Improvement of light extraction efficiency of flip-chip light-emitting diode by texturing the bottom side surface of sapphire substrate

A high light-extraction efficiency was demonstrated in the flip-chip light-emitting diode (FCLED) with a textured sapphire substrate. The bottom side of a sapphire substrate was patterned using a dry etching process to increase the light-extraction efficiency. Light output power measurements indicated that the scattering of photons emitted in the active layer was considerably enhanced at the texturcd sapphire substrate resulting in an increase in the probability of escaping from the FCLED. The light-output power of the FCLED was increased by 40.2% for a 0.4-μm deep FCLED with a periodic distance of 13-μm mesh-type texture on the bottom side of the sapphire substrate.