Bias-induced wavelength-selective photoresponse and photoconductivity polarity reversal in Mg-GaN/Ga2O3 heterojunction photodetectors

Here, a bias-tunable dual-mode ultraviolet (UV) photodetector based on p-Mg-GaN/β-Ga2O3 heterojunction is reported. The device mainly responds to UVC (254 nm) under reverse bias and actively switches to UVA (365 nm) response under low forward bias. When the forward bias voltage exceeds ∼2 V, a significant negative photoconductivity (NPC) phenomenon occurs. Under 365 nm illumination, the NPC originates from the instantaneous filling of interface states and the barrier modulation at the heterojunction. In contrast, the mechanism under 254 nm illumination exhibits a strong bias dependence: at 4 V, it is governed by a slow process associated with bulk deep-level states; when the bias increases to 6 V, the dominant process changes to rapid interface barrier modulation. This study reveals the bias-tunable NPC mechanism switching phenomenon in Ga2O3 heterojunctions and provides a new physical basis and material platform for the design of intelligent ultraviolet photodetectors with spectral selectivity and adjustable polarity.