Innovative FTO/C ₃ N ₄ Photoconductive Architecture for Ultraviolet - Visible Photodetection

The performance of photodetectors based on two-dimensional graphitic carbon nitride (g-C 3 N 4 ) is often limited by the poor morphology of the semiconductor films, which are typically porous and inhomogeneous. Here, we report that controlling the annealing kinetics is crucial for fabricating high-quality, compact g-C 3 N 4 thin films. By gradually reducing the heating rate to 1 °C per minute during the thermal deposition of g-C 3 N 4 on patterned fluorine-doped tin oxide (FTO) electrodes, we achieve a distinct morphological transition from aggregated bulk material to a uniform, dense film. This structural optimization enables the construction of a metal–semiconductor–metal photodetector that exhibits a pronounced response across the ultraviolet–visible spectrum. The device shows a responsivity of 2.5 milliamperes per watt at 410 nanometres and a high photo-to-dark current ratio of approximately 40 under a low bias of 1 volt. The enhanced performance originates from the formation of an ohmic contact at the FTO/g-C 3 N 4 interface and the compact film structure that facilitates efficient carrier transport. Our findings highlight annealing rate control as a key parameter for film quality and present a viable route to high-performance pure-phase g-C 3 N 4 photodetectors.