Sara VAROTTO
Spin-charge interconversion represents a promising viable solution for energy efficient electronics beyond CMOS architecture [1]. Broken inversion symmetry enables efficient and electrically tunable conversions. However, the electric field control remains volatile in semiconductors. This brought interest in ferroelectric Rashba semiconductors (FERSC), where semiconductivity, large spin–orbit coupling and non-volatility are intertwined.
The father compound of FERSCs is germanium telluride (GeTe), a CMOS-compatible semiconductor characterized by a giant Rashba-type spin-orbit coupling at room temperature, arising from the symmetry breaking induced by ferroelectric displacement. Importantly, calculations revealed that the spin orientation of each Rashba sub-band is inverted upon ferroelectric polarization reversal. We demonstrated such link in epitaxial GeTe(111) thin films on silicon, by our spin and angle resolved photoemission measurements on two surfaces with inward or outward spontaneous polarization [2]. Thus, FERSCs allow for ferroelectric control of the spin-resolved band structure in semiconductors, with intriguing implications on the spin transport properties.
Here we demonstrate the non-volatile, ferroelectric control of spin-to-charge conversion at room temperature in GeTe(111)//Si films [3]. First, we prove the feasibility of the ferroelectric switching, despite the high density of free carriers. The switching is induced by voltage pulses applied to a gate electrode, while the readout of the written state is performed by electro-resistive measurements of the GeTe/metal junction. By gate dependent spin-pumping at ferromagnetic resonance, we observe a spin-to-charge conversion as efficient as in Pt, and we show that its sign is switched for two opposite ferroelectric states. Density functional theory calculations reveal the consistency of these observation with spin Hall effect in thin GeTe films.
Our results open a route towards devices combining spin-based logic and memory integrated into a silicon-compatible material, where ferroelectricity can be employed as state variable to tune the spin-to-charge conversion.
[2] D. Di Sante et al., Adv. Mater. 25, 509-513 (2013)
[3] C. Rinaldi et al., Nano Letters, (2018); DOI: 10.1021/acs.nanolett.7b04829
[4] S. Varotto et al., arXiv:2103.07646 (2021)