Quantitative insight into illumination-induced barrier lowering mediated by self-trapped-holes in Ga2O3 Schottky photodiodes

Anomalously high photoresponsivity exceeding the theoretical photovoltaic limit has been widely reported in Ga2O3 Schottky barrier photodiodes (SBPDs) but seldom observed in heterojunction photodiodes (HJPDs). Here, we quantitatively identify the illumination-induced Schottky barrier lowering (SBL) effect mediated by self-trapped holes (STHs) as the physical origin of this discrepancy. Bias-dependent photoresponse spectra, photocurrent transients, and Franz–Keldysh effect-based rigorous modeling reveal that an apparent photoresponsivity of 19.8 A/W and a corresponding external quantum efficiency (EQE) of 95.8 in β-Ga2O3 SBPD are results of a 0.22 eV reduction of the Schottky barrier under solar-blind illumination. The STH-mediated SBL facilitates electron injection under reverse bias, yielding EQE values far beyond the unity photovoltaic limit. In comparison, NiO/β-Ga2O3 HJPDs with type-II band alignment enable efficient extraction of photogenerated carriers and exhibit intrinsic photoresponse behavior. The model quantitatively elucidates the mechanism of STH-mediated photoresponse gain, offering physical insights for engineering ultrawide-bandgap photodetectors.