Wet Etching of GaN-Based Optoelectronics From Fundamental Mechanisms to Advanced Device Integration

GaN-based optoelectronics face persistent challenges, particularly the low light extraction efficiency, which primarily arises from the high refractive index of GaN. This property results in significant internal light reflection at the GaN/air interface, thereby limiting device performance. To mitigate this issue, porous GaN has emerged as a promising solution due to its ability to modify optical properties at the micro- and nanoscale. This paper presents a comprehensive review of wet etching techniques employed for fabricating porous GaN structures, including electrochemical etching, photoelectrochemical etching, and defect-selective etching methods. These approaches are vital for achieving tunable porosity, structural uniformity, and precise control over morphology, which are critical for optimizing device integration and functionality. Furthermore, the mechanisms by which porous GaN enhances light extraction are systematically analyzed. These include refractive index modulation, enhanced light scattering, increased critical angle for total internal reflection, and improved reflectivity through the incorporation of distributed Bragg reflector (DBR) effects. These mechanisms collectively contribute to better out-coupling of generated photons.In addition, the wide-ranging applications of porous GaN are explored, covering ultraviolet light-emitting diodes (UV LEDs), full-color micro-LED displays, high-sensitivity ultraviolet photodetectors, and advanced optical devices such as photonic crystals and optical resonators. Despite its benefits, challenges remain, including the need to fully understand how porous architecture parameters affect device reliability and long-term performance. Future research should emphasize integrated material-structure design strategies and broaden the scope of application in next-generation optoelectronic technologies.