Deep UV-LEDs based on digital alloys (GaN)n/(AlN)m
Context :
Group-III nitride semiconductors (GaN, AlN, InN) are renowned for their outstanding light emission properties. For more than two decades, they have powered the blue and white LEDs used worldwide, thanks to highly efficient InGaN quantum wells (external quantum efficiency > 80%). In contrast, UV LEDs based on AlGaN quantum wells are still very inefficient (< 10%) and only recently became commercially available. Overcoming this limitation is a key challenge in optoelectronics: achieving efficient deep-UV emission (220–280 nm) would enable high-performance bactericidal applications such as water purification, surface sterilization, and virus inactivation.
Recently, two breakthrough concepts are promising to explore for UV-LEDs:
1. Deep-UV emission from GaN monolayers in AlN: Grow a few atomic monolayers (MLs) of GaN embedded in an AlN matrix. This extreme quantum confinement leads to deep-UV emission down to 220 nm. High emission efficiency is expected due to strong exciton binding, stable even at room temperature
2. Enhanced doping using graded digital GaN/AlN alloys: Use graded digital alloys (GaN)?/(AlN)? where n and m are the number of atomic layers. This architecture enables efficient n- and especially p-type doping, which is a major bottleneck in AlGaN. GaN is much easier to dope than AlN, making this approach very promising for device fabrication.
Scientific Targets :
The aim is to master monolayer growth using MOVPE (metal-organic vapor phase epitaxy), the most industrially relevant technique :
- M2 project: develop the growth of GaN monolayers on AlN substrates, study their deep-UV emission properties, and optimize growth conditions for self-limited single-layer deposition.
- PhD continuation: design and fabricate doped digital GaN/AlN alloys to build the first efficient deep-UV LEDs based on this architecture.
Lab background and collaboration:
The group has long-standing expertise in visible and UV light emission from nitride nanowires. We have already demonstrated 280 nm emission from (GaN)?/(AlGaN)? digital alloys, proving the viability of this approach. The project will be highly experimental (epitaxy, advanced structural and optical characterization) and conducted in close collaboration with Institut Néel for cathodoluminescence analysis and device processing.
Why join this project ?
Gain expertise in epitaxy, semiconductor physics, and optoelectronics. Work in a dynamic, collaborative environment with strong ties to industry. Contribute to the development of the next generation of deep-UV LEDs.
Synthetic methodologies towards functionalized azaheterocycles and application to energetic molecules
The objective of the PhD is to develop new synthesis and/or functionalization methods to obtain functionalized heterocyclic molecules. These molecules are based on 5- or 6-member azaheteroaromatic rings (diazines, triazines, triazoles, tetrazoles, etc.). The targeted structures make it possible to envisage high densities and enthalpies of formation, while maintaining low sensitivity (thermal, mechanical, etc.). They find applications in the energy field, notably propulsion, explosives and gas generators (airbags). In addition, these heterocyclic compounds as well as the intermediates are also structurally close to families of biologically active products and/or likely to exhibit fluorescence properties, as already shown in a previous PhD in the laboratory.
Chemical recycling of oxygenated and nitrogenated plastic waste by reductive catalytic routes
Since the 1950s, the use of petroleum-based plastics has encouraged the emergence of a consumption model focused on the use of disposable products. Global plastic production has almost doubled over the last 20 years, currently reaching 468 million tons per year. These non-biodegradable plastic are the source of numerous forms of environmental pollution. Since the 1950s, only 9% of the wastes have been recycled. The majority have been incinerated or sent to landfill. In the current context of this linear economy, health, climate and societal issues make it essential to transition to a circular approach to materials. This evolution requires the development of recycling methods that are both effective and robust. While the most common recycling methods currently in use are mainly mechanical processes that apply to specific types of waste, such as PET plastic bottles, the development of chemical recycling methods appears promising for treating waste for which no recycling channels exist. These innovative chemical processes make it possible to recover the carbonaceous material from plastics to produce new ones.
Within this objective of material circularity, this doctoral project aims to develop new chemical recycling routes for mixed oxygen/nitrogen plastic waste such as polyurethanes (insulation foam, mattresses, etc.) and polyamides (textile fibres, circuit breaker boxes, etc.), for which recycling routes are virtually non-existent. This project is based on a strategy of depolymerizing these plastics by the selective cleavage of the carbon-oxygen and/or carbon-nitrogen bonds to form the corresponding monomers or their derivatives. To do that, catalytic systems involving metal catalysts coupled with abundant and inexpensive reducing agents will be developed. In order to optimize these catalytic systems, we will seek to understand how they proceed and the mechanisms involved.
Blended positive electrodes in solid-state batteries: Effect of the electrode fabrication process on electrochemistry
The development of cost-effective, high-energy-density solid-state batteries (SSBs) is essential for the large-scale adoption of next-generation energy storage technologies. Among various cathode candidates, LiFePO4 (LFP) and LiFe1??Mn?PO4 (LFMP) offer safety and cost advantages but suffer from low working voltages and limited kinetics compared to Ni-rich layered oxides such as LiNi0.85Mn0.05Co0.1O2 (NMC85). To balance energy density, rate capability, and stability, this PhD project aims to develop blended cathodes combining LFMP and NMC85 in optimized ratios for solid-state configurations employing sulfide electrolytes (Li6PS5Cl). We will investigate how fabrication methods- including slurry-based electrode processing and binder-solvent optimization- affect the electrochemical and structural performance. In-depth operando and in situ characterizations (XRD, Raman, and NMR) will be conducted to elucidate lithium diffusion, phase transition mechanisms, and redox behavior within the blended systems. Electrochemical impedance spectroscopy (EIS) and titration methods will quantify lithium kinetics across various states of charge. By correlating processing conditions, microstructure, and electrochemical behavior, this research seeks to identify optimal cathode compositions and manufacturing strategies for scalable, high-performance SSBs. Ultimately, the project aims to deliver a comprehensive understanding of structure–property relationships in blended cathodes, paving the way for practical solid-state battery technologies with enhanced safety, stability, and cost efficiency.
Growth and Characterization of AlScN: A New Promising Material for Piezoelectric and Ferroelectric Devices
III-nitride semiconductors — GaN, AlN, and InN — have revolutionized the lighting market and are rapidly entering the power electronics sector. Currently, new nitride compounds are being explored in the search for novel functionalities. In this context, aluminum scandium nitride (AlScN) has emerged as a particularly promising new member of the nitride family. Incorporating scandium into AlN leads to:
* Enhanced Piezoelectric Constants: Making AlScN highly attractive for the fabrication of piezoelectric generators and high-frequency SAW/BAW filters.
* Increased Spontaneous Polarization: The enhanced polarization can be exploited in designing high-electron-mobility transistors (HEMTs) with very high channel charge densities.
* Ferroelectricity: The recently discovered (2019) emergence of ferroelectric properties opens up possibilities for developing new non-volatile memory devices.
Over the past five years, AlScN has become a major focus of research, presenting numerous open questions and exciting opportunities to explore.
This PhD thesis will focus on the study of the growth and properties of AlScN and GaScN synthesized by molecular beam epitaxy (MBE). The student will receive training in the use of an MBE system for the synthesis of III-nitride semiconductors and in the structural characterization of materials using atomic force microscopy (AFM) and X-ray diffraction (XRD). The variation of the polarization properties of the materials will be investigated by analyzing the photoluminescence of quantum well structures. Finally, the student will be trained in the use of simulation software to model the electronic structure of the samples, aiding in the interpretation of the optical results.
Development of photo-printed interferometric biosensors on multi-core optical fibers for molecular diagnostics
Optical fibers are minimally invasive devices commonly used in medicine for in vivo tissue imaging by endoscopy. However, at present, they only provide images and no molecular information about the tissues observed. The proposed thesis is part of a project aimed at giving optical fibers the ability to perform molecular recognition in order to develop innovative biosensors capable of performing real-time, remote, in situ, and multiplexed molecular analysis. Such a tool could lead to significant advances in the medical field, particularly in the study of brain pathologies, where knowledge of the tumor environment, which is difficult to access using conventional biopsies, is essential.
The proposed approach is based on 2-photon polymerization printing of interferometric structures at the end of each core of a multifiber assembly. The detection principle is based on the interference occurring in these structures and their modification by the adsorption of biological molecules. Each fiber in the assembly will act as an individual sensor, and measuring the intensity of the light reflected at the functionalized end will provide information about the biological interactions occurring on that surface. By modeling the interference phenomenon, we determined parameters to optimize the shape and sensitivity of interferometric structures (PTC InSiBio 2024-2025). These results enabled the printing and characterization of the sensitivity of interferometric structures on single-core fibers. The objectives of the thesis are to continue this optical characterization on new samples and to develop original photochemical functionalization methods in order to graft several biological probes onto the surface of the fiber assemblies. This multi-functionalization will enable multiplexed detection, which is essential for future medical applications. Depending on the progress of the thesis, the biosensors will be validated through the detection of biological targets in increasingly complex environments, up to and including a brain tissue model.
Coupled Friction Effects of Dirac sea and Electromagnetic Vacuum on Atomic movements
Quantum fluctuations induce conservative macroscopic forces such as the Casimir effect. They could also cause dissipative forces, termed vacuum (or quantum) friction. Up to now, this friction effect has been calculated with consideration of the electromagnetic fluctuations only, i.e. without taking into account the Dirac Sea. This project is devoted to the extension of our research in this direction: electrons, as main contributors of the matter-field interaction, also interact with electron-positron virtual pairs in the quantum vacuum. How much of quantum friction, at zero or finite vacuum temperature, could be due to this type of interaction? A first step will be adapting the present semi-classical framework to include vacuum polarization and pair creation. In doing so, one will encounter finite frequency cut-offs, traditionally linked to virtual pair creation; thus one will determine a friction component linked with the finite cut-off of Fourier integrals. On this research path, one shall pay attention to maintaining the mathematical coherence of the whole framework. A longer-term goal remains a complete and consistent quantum relativistic treatment of quantum friction at the atomic level.
Modeling of a magnonic diode based on spin-wave non-reciprocity in nanowires and nanotubes
This PhD project focuses on the emerging phenomenon of spin wave non-reciprocity in cylindrical magnetic wires, from their fundamental properties, to their exploitation towards realizing magnonic diode based devices. Preliminary experiments conducted in our laboratory SPINTEC on cylindrical wires, with axial magnetization in the core and azimuthal magnetization on the wire surface, revealed a giant non-symmetrical effect (non-symmetrical dispersion curves with different speeds and periods for left- and right-propagating waves), up to an extent of creating a band gap for a given direction of motion, related to the circulation of magnetization (right or left). This particular situation has not been yet described theoretically or modeled, which sets an unexplored and promising ground for this PhD project. To model spin-wave propagation and derive dispersion curves for a given material we plan to use different numerical tools: our in-home 3D finite element micromagnetic software feeLLGood and open source 2D TetraX package dedicated to eigen modes spectra calculations. This work will be conducted in tight collaboration with experimentalists, with a view both to explain experimental results and to guide further experiments and research directions.
Mapping surface potentials of catalytically activated metal oxide photoanodes
During photoelectrolysis (or solar water splitting), charge transfer at the photoanode / electrolyte interface is determined by the alignment between energy bands, both at the electrode and electrolyte side. Surface potential of the electrode plays a major role on the final band bending and thus charge separation at the interface. Also called electrochemical surface potential, it varies as a function of material environment (vacuum, air, water, etc.). The objective of this thesis is to address the OER (Oxygen Evolution Reaction) at the photoanode / electrolyte interface in terms of energy bands and in particular from the electrochemical surface potential perspective. Thus, during this thesis the student will characterize surface potentials of a series of catalytically activated metal oxide photoanodes in contact with different environments (vacuum, variable humidity air, water) and correlate it to photoelectrochemical activity. PhD student’s activity will be structured around fours axes: i) synthesis of photoanodes; ii) photoelectrochemical activity characterization; iii) characterization by atomic force microscopy (AFM) correlated with Kelvin force microscopy (KPFM); iv) synchrotron X-ray spectromicroscopies (STXM, XPEEM) and near ambient pressure photoemission (NAP-XPS). The student will be hosted at the SPEC laboratory at CEA-Saclay for the duration of the thesis. HisHer work is part of a long-standing collaboration between SPEC and SOLEIL.
Multi-modal in situ nuclear magnetic resonance analysis of electrochemical phenomena in commercial battery prototypes
Advancing electrochemical energy storage technologies is impossible without a molecular-level understand-ing of processes as they occur in practical, commercial-type devices. Aspects of the battery design, such as the chemistry and thickness of electrodes, as well as configurations of current collectors and tabs, influence the electronic and ionic current density distributions and determine kinetic limitations of solid-state ion transport. These effects, in turn, modulate the overall battery performance and longevity. For these reasons, optimistic outcomes of conventional ‘coin’ cell tests often do not converge into high-performance commercial cells. Safety concerns associated with high energy density and flammable components of batteries are another subject paramount for conversion from fossil to green energy sources.
Nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI) are exceptionally sensitive to the structural environment and dynamics of most elements in active battery materials.
Recently, plug-and-play NMR and surface-scan MRI methods have been introduced. In the context of fun-damental electrochemical research, merging two innovative complementary concepts within one multi-modal (NMR-MRI) device would enable diverse analytical solutions and reliable battery performance metrics for academia and the energy sector.
In this project, an advanced analytical framework for in situ analysis of fundamental phenomena such as sol-id-state ion transport, intercalation and associated phase transitions, metal plating dynamics, electrolyte deg-radation and mechanical defects in commercial Li- and Na-ion batteries under various operational conditions will be developed. A range of multi-modal (NMR-MRI) sensors will be developed and employed for deep analysis of fundamental electrochemical processes in commercial battery cells and small battery packs.