Controlled formation of GaN nanostructures through contactless photoelectrochemical etching for supercapacitor electrode applications

Nanostructured n-type GaN layers were fabricated using the Contactless photoelectrochemical (PEC) etching method in KOH-based solutions under ultraviolet illumination. By adjusting the KOH concentration, distinct surface morphologies were obtained. Low-concentration KOH solutions led to the formation of nanorods at dislocation sites, whereas high-concentration solutions induced interconnected etch pits. Cathodoluminescence (CL) analysis confirmed a strong correlation between the resulting nanostructures and dislocation sites. The formation mechanisms of different nanostructures were discussed. Electrochemical characterization revealed significantly enhanced performance in etched GaN samples. In particular, the GaN layer treated with 0.02 M KOH and 0.02 M K₂S₂O₈ exhibited a 16-fold increase in specific capacitance compared to the pristine GaN layer.