Atomic and Molecular Layer Deposition of Functional Thin Films Based on Rare Earth Elements

High-quality rare earth element (R) based thin films are in demand for applications ranging from (opto)electronics and energy conversion/storage to medical diagnostics, imaging and security technologies. Atomic layer deposition (ALD) offers large-area homogeneous and conformal ultrathin films and is uniquely suited to address the requirements set by the potential applications of R-based thin films. The history starts from the 1990s, when the first electroluminescent R-doped thin films were grown with ALD. The interest soon expanded to rare earth element oxide layers as high-k gate dielectrics in semiconductor devices, and later to complex ternary and quaternary perovskite oxides with novel functional properties. The most recent advancements related to the combined atomic/molecular layer deposition (ALD/MLD) have rapidly expanded the family of R-organic hybrid materials with intriguing luminescence and up-conversion properties. This review provides up-to-date insights to the current state of ALD and ALD/MLD research of R-based thin films and highlights their application potential.