A New Synthetic Method for HfS₂ 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 HfO_xS_y, 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.