Epitaxial Growth of 2D Ultrathin Metastable γ-Bi 2 O 3 Flakes for High Performance Ultraviolet Photodetection

Ultraviolet detection is of great significance due to its wide applications in the missile tracking, flame detecting, pollution monitoring, and so on. The nonlayered semiconductor γ-Bi2 O3 is a promising candidate toward high-performance UV detection due to the wide bandgap, excellent light sensitivity, environmental stability, nontoxic and elemental abundance properties. However, controllable preparation of ultrathin 2D γ-Bi2 O3 flakes remains a challenge, owing to its nonlayered structure, metastable nature, and other competing phases. Moreover, the UV photodetectors based on 2D γ-Bi2 O3 flake have not been implemented yet. Here, ultrathin (down to 4.8 nm) 2D γ-Bi2 O3 flakes with high crystal quality are obtained via a van der Waals epitaxy method. The as-synthesized single-crystalline γ-Bi2 O3 flakes show a body-centered cubic structure and grown along (111) lattice plane as revealed by experimental observations. More importantly, photodetectors based on the as-synthesized 2D γ-Bi2 O3 flakes exhibit promising UV detection ability, including a responsivity of 64.5 A W-1 , a detectivity of 1.3 × 1013 Jones, and an ultrafast response speed (τrise  ≈ 290 µs and τdecay  ≈ 870 µs) at 365 nm, suggesting its great potential for various optoelectronic applications.