First-principles insights into Bi₂XO₅ (X = Se, Te) monolayers as high-k gate dielectrics for 2D electronics

Scaling silicon-based transistors to sub-ten-nanometer technology nodes presents significant challenges due to the difficult in achieving both atomic-scale thickness and excellent tunneling performance simultaneously. In this work, we employed first-principles calculations to investigate the dielectric properties of two recently reported van der Waals layered materials, Bi₂SeO₅ and Bi₂TeO₅. Our results reveal that Bi₂SeO₅ and Bi₂TeO₅ monolayers exhibit out-of-plane dielectric constant of 15.2 and 7.6, respectively, with in-plane dielectric constant reaching as high as 39.0 and 26.0. To evaluate their potential as gate dielectrics, we calculated the band offsets and equivalent oxide thicknesses (EOTs) of Bi₂SeO₅ and Bi₂TeO₅ monolayers. The results show that both materials exhibit favorable band offsets relative to silicon and transition-metal dichalcogenide channel materials, along with low EOT. Finally, we estimated the dielectric leakage current density utilizing Bi₂SeO₅ and Bi₂TeO₅ based on a p-doped silicon-channel transistor, predicting a low leakage current (<10⁻⁸ A cm⁻²). Our study provides theoretical insights into the potential application of bismuth selenite and bismuth tellurite monolayers as gate dielectrics in two-dimensional electronics.