We are looking for highly motivated candidates to work on our projects

PhD and Post-doc positions below

contact : nick.barrett@cea.fr

Post-doctoral positions

• Ferro4Power

Title: Interface physics of ferroelectric AlBN/Ga2O3 and AlBN/GaN stacks for power electronics

Domain, Specialties: Material physics, surface science

Keywords: AlBN, GaN, Ga2O3, power electronics, interfaces, HAXPES, XPS

Location: Laboratory for the Study of NanoStructures and Surface Imaging (LENSIS) at CEA Saclay, France

Type of contract: 20-month Postdoc, expected start date Feb/Mar 2027

Description

Commercial aviation accounts for about 2.5% total world CO2 emissions (1bT). A true, long-term, clean perspective eliminating a significant part of CO2 emissions is electric but current passenger payload limit (<100) is a major obstacle. One viable solution could be the hybrid airplane in which gas turbines are used for take-off and landing (while simultaneously charging batteries) and in-flight cruising is electrically powered. Progress in electric air travel is accelerating. The Scottish company, Loganair, will become Europe's first commercial airline operating an electric [LOG].

However, weight and MW power constraints require high voltage components. Fundamental research is required to optimize materials for integration into electronic components, capable of sustaining these power ratings.

Ga2O3 belongs to the family of ultra-wide band gap semiconductors with potentially unrivalled performance in power electronics thanks to breakdown fields EBD up to 8-12 MV/cm. GaN is a III-V semiconductor already employed in power electronics [ST], particular for high electron mobility transistors (HEMTs using AlGaN/GaN interfaces). The high mobility (2000cm2/Vs), band gap (3.2 eV), breakdown field (3.3 MV/cm can support up to 1000 V in HEMT architectures. In addition, the very low on-resistance allows more aggressive scaling.

The original idea of the Ferro4Power proposal is to increase the range of applications of Ga2O3 and GaN based devices by introducing a high breakdown, power electronics compatible, ferroelectric layer into the device stack. The up or down polarization state of the ferroelectric layer will provide an electric field capable of modulating the Ga2O3 and GaN valence and conduction bands, and hence the properties of possible devices, such as Schottky diodes (SBD), hybrid depletion mode transistors for Ga2O3 and high frequency HEMTs for GaN. Our hypothesis is to control the electronic bands of Ga2O3 and GaN using an adjacent, ferroelectric AlBN layer. AlBN has a wurtzite structure at room temperature, can be epitaxially compatible with III-V semiconductors, has a very high ferroelectric polarization (150 mC/cm2) and a high breakdown field up to 8 MV/cm allowing typical power devices to sustain up to 1000 V. We expect that an applied field resulting from the polarization of an adjacent layer will not only shift the band structure but also populate or depopulate charge carrier density by modifying the orbital occupancies and localization making up the valence and conduction bands.

We will explore the chemistry and electronic structure of AlBN/Ga2O3 and AlBN/GaN interfaces, focusing on the key phenomena of polarization screening and charge trapping/dissipation. The project will use advanced photoelectron spectroscopy techniques including synchrotron radiation induced Hard X-ray photoelectron spectroscopy and Photoemission electron microscopy as well as complementary structural analysis which may include high-resolution electron microscopy, X-ray diffraction and near field microscopy. Using appropriate, low energy, ion beam etching and angular dependence of the XPS, the AlBN/ Ga2O3 or AlBN/GaN interfaces will be studied following the methods we have already developed for hafnia-based stacks [Hamouda2020, Hamouda2022]. Hard X-ray photoemission (HAXPES) using synchrotron radiation will be used to probe the interface chemistry and band alignment in stacks integrating AlBN on Ga2O3 or GaN in a non-destructive manner (Fig. 2).

We will design samples with suitable geometry for operando measurements of the interface band line-ups as a function of the applied bias or the AlBN polarization state [Gueye2017]. Operando experiments following the polarization wake-up sketched in Fig. 3 will be carried out to characterize the internal field strength as a function of polarization [Boucly2025].

Low-energy electron microscopy (LEEM) is particularly suited to probe the surface potential [Barrett2013]. At the surface of AlBN the difference in electron affinity of Al or N termination layer adds to the surface potential modulation due to the P↑ or P↓ polarization. The Al/N contrast will be measured by MEM-LEEM experiments on AlN reference sample, allowing to resolve the magnitude of the polarization in the ferroelectric AlBN films.

Figure 4. Schematic of LEEM analysis of a ferroelectric film with upward (P↑) and downward (P↓) polarized domains. The polarization discontinuity at the surface modulates the surface potential and hence the position of the MEM-LEEM transition.

Model interfaces will be fabricated in close collaboration with at the Air Force Research Laboratories (AFRL, Dayton, OH, USA), first on simple capacitor stacks, then on AlBN/Ga2O3 and AlBN/GaN HEMT-like heterostructures. Further samples are foreseen at the materials dept of the University California Santa Barbara (UCSB) by molecular beam epitaxy.

The four objectives of the project can be summarized as follows:

1. Successful growth of thin film ferroelectric AlBN, electrical characterizations

2. Correlation of physical chemistry and electrical properties of W/AlBN/W capacitors

3. Ferroelectric control of band alignment in AlBN/ Ga2O3 stacks

4. Ferroelectric control of band alignment in AlBN/GaN stacks

The synergy of the AFRL and UCSB knowledge of Ga2O3 and GaN growth and the CEA expertise in characterization of surfaces and interfaces of ferroelectric materials is a unique combination and as such promises to attract some high-profile interest as well as added scientific value for both laboratories.

The results should therefore be of interest not only to physicists studying fundamental aspects of functionality in artificial heterostructures but, thanks to the operando approach, they should also attract interest from engineers working in R & D applications of power electronics.

Skills:  Strong grounding in solid state physics is essential. Mobility required for synchrotron work (Europe and USA)

How to apply: Candidates should send a CV, cover letter and contact details for two referees to the e-mail addresses in the contact information.

Links: www.lensislab.com
              iramis.cea.fr/spec/lensis

Contact

Nick BARRETT
Phone: 01 69 08 32 72
Email: nick.barrett@cea.fr

Lucia PEREZ RAMIREZ
Phone: 01 69 08 47 27
Email: lucia.perezramirez@cea.fr

References
[GEA] General Electric Aerospace Hybrid airplane https://www.youtube.com/watch?v=jBu9g6kab9M

[LOG] LoganAir BETA technologies https://www.loganair.co.uk/news/loganair-royal-mail-and-beta-technologies-complete-uks-first-electric-flight-demonstrations-across-scotland/

[ST] https://www.st.com/en/applications/energy-generation-and-distribution/ev-charging-dc-fast-charging-stations.html

[Hamouda2020] W. Hamouda et al., J. Appl. Phys. 127, 064105 (2020) https://doi.org/10.1063/1.5128502

[Hamouda2022] W. Hamouda et al., Appl. Phys. Lett. 120, 202902 (2022) https://doi.org/10.1063/5.0093125

[Kraut1980] J. E. A. Kraut, R. W. Grant, and S. P. Eowalczyk, Phys. Rev. Lett. 44, 1620 (1980) https://doi.org/10.1103/PhysRevLett.44.1620

[Gueye2017] I. Gueye et al., Appl. Phys. Lett. 111, 222902 (2017) https://doi.org/10.1063/1.5004178

[Boucly2025] A. Boucly et al., Sci. Rep. 15, 8015 (2025) https://doi.org/10.1038/s41598-025-90555-6

[Barrett2013] N. Barrett et al., J. Appl. Phys. 113, 187217 (2013) https://doi.org/10.1063/1.4801968

[Zhu2022] W. Zhu et al., Adv. Electron. Mater. 8, 2100931 (2022) https://doi.org/10.1002/aelm.202100931

• ECHOES : Edge seCurity witH ferrOelectric dEviceS

Data centric applications such as artificial intelligence and IoT require to process a massive amount of Data. The energy overhead of data transfer to and from the cloud will rapidly become unbearable. To meet this challenge, edge computing is necessary. However, this also means that sensitive data may be stored and processed outside of traditional data centers, which can potentially expose it to security threats thus putting a strong emphasis on securing data in edge computing. In this context, emerging non-volatile memory technologies are potential candidates for secured NVM in future edge-devices thanks to their superior scalability and energy-efficiency as compared to Flash. Ferroelectric hafnia-based NVM are highly appealing because of their ultra-low power consumption (< 0.1pJ/bit)[4], high endurance (>1014) and the intrinsic stochasticity.

The goal of ECHOES is to determine whether hafnia-based FE NVM can outperform current NVM solutions for edge-security applications bring a comprehensive understanding of imprint through advanced characterization and physical modelling.

In particular, we will investigate the materials physics of hafnia-based capacitors which allow to minimize the hysteresis imprint via control of the oxygen vacancy distribution and the insertion of appropriate interface layers and thus maximize the hardware security.

Ferroelectric capacitors stacks will made at INL by physical vapor and atomic layer deposition (PVD and ALD). Advanced structural and electrical characterization on samples will provide crucial insights to feed and/or confirm the physical model

The post-doctoral research will use X-ray Photoelectron Spectroscopy (XPS, HAXPES) and PhotoEmission Electron Microscopy (XPEEM) to characterize the oxygen vacancy profiles near the electrode/ferroelectric interface and the interface chemistry and electronic structure in FeCAP test structures as a function of cycling. The intensive use of hard X-rays will allow analyzing devices with realistic top electrode thicknesses at synchrotron radiation centers in operando conditions using dedicated sample-holders. Microscopic FeCAPs will be characterized using both laboratory and synchrotron based XPEEM. Stochastic switching on sub micron test structures, fabricated by e-beam lithography on the NanoLyon platform of INL will be investigated by Piezoresponse Force Microscopy (PFM) at SPEC.

Partners

Institut des Nanotechnologies de Lyon (INL)

Institut Materials Microelectronic and Nanoscience of Provence (IM2NP)

Service de Physique de l’état condense au CEA (SPEC)

The post-doc contract is for 20 months, start date early 2026 preferred.

CV and contact details for two references before 30th November 2025 to Nick Barrett (nick.barrett@cea.fr)

• Ferrofutures : “plateForme fERROélectrique pour le calcUl embarqué critique : efficaciTé, peRformancES, adaptibilité

FerroFutures aims to demonstrate all of the scientific and technical elements required for the value chain of a future French ferroelectronics branch capable of responding to the needs of artificial intelligence at the edge.

Amongst emerging memory and logic technologies, ferroelectrics offer by far the best energy consumption, allowing access to low-cost non-volatile functionalities, several orders of magnitude more frugal than competitors.

FerroFutures will integrate this emergent techonology with innovative circuit and systems architectures for edge AI.

The post-doctoral research is an integral part of the optimization of a FeMFET, i.e. a ferroelectric capacitor (FeCAP) wired to the gate of a standard CMOS transistor. The FeCAP should show with low operating voltage, endurance better than 1012 cycles, non-destructive read, zero imprint.

The FeCAPs will be elaborated by physical vapor and atomic layer deposition (PVD and ALD). Structural characterization by X-ray diffraction and by atomic force microscopy will analyze the phase composition and grain size of the hafnia based films. The macroscopic electrical properties of the FeCAPs will be extracted from I-V, C-V and PUND measurements. Piezo-response force microscopy will provide information on the microscopic scale. The FeCAPs will then be studied using X-ray photoelectron spectroscopy (XPS) in the laboratory and by Hard X-ray photoemission (HAXPES) using synchrotron radiation. The latter will allow operando experiments to quantify the oxygen vacancy distribution as a function of endurance and polarization. Several synchrotrons will be used, including Soleil, Petra-III (Hamburg), Spring-8 (Japan) and NSLS-2 (Brookhaven, USA). The results will form an ensemble of physical characteristics to validate the fabrication processes and to provide experimental input to the modelling.

Partners

L’Université de Bordeaux (IMS)

Institut Materials Microelectronic and Nanoscience of Provence (IM2NP)

Institut des Nanotechnologies de Lyon (INL)

CEA/LETI

CEA/LIST

CEA IRAMIS (Service de Physique de l’état condense SPEC)

CV and contact details for two references before 31st July 2024 to Nick Barrett (nick.barrett@cea.fr)

To cope with the requirements of Artificial intelligence at the edge, new architectures have to be explored in the light of new emerging devices technologies. In the context of the Horizon Europe Ferro4EdgeAI collaborative project, we aims to develop and demonstrate from 1000X to 2500X energy efficiency gain with respect to cloud based CMOS for intelligent edge processors based on ferroelectric technology and the computation-in-memory paradigm.

The unique characteristics of FE technology [Silva2023] will be explored in the light of the targeted applications. The device technology at the heart of Ferro4EdgeAI is the FeFET-2 in which a ferroelectric capacitor is added in series with the gate stack of a conventional CMOS transistor (Figure). Conceptually this combines the simplicity and endurance/retention characteristics of the FeRAM with the plasticity and quasi-analogue response of the FeFET, without the adverse effects of charge trapping on endurance, retention, imprint and drift.

The primary objective of the materials aspect of Ferro4EdgeAI is the optimization of HfO2-based ferroelectric materials for multilevel functionality suitable for AI applications by investigating the trade-off in memory window, film thickness & stability of the ferroelectric state. We require a FE film which offers the possibility for a large memory window (large remanent polarization), able to retain the set polarization states.

The post-doctoral research will focus on the switching kinetics of films with different process parameters and switching voltages will be analysed via time-resolved X-ray photoemission spectroscopy (XPS, PEEM) with a time-resolved detector funded by the project to characterize ML switching.

Extensive use of synchrotron radiation is foreseen for the operando experiments. Samples will be supplied by NaMLab (Dresden) and the CEA LETI (Grenoble) who will also provide the integration.

In addition to the scientific research, the successful candidate will be expected to assist in project management and interact with all of the consortium partners, in particular for reporting and organization of regular project meetings.

The initial contract is for 22 months, June 2024 start date, negotiable

CV and contact details for two references before 31st March 2024 to Nick Barrett (nick.barrett@cea.fr)

[Silva2023] J.P.B. Silva et al, Roadmap on ferroelectric hafnia-and zirconia-based materials and devices APL Mater. 11, 089201 (2023)

[Vianello2019] Vianello, E., L. Perniola, and B. De Salvo. Emerging memory technologies for neuromorphic hardware Advances in Non-Volatile Memory and Storage Technology. Woodhead Publishing 585 (2019)

[Mulaosmanovic2018] H. Mulaosmanovic et al., Accumulative Polarization Reversal in Nanoscale Ferroelectric Transistors ACS Appl. Mater. Interfaces 10, 23997 (2018)