Ferroelectric Bi ₂ O ₃ Nanoflakes for a High Polarization Ratio in UVC Photodetectors

Low-dimensional ferroelectrics with wide bandgaps demonstrate great potential in realizing high-contrast polarimetric ultraviolet-C (UVC) photodetectors. However, numerous UVC platforms suffer from limited polarization discrimination, and their polar-order signatures may diminish at elevated temperatures, thereby hindering robust polarimetric readout. Here, we report rhombohedral ferroelectric Bi 2 O 3 nanoflakes synthesized via a pressure-induced flux-assisted growth method, with a noncentrosymmetric second-harmonic generation (SHG) response observed up to ∼750 K. Cross-sectional low-loss electron energy-loss spectroscopy (EELS) yields an optical bandgap of 3.96 eV, and wavelength-dependent photoresponse measurements show a pronounced UVC response with strongly suppressed response at longer wavelengths, supporting solar-blind operation. Poling-dependent photovoltaic I – V switching and bias-tunable polarization-resolved SHG collectively indicate a correlation between the enhanced photocurrent and the switchable polar state, consistent with the bias-tunable SHG symmetry response. Consequently, an electrically tunable polarization ratio is achieved. Planar Au/Bi 2 O 3 /Au photodetectors exhibit polarization-resolved UVC photoresponse at 265 nm with a polarization ratio up to 42.7 and reversible photocurrent polarity upon reversing the poling direction, allowing a switchable sign of the polarization-dependent photoresponse. These results highlight Bi 2 O 3 nanoflakes as a wide-bandgap polar platform for electrically tunable polarization-sensitive UVC optoelectronics.