Advances in fabrication techniques for porous GaN: a review of methods and applications

Gallium nitride (GaN) is recognized for its exceptional material properties that support the design of both high-efficiency optoelectronic and high-performance power devices. Yet, its widespread application still faces bottlenecks, including poor light extraction due to total internal reflection, strain accumulation from lattice and thermal mismatches, and defect-induced performance degradation. The porosity structures within GaN can tackle these challenges by enhancing light out-coupling, accommodating strain relaxation during epitaxial growth, and providing quantum confinement and improved thermal management. This review discusses the advances in wet etching methods, particularly electrochemical (EC), metal-assisted chemical etching (MacEtch), and photoelectrochemical (PEC) etching for tailoring porous GaN morphologies. The intricate interplay between doping levels, applied bias, electrolyte concentration, and illumination conditions is analyzed to clarify their effects on pore size distribution, uniformity, and resultant optical behavior. A significant contribution of this work is the proposal of a systematic, morphology-specific framework that optimizes PEC etching parameters for achieving targeted porous structures, addressing the lack of standardized protocols across studies. In addition, this paper highlights unresolved challenges such as unintended porosity, surface oxidation, and post-etch contamination, and summarizes mitigation strategies reported to date. By positioning these insights within the broader context of emerging applications, including advanced light emitters, sensors, energy devices, and biointerfaces, this review underscores the versatile potential of porous GaN when fabricated under controlled, well-optimized conditions. Ultimately, this work intends to guide future efforts toward more reliable, scalable, and application-specific porous GaN technologies that can better leverage the unique advantages of this material platform for next-generation photonic and nanoelectronics systems.