Van der Waals Growth of Ferroelectric GeTe Thin Films by Industrial Magnetron Sputtering for Large-Scale Integration

Chalcogenide materials have attracted a lot of attention over the years due to their wide range of applications. Among them, some compounds such as Ge-Sb-Te based alloys exhibit a unique portfolio of properties, which has led to their wide use for non-volatile phase-change memory applications [1,2]. In addition to memory applications, the GeTe phase-change alloy is also very promising for RF switches [3], for thermoelectrics [4,5], and offers numerous opportunities for optical applications[6] and photonics[7] as well as for the emerging field of spinorbitronics [8]. GeTe has also been the subject of numerous studies, , due to the ferroelectric character of the stable rhombohedral α phase and the existence of a reversible structural transformation (around 430°C) between the rhombohedral α phase and the cubic paraelectric cubic b phase. The rhombohedral α-GeTe phase can be described as a deformed rocksalt structure that has undergone shearing along a cube diagonal ([111] or equivalent direction), with a relative displacement of the Ge and Te atoms along this direction, which is . responsible for the ferroelectric properties. In the α-GeTe phase a Ge atom is surrounded by six Te atoms forming a distorted octahedron with three short and three long Ge-Te bonds. This splitting is interpreted as resulting from a Peierls distortion. These properties have sparked interest in GeTe as a ferroelectric Rashba semiconductor, combining semiconductivity, strong spin-orbit coupling and non-volatility. In addition, GeTe has recently attracted renewed interest with the demonstration of non-volatile ferroelectric control of spin-charge conversion in epitaxial germanium telluride films deposited by molecular beam epitaxy [8]. The sign of the charge current can be controlled by the orientation of the ferroelectric polarization, which can be switched by an electric gate despite the high intrinsic carrier density of GeTe. In this context, the successful deposition of high-quality epitaxial ferroelectric GeTe films using a large-scale industrial deposition process could open up a new field of applications based on the non-volatile electrical control of spin currents in semiconducting GeTe. In this presentation, I will show that the van der Waals growth of high structural quality ferroelectric GeTe thin films using industrial magnetron sputtering could be achieved, demonstrating that this material could be monolithically integrated on silicon for devices beyond CMOS such as reconfigurable spin-based and in-memory computing devices.<br/><br/><b>Key words</b>: chalcogenide, GeTe, phase-change material, van der Waals epitaxy, ferroelectric<br/><br/><b>REFERENCES</b><br/>1. P. Noé, et al., Semicond. Sci. Technol. <b>33</b>, 013002, (2018).<br/>2. P. Noé and F. Hippert, “Structure and Properties of Chalcogenide Materials for PCM”, in Phase Change Memory: Device Physics, Reliability and Applications, A. Redaelli, Éd. Cham: Springer International Publishing, 2018, p. 125–179.<br/>3. R. M. Young, et al., 2018 IEEE/MTT-S International Microwave Symposium – IMS, pp. 832–835 (2018).<br/>4. J. Li, et al., J. Am. Chem. Soc. 140, 16190–16197 (2018).<br/>5. Q. Tian, et al., Nanoscale 13, 18032–18043 (2021).<br/>6. P. Martinez, et al., Adv. Mater. 32, 2003032 (2020).<br/>7. J. Wang, et al., IEEE Access 8, 121211 (2020).<br/>8. S. Varotto, et al., Nat. Electron. 4, 740–747 (2021).