Investigating the impact of substrate defects on Ga₂O₃/GaN-based ultraviolet photodetector by designing a common-connected electrode

Ga₂O₃/GaN hybrid ultraviolet (UV) photodetector (PD) has photon-carriers generated in the Ga₂O₃ region and transported in the GaN layer. In this work, by designing Ga₂O₃/GaN UV PD with a gate metal on the Ga₂O₃ surface, common-connected with the cathode on the GaN layer, we have revealed that the impact of substrate defects in the GaN region on the photo-generated carrier transport is significant for Ga₂O₃/GaN UV PD. As a result, we have observed asymmetric current in terms of the anode bias of different polarities. According to our measurement, the photocurrent of 8.81 × 10^-5 A/cm²/2.34 × 10^-5 A/cm², the responsivity of 6.65 A/W/1.16 A/W, the rise time of 1.07 s/1.14 s, and the fall time of 1.16 s/1.35 s are achieved at the anode bias of -6 V/+6 V, respectively. When the anode is biased positively, the poorer performances are well attributed to the substrate defects, such that Ga₂O₃/GaN UV PD pushes the photo-generated carriers deep into the more defected GaN substrate region. This observation is further proven by the developed physical models.