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. were elucidated. 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 K 2 S 2 O 8 exhibited a 16-fold increase in specific capacitance compared to the pristine GaN layer. • Achieved concentration-dependent selective etching: Low KOH formed nanorods at dislocations; high KOH created etching pits via dislocation-targeted dissolution. • Enhanced optical properties: GaN nanorod arrays showed intensified band-edge PL emission, indicating superior optoelectronic quality. • Stress relaxation confirmed: Raman spectroscopy analysis of GaN nanorod arrays and GaN etch pits demonstrated effective lattice strain reduction. • Record electrochemical performance: 16 times higher specific capacitance and 100% capacitance retention over 5000 cycles, showcasing ultra-stable energy storage. • Versatile supercapacitor potential: The tailored nanostructures of GaN nanorod arrays provide a promising platform for high-efficiency, durable electrode materials.