Optimization of Light Extraction Efficiency of III-Nitride LEDs With Self-Assembled Colloidal-Based Microlenses

Improvement of light extraction efficiency of InGaN LEDs using colloidal-based SiO
₂
/polystyrene (PS) microlens arrays was demonstrated. The size effect of the SiO
₂
microspheres and the thickness effect of the PS layer on the light extraction efficiency of III-nitride LEDs were studied. The monolayer rapid convective deposition conditions for SiO
₂
microspheres were also investigated. Ray tracing simulations show that the use of microlens arrays can lead to increase in light extraction efficiency of InGaN LEDs by 2.64 times. This is consistent with experiments that demonstrated 2.49 times improvement in light extraction utilizing SiO
₂
/PS microlens arrays. The enhancement in light extraction efficiency is attributed to increase in effective photon escape cone due to SiO
₂
/PS microlens arrays, and reduced Fresnel reflection within the photon escape cone due to the grading of refractive index change between GaN/SiO
₂
/PS/air interface.