Enhanced Performance of GaN-Based Thin-Film Flip-Chip LEDs With Reflective n-Electrode Insulating Layers

GaN-based thin-film flip-chip LEDs (TFFC-LEDs) are extensively applied in automotive lighting, especially in headlamp applications. However, photon absorption by the n-electrode metal and the limited reflectivity of the bottom reflector in TFFC-LEDs restrict further advancements in optical performance. To address these challenges, we designed and fabricated TFFC-LEDs with reflective n-electrode insulating layers positioned beneath the metal reflector. The n-electrode insulating layer consists of a distributed Bragg reflector (DBR). At an injection current of 10 A, TFFC-LEDs with reflective n-electrode insulating layers exhibited an 8.38% increase in light output power (LOP) and a 7.89% improvement in external quantum efficiency (EQE) compared to TFFC-LEDs without reflective n-electrode insulating layers. Thermal resistance-capacitance characteristics and surface temperature measurements indicate that the reflective n-electrode insulating layers have no adverse impact on the thermal performance of TFFC-LEDs. Furthermore, simulations with TracePro and TFCalc demonstrate that reflective insulating layers can effectively enhance the light extraction efficiency (LEE) of TFFC-LEDs. We believe that reflective n-electrode insulating layers will offer valuable insights for fabricating high-power LEDs, particularly in headlamps.