Vertically aligned InGaN nanowire arrays on pyramid textured Si (1 00): A 3D arrayed light trapping structure for photoelectrocatalytic water splitting

•InGaN NWs are grown on pyramid textured Si, forming 3D nano-grating structure.•Enhanced light absorption is due to pyramid-like NW arrays and tilted NWs.•3D nano-grating structured InGaN NWs exhibit 200% enhancement in photocurrent.•FDTD simulations verify light trapping of 3D nano-grating structure.•The inner n-InGaN/n-Si heterostructure fosters photocarrier separation. To boost photoelectrocatalytic water splitting, we synthesize InGaN nanowires (NWs) on pyramid textured Si (100) substrates (InGaN/PSi) by plasma-assisted molecular beam epitaxy which act as a novel anti-reflection 3D nano-grating light trapping structure. An InGaN/PSi photoanode exhibits 200% enhancement of the photocurrent compared to that of InGaN NWs on planar Si (InGaN/Si), which is mainly ascribed to the light trapping effects from pyramid-like NW arrays and the tilt structure of the NW arrays, number of InGaN NWs and better wettability. An ultra-low reflectivity around 1.5% due to the pyramid texture and tilt of the NWs implies enhanced absorption. Finite Difference Time Domain (FDTD) simulations verify the light trapping of the 3D nano-grating structure. Furthermore, the inner n-InGaN/n-Si heterostructure fosters photocarrier separation, driving holes to the surface to enhance water oxidation. This research provides a vital approach, exploiting a novel 3D nano-grating light trapping structure to enhance photoelectrocatalytic water splitting by the combined effects of light management, heterostructure formation, doping, and maximizing surface wetting and surface area, which also has significance in other photoelectrocatalytic fields.