Large‐Scale Ultrathin 2D Wide‐Bandgap BiOBr Nanoflakes for Gate‐Controlled Deep‐Ultraviolet Phototransistors

Abstract

Ternary two-dimensional (2D) semiconductors with controllable wide bandgap, high ultraviolet (UV) absorption coefficient, and critical tuning freedom degree of stoichiometry variation have a great application prospect for UV detection. However, as-reported ternary 2D semiconductors often possess a bandgap below 3.0 eV, which must be further enlarged to achieve comprehensively improved UV, especially deep-UV (DUV), detection capacity. Herein, sub-one-unit-cell 2D monolayer BiOBr nanoflakes (≈0.57 nm) with a large size of 70 µm are synthesized for high-performance DUV detection due to the large bandgap of 3.69 eV. Phototransistors based on the 2D ultrathin BiOBr nanoflakes deliver remarkable DUV detection performance including ultrahigh photoresponsivity (R_λ , 12739.13 A W^-1 ), ultrahigh external quantum efficiency (EQE, 6.46 × 10⁶ %), and excellent detectivity (D*, 8.37 × 10¹² Jones) at 245 nm with a gate voltage (V_g ) of 35 V attributed to the photogating effects. The ultrafast response (τ_rise = 102 µs) can be achieved by utilizing photoconduction effects at V_g of -40 V. The combination of photocurrent generation mechanisms for BiOBr-based phototransistors controlled by V_g can pave a way for designing novel 2D optoelectronic materials to achieve optimal device performance.