Structural design and performance improvement of flip-chip AlGaInP mini light-emitting diodes

Abstract

Flip-chip (FC) aluminum gallium indium phosphide (AlGaInP) mini light-emitting diodes (mLEDs) with p and n lateral electrode structures and a larger light-emitting area have significant potential for integrating red, green, and blue mLEDs of locally dimmable zones for developing new-generation LED-backlit liquid crystal displays. Herein, an FC AlGaInP mLED having 9 × 6 mil dimensions is fabricated using wafer bonding and transfer technology methods. We propose a patterned n-gallium-arsenide (GaAs) epilayer by etching for ohmic contact and optimizing the specific contact resistance of an FC mLED. The light-output intensity images demonstrated that this etching process improved the uniformity of current distribution and matched the simulation results. Compared with conventional FC mLEDs, the output powers of FC mLEDs with a patterned n-GaAs layer increased from 3.4% to 4.5% and the wall-plug efficiency improved by 1.04%. Moreover, Ag was applied as a reflector on patterned n-GaAs rather than AuGe. The output power of FC mLEDs with an Ag reflector showed a 3.5%–8.2% improvement over FC mLEDs with an AuGe reflector. Finally, FC mLEDs that were encapsulated with epoxy and far-field radiation patterns indicated that packaged FC mLEDs had a smaller divergence angle and narrower viewing angle.