Reduced efficiency droop of nonpolar a-plane (11-20) GaN-based light-emitting diodes by vertical injection geometry

Vertical nonpolar a-plane (11-20) InGaN/GaN light-emitting diodes (LEDs) have been demonstrated by using laser lift-off technique. The forward voltage of the a-plane vertical LEDs was 4.3 V at 350 mA, which was reduced by 0.8 V compared to that of the a-plane lateral LEDs. The vertical geometry of the a-plane LEDs produced the higher quantum efficiency with a low efficiency droop and also enhanced the output power by more than 40%, when compared to those of a-plane lateral LEDs. These results can be attributed to the high thermal dissipation as well as uniform current spreading of the vertical geometry of the a-plane LEDs. Furthermore, elimination of the highly defected GaN nucleation layer after removing the sapphire substrates during the fabrication process can also enhance current injection efficiency, followed by the increase in the output power.