Symmetry engineering of two-dimensional In₂Se₃ semiconductors

https://www.c2n.universite-paris-saclay.fr/fr/

Symmetry engineering of two-dimensional In₂Se₃ semiconductors

Scientific project: How do atomic stacking and ferroelectric polarization shape the properties of an atomically thin semiconductor? Layered In₂Se₃ provides a platform to address this question: its α and β phases exhibit distinct structures and electronic properties, while rhombohedral (3R) stacking introduces an additional source of inversion-symmetry breaking. Distinguishing structural non-centrosymmetry from switchable ferroelectric polarization is a central challenge for future non-volatile nanoelectronic devices.

This internship is part of RHOMBO2D, an ANR project accepted in 2026 bringing together C2N, MPQ, IPCMS and SPINTEC. The student will contribute to the growth and characterization of thin In₂Se₃ layers, with emphasis on phase identification, thickness and crystal symmetry. Chemical vapor deposition (CVD) growth at C2N will be combined with Raman spectroscopy and polarization-resolved second-harmonic generation (SHG). Comparing α- and β-phase samples, including before and after controlled annealing, will help identify optical signatures of phase changes and symmetry breaking.

The expected outcome is a comparative set of Raman and SHG measurements linked to thickness and growth or annealing conditions. This will provide a basis for selecting samples for electronic and ferroelectric investigations. A continuation towards a PhD within RHOMBO2D is envisaged, extending the work to electronic band structure, quantum confinement and the interplay between stacking and polarization.

Methods and techniques: The student will be trained in CVD growth, sample preparation, atomic force microscopy (AFM), micro-Raman spectroscopy and polarization-resolved SHG mapping. Reference exfoliated crystals and MBE-grown films from SPINTEC will support comparisons. Results will be discussed alongside first-principles calculations and complementary structural measurements within the consortium. The PhD would offer opportunities for X-ray and angle-resolved photoelectron spectroscopy (XPS/ARPES), including synchrotron experiments, and collaboration on ferroelectric and transport measurements. SHG will be used as a symmetry probe; polarization switching requires complementary ferroelectric measurements.

References

[1] W. Ding et al., “Prediction of intrinsic two-dimensional ferroelectrics in In₂Se₃ and other III₂–VI₃ van der Waals materials”, Nature Communications 8, 14956 (2017).

[2] G. Kremer et al., “Mexican-Hat-Like Valence Band Dispersion and Quantum Confinement in Rhombohedral Ferroelectric α-In₂Se₃”, Physical Review B 112, 155418 (2025).

[3] M. Rahimi et al., “Probing the Electric and Thermoelectric Response of Ferroelectric 2H and 3R α-In₂Se₃”, Applied Physics Letters 124, 253503 (2024).

Possibility to continue with a PhD? Yes, within the RHOMBO2D project.

Envisaged PhD funding: ANR RHOMBO2D — project accepted in 2026.

étudiant en M2/ Physique/Chimie et Matière condensé

interssé par une thèse financé par l'anr