In recent years, rare-earth oxyhalides and transition-metal nitride halides have been reported as gate dielectrics in field-effect transistor (FET) applications. However, chalcogenide halides have been rarely explored as gate dielectrics. In this work, we systematically evaluated the potential of $\mathrm{Sc}XY$ ($X$ = $\mathrm{S},\mathrm{Se},\mathrm{Te}$; $Y$ = $\mathrm{Cl},\mathrm{Br},\mathrm{I}$) monolayers as replacements for hBN, focusing on their stability, electronic properties, dielectric properties, and leakage current through first-principles calculations. Based on analyses of stability and band gap, we identified five monolayers, namely $\mathrm{Sc}\mathrm{S}Y$ ($Y$ = $\mathrm{Cl},\mathrm{Br},\mathrm{I}$), $\mathrm{Sc}\mathrm{Se}\mathrm{Br}$, and $\mathrm{Sc}\mathrm{Se}\mathrm{I}$, which are easily exfoliable and exhibit both thermodynamic and dynamic stability, with large band gaps (>2.0 eV). These materials also exhibit favorable band offsets, high dielectric constants (${\epsilon }_{\parallel }^0\sim 14.36-18.54$ and ${\epsilon }_{\mathrm{\perp }}^0\sim 3.25-4.35$), high breakdown strength (0.99 – 1.54 MV/cm), and low leakage currents (<${10}^{-6}$ A ${\mathrm{cm}}^{-2}$), indicating their potential as gate dielectric materials. Notably, the $\mathrm{Sc}\mathrm{SBr}$ monolayer stands out as the most promising candidate among the five ScXY monolayers, owing to its highest breakdown strength (1.54 MV/cm), largest conduction band minimum (CBM) offset, and the lowest leakage current (<${10}^{-10}$ A ${\mathrm{cm}}^{-2}$). Our study offers valuable insights into the development of chalcogenide halide gate dielectrics for next-generation electronic devices.

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• Dielectric properties
• 2-dimensional systems
• Chalcogenides
• Dielectrics
• Field-effect transistors
• Layered crystals
• Metal halides
• Density functional calculations