Enhanced Light Extraction Efficiency of GaN-Based LEDs With 3-D Colloidal-Photonic-Crystal Bottom Reflector

In this letter, self-assembled polystyrene nano-spheres with a diameter of 193 nm were used to fabricate the 3-D colloidal-photonic-crystal (CPC) bottom reflector for blue GaN-based light-emitting diodes (LEDs). Experimentally, the key point is the hydrophilic treatment of substrate and immediately to disperse the suspension into the substrate at 30 degrees C. The equilibrium between the particle transport and crystallization in the aqueous solution helps CPCs to form a faced-centered-cubic phase when the solution temperature decreases. This will lead to the improvement of reflectivity due to reduced defects, such as dislocations and vacancies, in the CPCs. The light output intensity of the LEDs fabricated with a well-controlled 3-D-CPC bottom reflector increases by 219% compared to that of conventional LEDs without it.