Subsurface GaN porous structure (PS) of tens nm in pore cross-sectional dimension can be fabricated through an electrochemical etching (ECE) process in a high-conductivity GaN layer, which can be implemented by heavy Si doping. Techniques have been developed for inserting colloidal quantum dots (QDs) into such a PS. We have shown that the QD emission efficiency and Förster resonance energy transfer can be significantly enhanced in such a nanoscale cavity. Also, such a PS can shield the compressive strain in a GaN template caused by the sapphire substrate and relax the strain in the overgrown AlGaN or InGaN/GaN quantum well layers. Such a strain relaxation mechanism can reduce the quantum-confined Stark effect and change the band structure of the overgrown InGaN/GaN quantum wells for enhancing their emission efficiency. Meanwhile, the ECE technique can be upgraded for implementing a mesa array of color filter by mixing QDs with ECE electrolyte，which is a simple and potential method in the fabrication of multiple-color filters for display application. At this presentation, these three PS application subjects will be discussed.