Improved Leakage and Output Characteristics of Pixelated LED Array for Headlight application

We investigated the effects of etching conditions on the performance of light-emitting diodes (LEDs) of various sizes aimed at vehicle headlamp applications. Photoluminescence (PL) images showed that after wet etching, the percentage of bad LED arrays significantly increased from 75% to 94%, and the leakage current at -5 V significantly increased from 1.14 10^-9 A to 5.02 10^-6 A. It was shown that plasma etching turned an Ag layer into Ag particles, the size and density of which depended on the treatment time and Ag layer thickness. These Ag particles served as micro-masks during dry etching. Plasma etching produced relatively uniform hillocks of diameters 0.9-1.43 μm and heights 0.85-2.5 μm. Moreover, the PL images showed that dry etching did not degrade the LED arrays. Furthermore, the light output power of the dry-etched LEDs was higher than that of the wet-etched LEDs. For example, the output power levels of the dry-etched LEDs (chip sizes: 240 290 μm², 240 490 μm², and 490 1190 μm²) at 100 mA were 20.4%, 15.0%, and 11.2% higher than those of the corresponding wet-etched LEDs, respectively. Moreover, we demonstrated a vehicle headlamp unit consisting of Ag-particle-based plasma-etched LEDs.