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

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. 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 AlBN. Wurtzite AlBN has a wurtzite  structure at room temperature, it is compatible with III-V semiconductors, can have a very high polarization (150 mC/cm2) and a high breakdown field up to 8 MV/cm allowing devices to sustain up to 1000 V. We expect that an applied field resulting from the ferroelectric 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, charge trapping/dissipation, internal fields. 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 including 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 [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 former will be measured by control MEM-LEEM experiments on AlN reference sample, allowing to resolve the magnitude of the polarization in the ferroelectric AlBN films.

Model interfaces will be fabricated in close collaboration with at the Air Force Research Laboratories (AFRL, Dayton, OH, USA). At the AlBN/Ga2O3 interface the doping level of the Ga2O3 will play a key role in screening the ferroelectric polarization of AlBN. This interface bottleneck may be overcome by the AlBN/GaN interface which will form the second family to be studied. Epitaxial growth will be targeted to reduce the possibility of charge trapping at the AlBN/GaN interface. Instead, interface chemistry is expected to play a more important role in determining the band line-up. An alternative solution to the interface charge and screening problem of AlBN/Ga2O3 may be the introduction of a floating W electrode in the AlBN/Ga2O3 stack, similar to the FeMFET geometry envisaged for non-volatile ferroelectric memories [Seidel2022]. This may allow screening of the polarization while maintaining the coupling with the band structure of Ga2O3. In this way the ferroelectric AlBN will polarize the W layer in much the same way as a floating gate, the potential induced in the W layer can couple with the electronic bands in the Ga2O3.

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

1. Successful growth of thin film ferroelectric AlBN

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 knowledge of Ga2O3 and GaN growth and the CEA expertise in characterization of surfaces and interfaces of ferroelectric materials is a unique combination in the Ga2O3 research community 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.

References

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

[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

[Seidel2022] K. Seidel et al., VLSI 2022, 355 https://doi:0.1109/VLSITechnologyandCir46769.2022.9830141

Les équipes de l’IRAMIS mènent des recherches en physique et chimie, au carrefour des mondes académiques et des missions du CEA, ainsi que des enjeux sociétaux et de l’innovation. Ses recherches portent sur les nouvelles technologies pour l’énergie, les technologies quantiques, les nouveaux matériaux, les systèmes complexes et l’interaction rayonnement-matière.

De nature principalement fondamentale, les recherches, menées à l’Institut sont ouvertes sur la création de valeur économique et le transfert technologique. Pour conduire ces recherches, les équipes de l’IRAMIS mettent en œuvre des installations et équipements scientifiques de premier plan et sont aussi très actives autour des Grands Instruments Européens.

The current research themes of the recruiting laboratory, a joint CEA-CNRS laboratory, cover oxide band structure, thin film topological insulators, surface and interface chemistry, ferroelectric and multiferroic films. The development of nanometric spectroscopic imaging for fundamental and applied science is a main theme of research. The main focus of the laboratory is the advanced characterization of ferroelectric based structures for integration into future electronics.

Strong grounding in solid state physics is essential. Taste and capacity for experimental physics