Fabrication and characterization of high-quality factor GaN-based resonant-cavity blue light-emitting diodes

High-quality factor (Q>1700) GaN-based blue resonant-cavity light-emitting diodes (RCLEDs) incorporating an InGaN/GaN multiquantum well active region, two high-reflectivity dielectric-distributed Bragg reflectors, and a thin indium tin oxide (ITO) layer are fabricated by a two-step substrate transfer technique. Electroluminescence measurements showed a narrow linewidth of 0.26 nm at the wavelength of 450.6 nm by precisely placing the ITO layer at the node position of the electric field, corresponding to a high Q-value of 1720. Further, adopting a chemical-mechanical polishing (CMP) technique to polish the GaN surface after the removal of sapphire substrate, an even higher Q-value of 2170 was obtained. This improvement was attributed to the exclusion of the defect-rich buffer layer and the achievement of a smooth surface with a root mean square roughness below 1 nm. The integrated electroluminescence intensity was enhanced by 40% as compared with the RCLEDs without CMP at a current density of 8 kA/cm ².