Fabrication of GaN Nanostructures by Nanosphere Lithography and Their Enhanced Water-Splitting Property

In this work, polystyrene (PS) microspheres were employed as an etching mask to fabricate nanostructured gallium nitride (GaN) via inductively coupled plasma (ICP) etching. By precise control of the etching process, well-defined nanocylinders and nanopyramids with distinct dimensions were obtained, with the exposed crystal facets varying from (10–10) for nanocylinders to (11–2–1) and (20–2–1) for larger and smaller nanopyramids, respectively. The photoelectrochemical (PEC) performance of these nanostructures was systematically evaluated and compared to planar GaN. All nanostructured samples exhibited significantly enhanced photocurrent densities, with the nanocylinders achieving a maximum saturated photocurrent of 0.31 mA/cm2, approximately 3.1 times higher than planar GaN (0.075 mA/cm2). This enhancement is attributed to the enlarged specific surface area, which improves light absorption and increases the interfacial contact with the electrolyte as well as to the formation of surface states that induce band bending and facilitate more efficient separation and transport of photogenerated carriers. These results demonstrate a scalable, low-cost strategy to improve GaN-based PEC water-splitting performance and provide valuable insights for optimizing nanostructured photoelectrode design.