Controllable preparation of ultrathin 2D BiOBr crystals for high-performance ultraviolet photodetector

Ternary layered compound materials (bismuth oxyhalides and metal phosphorus trichalcogenides) stand out in electronic and optoelectronic fields due to their interesting physical properties. However, few studies focus on the preparation of high-quality two-dimensional (2D) BiOBr crystals with a typical layered structure, let alone their optoelectronic applications. Here, for the first time, high-quality 2D BiOBr crystals with ultrathin thicknesses (less than 10 nm) and large domain sizes (∼100 µm) were efficiently prepared via a modified space-confined chemical vapor deposition (SCCVD) method. It is demonstrated that a moderate amount of H₂O molecules in the SCCVD system greatly promote the formation of high-quality 2D BiOBr crystals because of the strong polarity of H₂O molecules. In addition, a linear relationship between the thickness of BiOBr nanosheets and Raman shift of A1g(1) mode was found. Corresponding theoretical calculations were carried out to verify the experimental data. Furthermore, the BiOBr-based photodetector was fabricated, exhibiting excellent performances with a responsivity of 12.4 A W⁻¹ and a detectivity of 1.6×10¹³ Jones at 365 nm. This study paves the way for controllable preparation of high quality 2D BiOBr crystals and implies intriguing opportunities of them in op toelectronic applications.