Imaging ultra-weak UV light below 100 pW cm^-2 using a 4H-SiC photodetector with an Al₂O₃ interfacial layer

Weak light detection is crucial in various practical applications such as night vision systems, flame monitoring, and underwater operations. Decreasing the dark current of a photodetector can effectively mitigate noises, consequently enhancing the signal-to-noise ratio and overall weak light detection performance. Herein, we demonstrate a 4H-SiC UV photodetector capable of detecting extremely weak UV light. This device comprises a photosensitive layer of 4H-SiC, two TiN electrodes and an atomically thin Al₂O₃ interfacial layer between TiN and the C surface of 4H-SiC. Under 360 nm UV light illumination, the proposed Al₂O₃ device demonstrates an ultra-low dark current of 18 fA, possibly benefiting from the effective passivation of interfacial carriers, and a boosted photo-to-dark current ratio of 6.7 × 10⁷. Consequently, it achieves a weak-light detection limit as low as 31.8 pW cm^-2, significantly outperforming the control device lacking Al₂O₃. When compared to previously reported SiC photodetectors, our Al₂O₃ device boasts an exceptional large linear dynamic range of 172 dB. Leveraging this, we construct a photodetector array capable of clearly imaging an object under ultra-weak light illumination below the 100 pW cm^-2 level. The proposed photodetector represents a significant advancement in the development of highly sensitive image sensors for weak light detection.