties will be investigated.
The approach will consist in: experimentations in batch reactors on pre-selected biomass resources, together with use of different characterisation techniques for hydrochars; analysis of results aiming at determining links between the characteristics, elucidating the links between the resource and its hydrochar properties as a function of operational conditions.
Dual Active Bridge Topology Based on SiC Synthetic Switches for Ultra-Fast Active Stabilization of a Low-Inertia Converter-Dominated DC Grid.
With the massive deployment of direct current (DC) technologies on the grid, particularly photovoltaics and grid-connected battery energy storage systems (BESS), a growing share of electrical energy now flows through static power converters. Unlike classical grids dominated by rotating machines, which benefit from high natural inertia, power-electronics-dominated networks exhibit very limited inertia and may therefore experience highly dynamic voltage spikes, voltage drops, or even complete collapse. Some research focuses on synthetic inertia, emulated through specific control strategies implemented in static converters, but these approaches depend on equipment manufacturers and do not rely on established standardization. Another approach consists in designing dedicated equipment specifically intended for the active stabilization of low-inertia power systems, which is the direction explored in this PhD project.
A particularly demanding case concerns MVDC grids, which by construction rely entirely on static power converters, therefore exhibiting extremely low natural inertia, and requiring the use of converters based on specific technologies. Within the framework of this PhD, we propose the study and proof of concept of a converter connected to an MVDC electrical network operating between 6 and 12 kV, capable of injecting or absorbing very high levels of power in a transient manner, on the order of ten megawatts for durations ranging from 10 µs to 100 ms. The system will rely on an isolated Dual Active Bridge (DAB) topology, with a medium voltage capacitive DC bus at its primary.
This power electronics topic presents several technological bottlenecks. Synthetic switches (series-connected SiC devices, as investigated in a previous PhD in the laboratory) will have to be implemented in a real DAB converter. A highly isolated power supply for the gate drivers of these synthetic switches will need to be designed. The medium-frequency DAB transformer must be designed to transfer very high transient power while minimizing volume. Particular attention will therefore be paid to transient-oriented design, with the objective of identifying the key parameters that maximize, within a complex structure, the ratio between the converter rated power and its peak power.
Potential extensions toward other pulsed-power applications that could benefit from such a converter will be explored, taking into account their specific constraints.
Integrated waste treatment: design and optimisation of a multi-waste treatment scheme for a multi-purpose energy production
At the city scale, multiple waste streams such as household waste, compost, sewage sludge, yard waste, non-recyclable plastics, used oils, metals, glass, and others. All of these feedstocks exhibit variable seasonality and carbon content. Nowadays, the aforementioned streams are managed through recycling, and in some cases incineration or landfilling. Alternative treatment technologies, such as gasification, hydrothermal gasification, and anaerobic digestion, are being explored as potential pathways to improve the overall sustainability of waste management.
Existing scientific studies have largely focused on the conversion of individual waste types or on the application of a single technology to a specific waste stream, without accounting for regional integration, resource variability or systemic assessment. A city-scale analysis of waste streams could enable the identification of synergies between different waste types and the identification of optimal conversion pathways.
In this context, a key scientific challenge lies in the development of an integrated, multi-waste treatment framework capable of modelling, optimizing, and assessing a multi-waste, multi-product energy system at the city scale. The objective of this PhD project is to investigate waste treatment at the city scale, accounting for the seasonality of waste generation, waste stream composition, and local energy demand (heat, electricity, and gas). The work will consider local and European regulations (Waste Framework Directive, AGEC law, and RED III directive) as well as techno-economic and environmental aspects. The study will focus on one to three representative geographic areas and will establish a methodology that can be further applied to a broad range of territorial contexts.
Hydrogen transport and trapping in austenitic alloys coupling experiments and simulations.
Molecular hydrogen H2 is an alternative energy carrier to traditional fossil fuels, gas or oil. It meet the current energy and environmental challenges, i.e. the need to store greenhouse gases free energy produced by intermittent means such as wind turbines or solar panel. Nevertheless, its safe storage and transportation is one of the keys to its use. The containers or pipes that carry the hydrogen must be leaktight and maintain their integrity over time, for both economical and safety reasons. Understanding and predicting the behavior of hydrogen in container/pipeline alloys and the associated mechanical degradation – such as embrittlement – is therefore crucial for the development of the hydrogen industry. These issues are also generic to all alloys exposed to a source of hydrogen, in corrosion or in the metallurgical industries where the hydrogen simply comes from contact with water, or in the oil&gas industry where hydrogen comes from hydrogen sulphides present in hydrocarbons.
If many experimental works have identified hydrogen embrittlement as the origin of the degradation of alloys exposed to hydrogen, large gray areas still remain on the mechanisms at work due to experimental difficulties and the great variability of the observed phenomena. In addition, the transport and trapping of hydrogen prior to mechanical degradation are poorly known and poorly documented at the nanoscale.
The objective of the thesis is to explore the mechanisms of hydrogen trapping / transport in austenitic materials, as well as its distribution in volume, prior to cracking in order to be able to report and explain the experimental observations.
To achieve this objective, the thesis work will be dedicated to the study of pure nickel, a model system for the austenite phase. The study will be carried out in three stages: (i) thermodesorption measurements and (ii) atomic scale simulations using molecular dynamics, both feeding chemical kinetics modeling coupled with Fick's law at the mesoscopic scale.
AI model deployment using Hardware-Aware on-chip Fine Tuning
Emerging unconventional hardware technologies are essential for future Edge-AI applications, but they often suffer from variability, mismatches, and technology dispersion. These non-idealities can strongly reduce AI inference accuracy if no fine-tuning or calibration is applied. Traditional supervised fine-tuning is difficult to industrialize because it raises issues related to data confidentiality, service quality, software complexity, and hardware constraints.
This PhD project aims to develop hardware-algorithm co-design methods that avoid the need for fully supervised on-chip retraining. The main goal is to create task-agnostic, inference-level self-calibration strategies able to compensate hardware mismatches at the system level. The work will study existing adaptation methods, including weight-based, feature-based, output-based, and domain adaptation approaches.
The project will define a relevant Edge-AI application, develop a generic fine-tuning method, and validate it through low-level electrical simulations. If possible, the proposed algorithm may also be tested experimentally on a custom ASIC-based hardware setup.
Multiscale modeling of the magnetic response of heterogeneous material
The spectral dependence of the permeability of magnetic materials, whether in composite or dense materials, remains a complex issue due to the different scales of the phenomena involved. Approximate analytical models are often used to describe the frequency response of magnetic materials, particularly to improve their performance in areas such as power electronics. Recent results have shown that micro-magnetism codes can now predict the response of a system of coupled nanoparticles or a particle representing the volume of the materials in question. This thesis aims to use these tools to improve existing analytical models. An inclusion immersed in an effective field will be the paradigm from which the domain structure and the spectral response of the particle will be calculated using a micro-magnetism code. The materials studied include spherical particles or those with a high aspect ratio (magnetic oxides, ferromagnetic petals) at varying concentrations, ranging from dilute media to dense materials. This work will identify pathways to optimize the microstructure of materials for better performance in applications such as power electronics and microwave components. To this end, CEA provides a scientific computing environment with access to HPC resources, as well as facilities for sample preparation and static and dynamic magnetic characterization. At the end of this work, the candidate will have gained a solid understanding of the microstructure-property relationships described by a numerical approach applied to magnetic materials. More generally, this approach is expanding in the field of materials to improve their properties in various fields, under the designation "materials by design".
Self-calibrated mmW Injection Locked Oscillators
In our research group we have developed and used during the last few year an innovative technique for frequency generation where the injection locked oscillator are the core. However, this circuits that we found in electronics, but also in other disciplines such as mechanics, biology and fundamental physics, hide still some secrets.
In this PhD you will be starting with the existing knowledge about these circuits leveraging in the broad experience of the research team and you will contribute to extend this knowledge to understand the impact of external perturbations and manufacturing tolerances on the operation of such circuit, for next proposing and implementing self-calibration and stabilization techniques.
The. applications of this circuits are broad, but some of the most appealing are found in the field of high-speed mmW wireless and wired links, extremely high resolution radar, vital signs detection for medical applications and quantum experiments (such as resonant paramagnetic spectrometry.
Depending on the advancement of the research the proposed self-calibration technique will be applied in one of the existing developments in our group in one of these fields.
Modeling the CSS growth of CsPbBr3
Lead-halide perovskites, particularly CsPbBr3, are emerging as promising materials for X-ray detection in medical applications. This technology requires their deposition in thick layers (>100 µm), and close-space sublimation (CSS), initially developed by CEA-Liten, has shown highly encouraging results. However, this process remains poorly understood at the microscopic scale, and the relationship between microstructure and performance remains a major scientific and industrial challenge.
This thesis, in partnership with the SIMAP laboratory, aims to develop a comprehensive thermodynamic model of the CSS process. The candidate will (i) experimentally generate the essential thermodynamic data for modeling, (ii) simulate growth mechanisms, and (iii) validate them experimentally using dedicated instrumented growth furnaces and advanced characterization techniques. Machine learning tools will be implemented to establish predictive correlations between deposition parameters and layer properties.
The results will enable optimization of CsPbBr3 growth for more sensitive and stable X-ray detectors, with a strong impact on medical imaging. This work will also provide opportunities for high-impact publications and patents in a highly competitive field.
CdTe for medical radiography; control of electrical properties
The use of direct-conversion detectors in medical radiography opens up new possibilities. Due to its properties, the semiconductor material CdTe has emerged as the material of choice for manufacturing these new components. The proposed thesis topic aims to develop the knowledge and processes necessary to produce CdTe crystals with properties tailored to specific application requirements. The work will draw on the laboratory’s advanced expertise in mastering CdTe single-crystal growth processes. The key challenges of the project will be as follows:
- Performing annealing under controlled atmospheres (ex-situ, on small samples) to study their impact on the electrical properties of CdTe,
- Conducting advanced characterizations to better understand the doping mechanisms in CdTe,
- Fabricating “simple” devices and testing them under X-ray flux to quantify the performance of the laboratory’s materials.
The proposed thesis topic is central to the development of a CdTe technology for medical radiography applications. Multidisciplinary work (material and process development, material characterization, fabrication and X-ray testing of simplified devices) is proposed to address this topic.