Deciphering the photocurrent polarity of Bi2O2Se heterojunction phototransistors to enhance detection performance

Abstract

With the emergence of bismuth-based oxychalcogenide materials, Bi₂O₂Se shows superiority in photodetection owing to its favorable mobility and air stability. Nevertheless, the photodetection performance is limited by its low bandgap and extinction coefficient in the near-infrared region. Here, by stacking C₆₀/Bi₂O₂Se heterojunction onto graphene with a symmetrical electrode, we observed distinctive polarity variation in the broadband photocurrents (488–1550 nm) owing to the wavelength-dependent band alignment. Meanwhile, the all-negative polarity responses of graphene/Bi₂O₂Se demonstrate high photo-responsivity (∼7160 A W⁻¹) with 1.7 × 10⁶% external quantum efficiency, fast speed down to 57 μs and detectivity up to 6.96 × 10¹⁰ Jones, which are superior compared with previous work. A higher photo-responsivity (∼170 A W⁻¹) communication band (1310 and 1550 nm) is realized for graphene/C₆₀/Bi₂O₂Se than for previous related work. The coupling energy bands of Bi₂O₂Se and C₆₀ were determined by first-principles calculation, suggesting two carrier transfer paths into the graphene channel (charge separation and tunneling injection). This was further verified by gate modulation and a control group. This unique photo-response phenomenon and high-performance phototransistor will enable next-generation large-scale array optical imaging and provide a valid platform for exploring communication band applications and polarity converting of photocurrents.