Vertically Graded Oxygen Vacancies in Amorphous Ga₂O₃ for Offsetting the Conventional Trade-Off between Photoresponse and Response Time in Solar-Blind Photodetectors

Recently, amorphous Ga 2 O 3 -based photodetectors are garnering interest for their relative ease-of-growth at room temperature and their virtuous use in flexible electronics. However, a major concern that remains is the huge trade-off between key performance parameters, viz., photoresponse and response time. Being replete with oxygen vacancies, acting as trap centers, devices usually boast a large photoresponse but at the cost of longer response time due to prolonged carrier recombination. Most of remedial measures to offset this trade-off include oxygen vacancy engineering but in a continuous manner, implying creating/deleting vacancies throughout the film thickness, leading to a change in only one of the parameters. Herein, we propose defect engineering in amorphous Ga 2 O 3 by grading oxygen vacancies using an intermittent oxygen supply. XPS depth profile studies confirm gradation of vacancies, which may be accessed by applying a different bias, in resonance with electric field distribution simulations. Graded vacancy films show negligible persistent photoconductivity, a high PDCR of 3 × 10 3, a high UV–vis rejection ratio of 1.49 × 10 4, and a fast fall time of 85 ms as opposed to continuous supply films, which show either high photoresponse or fast speed (in seconds). This work provides a way to use graded oxygen vacancies as tool in defect engineering to offset the trade-off and achieve high photoresponse and fast response time in amorphous Ga 2 O 3 films simultaneously.