Improvement of surface emission for GaN-based light-emitting diodes with a metal-via-hole structure embedded in a reflector

This work demonstrates the feasibility of gallium nitride (GaN)-based light-emitting diodes (LEDs) with a metal-via-hole structure embedded in a reflector on the backside of sapphire substrate. Luminescence intensity for the surface-emitting LEDs is enhanced by mirroring efficaciously the downward light emitted from the InGaN/GaN multiquantum wells (MQWs) owing to the deep ladder-shaped inclined reflector on the backside of substrate. A metal-via-hole structure with a deep ladder shape was also processed with a wet-etching method at a high temperature to pattern the sapphire substrate deeply. The electroplating method was used to fill the area of patterned sapphire substrate with copper subsequently to produce a heat spreader path through the metal-via-hole and to strengthen the sapphire substrate with the void structure. Experimental results indicate that the GaN-based surface-emitting LEDs with a reflector for the planar, deep ladder-shaped sapphire, and metal-via-hole structures exhibit a luminescence intensity of 37%, 178%, and 226%, respectively, which are higher than the conventional ones under an injection current of 20 mA. A more stable peak wavelength shift is also observed for the metal-via-hole LED structure.