Output power enhancement of GaN light emitting diodes with p-type ZnO hole injection layer

We report an enhancement of the optical output power of GaN light emitting diodes (LEDs) by addition of a p-type ZnO layer located in close proximity to the active layer (ZnO/GaN LEDs). Arsenic (As)-doped p-ZnO was used as a hole-injecting layer to overcome the drop in external quantum efficiency of GaN LEDs at high drive currents-the so-called "efficiency droop." The output power in ZnO/GaN LEDs was improved up to 40%. This result is useful for development of highly efficient GaN LEDs operating at high current densities that will play a critical role in replacement of incandescent lamps by high efficiency solid-state light bulbs.