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.