Controllable Synthesis of Out-of-Plane Grown Bi₂TeO₅ with High-κ and Anisotropy for High-Performance Field-Effect Transistors

Two-dimensional (2D) van der Waals (vdW) dielectrics with high-κ and anisotropy are crucial for advanced field-effect transistors (FETs) and other anisotropic electronic devices. Here, we demonstrate a 2D vdW dielectric, Bi₂TeO₅, that uniquely combines high-κ with pronounced anisotropy. By adjusting the precursor mass during chemical vapor deposition, we can controllably synthesize Bi₂TeO₅ with orientations ranging from in-plane to out-of-plane. As a dielectric in MoS₂ top-gate FETs, Bi₂TeO₅ achieves <i>I</i>_on/<i>I</i>_off exceeding 10⁷, a subthreshold swing of 65.2 mV dec^-1, a small hysteresis of 15 mV, and ultralow leakage current density below 10^-5 A cm^-2, attributed to its large effective electron mass (<i>m</i>* = 27.4 <i>m</i>₀). The FET shows stable performance over 1000 cycles. Additionally, Bi₂TeO₅ with in-plane anisotropy induces gate-tunable electrical anisotropic behaviors in monolayer MoS₂ through interface coupling. Our findings introduce a high-performance dielectric for next-generation FETs and demonstrate its potential applications in anisotropic electronics.