Epitaxial Synthesis of Highly Oriented 2D Janus Rashba Semiconductor BiTeCl and BiTeBr

"Janus" 2D crystals Bismuth Tellurohallides (BiTeX, X=Cl, Br, I) are stacked layers of X, Bi and Te planes. The members of this family show giant Rashba spin splitting, which makes them ideal candidates for room temperature spintronics without the need of an external magnetic field¹. Previous experimental studies of BiTeX were performed on the exfoliated samples from bulk BiTeX, which is non-scalable and lacks reproducibility². No thin film growth with controlled thickness and orientation has been reported, which is essential to explore the atomic level phenomena and device integration. Here, the first epitaxial growth of highly crystalline and orientation controlled BiTeCl and BiTeBr is reported which was achieved by a two-step conversion process. The synthesis method includes the physical vapor deposition of Bi₂Te₃ nanosheets on c-cut sapphire and next, conversion of the Bi₂Te₃ sheets to BiTeCl(Br) by exposure to BiCl(Br)₃ vapor. The existence and uniformity of Janus BiTeX was confirmed by Raman mapping of A¹₁ vibrational mode  and energy dispersive X-ray spectroscopy after conversion. Stability of these Janus sheets was also studied by time dependent Raman spectroscopy. Overall, this work offers a new pathway to synthesize few layers of Janus compounds.

¹Kovács-Krausz, Zoltán, et al. Nano letters 20.7(2020):4782-4791

²Jacimovic, J., et al. Scripta Materialia 76(2014):69-72