Improving Emission Uniformity of InGaN/GaN-Based Vertical LEDs by Using Reflective ITO/Ag n-Contact

Abstract

We investigated the effect of Ti/Al and ITO/Ag n-type contacts on the emission uniformity and light output of different chip-size vertical-geometry light-emitting diodes (VLEDs) for vehicle headlamp application. The forward voltage of the Ti/Al-based reference VLEDs decreased from 3.38 to 3.20 V at 1500 mA with increasing chip size from (1280 x 1000 mu m(2)) to (1700 x 1700 mu m(2)), whereas that of the ITO/Ag-based samples changed from 3.37 to 3.15 V. Regardless of chip size, the ITO/Ag-based samples revealed higher light output power than the reference samples. For example, the ITO/Ag-based samples (chip size of 1700 x 1700 mu m(2)) exhibited 3.4% higher light output power at 1500 mA than the reference samples. The ITO/Ag samples underwent less degradation in the Wall-plug efficiency (WPE) than the reference sample. For instance, the ITO/Ag-based samples (1700 x 1700 mu m(2)) gave 4.8% higher WPE at 1500 mA than the reference samples. The ITO/Ag-based samples illustrated more uniform emission than the Ti/Al-based sample. Both the reference and ITO/Ag-based samples underwent no degradation when operated at 1500 mA for 1000 h.