Laser lift-off process for blue GaN micro-LED automotive digital headlights

Abstract

Laser lift-off (LLO) is a critical bottleneck in the fabrication of micro-light-emitting diode (micro-LED)-based automotive digital headlights. In this work, a patterned sapphire substrate was successfully removed from a 0.61-in. monochromatic GaN-based blue micro-LED array using a laser lift-off process. The micro-LED chip has a pixel size of 32 × 32 μm2 and a resolution of 370 × 110. LLO was performed on the bonded micro-LED chip using a 248 nm KrF excimer laser. Optical microscopy and scanning electron microscopy observations reveal that the GaN layer in the light-emitting regions remains intact after the LLO process. A comprehensive analysis of the optoelectronic properties of the micro-LED before and after LLO was performed. The current–voltage (I–V) characteristics indicate that the turn-on voltage remains essentially unchanged after the LLO/HCI process. In addition, electroluminescence spectra measured at different injection currents reveal a slight blueshift of the peak wavelength after lift-off. The luminance and external quantum efficiency are enhanced by 33% and 22.7%, respectively. These results demonstrate the effectiveness of LLO in optimizing micro-LED performance and highlight its potential for advanced display applications, providing a scalable solution for subsequent LLO and laser-based mass transfer processes.