High LightExtraction GaN-Based Vertical LEDs with Double Diffuse Surfaces

employing double diffuse surfaces were fabricated. This novel LED structure includes one top transmitted diffuse surface and another diffuse omnidirectional reflector (ODR) on the bottom of a LED chip. The diffusive ODR consists of a roughened p-type GaN layer, an indium–tin–oxide (ITO) low refractive index layer, and an Al layer. The surface of the p-type GaN-layer was nat-urally roughened while decreasing the growth temperature to 800 C. After flip-bonding onto a Si substrate by AuSn eutectic metal and laser lift-off processes to remove the sapphire substrate, an anisotropic etching by dilute potassium hydroxide (KOH) was employed on the-face n-GaN layer to obtain transmitted diffuse surfaces with hexagonal-cone morphology. The double diffused surfaces LEDs show an enhancement of 56 % and 236% in light output power compared to single side diffused surface and conventional LEDs, respectively. The devices also show a low leakage current in the order of magnitude of 10 8 A at 5 V and a calculated external quantum efficiency of about 40%. The high scattering efficiency of double diffused surfaces could be responsible for the enhancement in the device light output power. Index Terms—Double diffuse surfaces, GaN, light-emitting diodes (LEDs), light-extraction efficiency. I