Wavelength-selective bipolar photoresponse in CVD-grown β-Bi₂O₃ flakes for multi-logic functionality

With the increasing demand for high-speed and energy-efficient information processing, optoelectronic logic devices are emerging as promising candidates for next-generation in-sensor and wavelength-encoded computing systems. In this work, the growth of β-Bi₂O₃via chemical vapor deposition (CVD) has been achieved by systematically tuning the growth parameters. The β-Bi₂O₃ photodetector devices show a positive photoconductive effect with above-bandgap illumination, while a distinct negative photoconductive effect at longer wavelengths (well below the bandgap) was observed. This bipolar behavior is governed by the competition among photogenerated carrier generation, oxygen vacancy-mediated defect-state dynamics, and electron-phonon scattering-induced mobility reduction. The coexistence of positive and negative photoresponses within the same β-Bi₂O₃ system, modulated by the excitation wavelength, highlights the interplay among photon energy, defect states, electron-phonon interaction, and lattice anharmonicity. By harnessing the coexistence of positive and negative photoconductive effects within a single device and solely modulating the illumination wavelength, we realize all seven fundamental logic gates without changing the device geometry or electrical biasing. This work establishes a compact and reconfigurable approach for wavelength-controlled optoelectronic logic operations, offering a viable pathway toward oxide-based in-sensor computing and multifunctional photonic logic systems.