Using Self-Aligned Si Barrier to Enhance the Contrast Ratio and Performance of Pixelated Light Emitting Diode for Vehicle Headlamp

We investigate the effects of pixel distance and light emitting diode (LED) thickness on the luminance distribution and contrast ratio of a 16 × 16 blue and white LED array for vehicle headlamp application. With increasing pixel distance from 10 to 20 μm, the contrast ratio increased from 33:1 to 51:1 for white LEDs and from 37:1 to 48:1 for blue LEDs. As the LED thickness decreased from 4.5 to 2.0 μm, the contrast ratio increased from 37:1 to 62:1 for blue LEDs and from 33:1 to 97:1 for white LEDs. The blue LEDs fabricated with ultrathin-GaN and self-aligned Si barrier showed the contrast ratio of 48:1 and 39:1, respectively, while the white LEDs with ultrathin-GaN and self-aligned Si barrier yielded the contrast ratio of and 89:1 and 99:1. Further, LEDs with the self-aligned Si barrier had better luminance uniformity than those with the ultrathin-GaN. LED array with the self-aligned Si barrier exhibited narrower dark space than that with the ultrathin-GaN. At 60 mA, the LED with the self-aligned Si barrier gave 6% higher light output than that with the ultrathin-GaN. A headlamp unit using 16 × 16 LED array was demonstrated with the Si self-aligned barrier.