A New Synthetic Method for HfS 2 Thin Films Using MOCVD

Hafnium disulfide (HfS2) is expected to surpass MoS2 and WS2 as a two-dimensional (2D) semiconductor, with the added advantage that its native oxide, HfO2, is a widely used high-k dielectric. Unlike MoS2 and WS2, which are generally synthesized by metal-organic chemical vapor deposition (MOCVD) for semiconductor applications, HfS2 has not yet been grown by this method, probably due to a lack of suitable precursors for depositing thin, uniform, and stoichiometric films. Here, we introduce two nitrogen-coordinated hafnium precursors, Hf(TMSAEDMA)(NMe2)3 1 and Hf(TMSAEDMA)(NEtMe)3 2, derived from the functionalized ligand system N-trimethylsilylamino-ethane-N',N'-dimethylamine (TMSAEDMA). Both complexes exhibit adequate volatility and high reactivity toward elemental sulfur, enabling MOCVD under moderate, H2S-free conditions. Using precursor 1, crystalline HfS2 was deposited, confirmed by structural and compositional analyses. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) revealed rapid surface oxidation to HfO2 and HfOxSy, naturally forming heterostructures relevant for transistor applications. For electrical characterization, HfS2 films were directly deposited on interdigitated electrode (IDE) structures. Their conductivity was evaluated both with the native oxide present and after capping with a thin ZnS layer, with both configurations preserving the conductivity. This work establishes the first MOCVD method for high-quality HfS2, identifies 1 as a versatile precursor for chalcogenide growth, and provides detailed insights into oxidation pathways, highlighting the material's potential for next-generation semiconductor devices.