Transition of photoconductive and photovoltaic operation modes in amorphous Ga₂O₃-based solar-blind detectors tuned by oxygen vacancies

We report on the transition of photovoltaic and photoconductive operation modes of the amorphous Ga₂O₃-based solar-blind photodetectors in metal-semiconductor-metal (MSM) configurations. The conversion from Ohmic to Schottky contacts at Ti/Ga₂O₃ interface is realized by tuning the conductivity of amorphous Ga₂O₃ films with delicate control of oxygen flux in the sputtering process. The abundant donor-like oxygen vacancies distributed near the Ti/Ga₂O₃ interface fascinate the tunneling process across the barrier and result in the formation of Ohmic contacts. As a consequence, the serious sub-gap absorption and persistent photoconductivity (PPC) effect degrades the performance of the photoconductive detectors. In contrast, the photovoltaic device with a Schottky contact exhibits an ultra-low dark current less than 1 pA, a high detectivity of 9.82×10¹² cm·Hz^1/2·W^-1, a fast response time of 243.9 μs, and a high ultraviolet C (UVC)-to-ultraviolet A (UVA) rejection ratio of 10³. The promoting performance is attributed primarily to the reduction of the sub-gap states and the resultant suppression of PPC effect. With simple architecture, low fabrication cost, and easy fusion with modern high-speed integrated circuitry, these results provide a cost-effective way to realize high performance solar-blind photodetectors towards versatile practical applications.