Single-crystalline van der Waals layered dielectric with high dielectric constant.

The scaling of silicon-based transistors at sub-ten-nanometre technology nodes faces challenges such as interface imperfection and gate current leakage for an ultrathin silicon channel 1,2 . For next-generation nanoelectronics, high-mobility two-dimensional (2D) layered semiconductors with an atomic thickness and dangling-bond-free surfaces are expected as channel materials to achieve smaller channel sizes, less interfacial scattering and more efficient gate-field penetration 1,2 . However, further progress towards 2D electronics is hindered by factors such as the lack of a high dielectric constant (κ) dielectric with an atomically flat and dangling-bond-free surface 3,4 . Here, we report a facile synthesis of a single-crystalline high-κ (κ of roughly 16.5) van der Waals layered dielectric Bi 2 SeO 5 . The centimetre-scale single crystal of Bi 2 SeO 5 can be efficiently exfoliated to an atomically flat nanosheet as large as 250 × 200 μm 2 and as thin as monolayer. With these Bi 2 SeO 5 nanosheets as dielectric and encapsulation layers, 2D materials such as Bi 2 O 2 Se, MoS 2 and graphene show improved electronic performances. For example, in 2D Bi 2 O 2 Se, the quantum Hall effect is observed and the carrier mobility reaches 470,000 cm 2  V -1  s -1 at 1.8 K. Our finding expands the realm of dielectric and opens up a new possibility for lowering the gate voltage and power consumption in 2D electronics and integrated circuits.