Comparative Study of Highly Reflective ITO/DBR and Ni/Ag ohmic Contacts for GaN-Based Flip-Chip Light-Emitting Diodes

Heat removal and current spreading uniformity are important for the realization of highly efficient light-emitting diodes (LEDs). Here we have compared two types of GaN-based flip-chip LEDs (FCLEDs) with highly reflective indium-tin oxide (ITO)/distributed Bragg reflector (DBR) and Ni/Ag p-type ohmic contacts. The via-based n-type contact structure was implemented to increase the utilization ratio of active region area and improve current spreading over the entire LEDs. Compared with FCLED with Ni/Ag, the FCLED with ITO/DBR shows a 6.3% higher light output power (LOP) at low current density of 31 A/cm2 (90 mA) due to higher reflectance of ITO/DBR ohmic contact. However, at high injection currents, the Ni/Ag ohmic contact in FCLED alleviates self-heating issue by means of its superior heat dissipation performance. We also found that the less area coverage between ITO and metallization layer have a negative influence on heat dissipation performance of FCLED with ITO/DBR. As a result, the maximum light output power (LOP) of the FCLED with Ni/Ag obtained at 292.8 A/cm2 is 1.3 times larger than that of FCLED with ITO/DBR obtained at 196.3 A/cm2.