The Fabrication of BiVO₄/WO₃/GaN Heterojunction and its Enhanced Water Splitting Performance

Abstract GaN has garnered significant attention for water splitting due to its excellent light absorption, carrier transport properties, and chemical inertness. However, its bandgap of 3.4 eV restricts absorption to the ultraviolet range. To address this limitation, narrow-bandgap semiconductors BiVO 4 and WO 3 were deposited on the GaN surface using the sol-gel method. Photoelectrochemical water-splitting tests revealed that the saturated photocurrent densities of GaN/BiVO 4 and GaN/BiVO 4 /WO 3 under full-spectrum illumination were 1.42 and 1.86 times greater than that of GaN alone, respectively. This improvement is attributed to the smaller bandgaps of BiVO 4 and WO 3 , which significantly extend the spectral absorption range of GaN. Additionally, BiVO 4 and WO 3 form heterojunctions through energy alignment, and the built-in electric field at the heterojunctions accelerates the separation of photo-generated carriers, further enhancing energy conversion efficiency. The study also found that the BiVO 4 and WO 3 films exhibit a 2D flake morphology, providing larger surface areas that enhance light absorption and carrier transport, thereby improving water-splitting efficiency. Our research paves a new path for the application of GaN in water splitting.