Performance enhancement of GaN-based near-ultraviolet flip-chip light-emitting diodes with two-step insulating layer scheme on patterned sapphire substrate

Nitride-based near-ultraviolet (NUV) flip-chip (FC) light-emitting diodes (LEDs) on patterned sapphire substrate (PSS) with n-contact full-via-holes (FVH) structure have been fabricated by a two-step insulating layer (IL) method. Comparing with the conventional one-step IL method, the NUV FCLEDs manufactured by two-step IL method exhibit a reduction of 0.19 V in forward voltage and an enhancement of 36.2% in the wall-plug efficiency (WPE). In addition, the WPE of two-step IL NUV FCLEDs was enhanced by 108% as compared to that of the one-step IL FCLEDs on flat sapphire substrate. The current density distribution simulation shows a low current density and uniform distribution for the FCLEDs with FVH structure. The enhanced performance could be attributed to the PSS extraction structure and the more uniform current distribution at the active region due to the uniformly distributed via-holes. The results indicate that the proposed two-step IL method is an effective way to achieve high-power and high-efficiency FCLEDs.