Atomic layer deposition of TbF₃ thin films

Lanthanide fluoride thin films have gained interest as materials for various optical applications, including electroluminescent displays and mid-IR lasers. However, the number of atomic layer deposition (ALD) processes for lanthanide fluorides has remained low. In this work, we present an ALD process for TbF₃ using tris(2,2,6,6-tetramethyl-3,5-heptanedionato)terbium and TiF₄ as precursors. The films were grown at 175–350 °C. The process yields weakly crystalline films at the lowest deposition temperature, whereas strongly crystalline, orthorhombic TbF₃ films are obtained at higher temperatures. The films deposited at 275–350 °C are exceptionally pure, with low contents of C, O, and H, and the content of titanium is below the detection limit (<0.1 at. %) of time-of-flight elastic recoil detection analysis (ToF-ERDA). Due to the lack of titanium impurities, the films show high transmittance down to short UV wavelengths.