Demonstration of high-efficient InGaN-based violet light-emitting diodes with an external-quantum efficiency of more than 40%

High-power InGaN-based violet light-emitting diodes (LEDs), which were fabricated on patterned-sapphire substrate (PSS), have been realized. In order to improve the extraction efficiency in the LEDs, the PSS configuration was optimized by means of photoluminescence (PL). With increasing depth of grooves (D g ) in the PSS, the interference fringes observed in the PL spectrum declined and almost disappeared at D g = 1 μm. The PL and electroluminescence (EL) intensities also increased with increasing D g . These results indicated that the contribution of optical loss resulting from multiplex reflection decreased with increasing D g , and the extraction efficiency was also improved. When the LEDs on the optimized PSS were operated at 20 mA, the wavelength, the output power and the external-quantum efficiency were estimated to be 403 nm, 26.2 mW and 43%, respectively.