Laser Scribing of Sapphire Substrate to Increase Side Light Extraction of GaN-Based Light Emitting Diodes
Generally, the laser scribing was done after GaN-based light emitting diodes (LEDs) growth. This study verified that the utilization of laser scribing leads to an increase in the surface roughness of sapphire substrate sidewalls, which reduces the probability of total internal reflection from light striking the sapphire/air interface. Laser scribing also helps increase side light extraction intensity and output power of GaN-based light emitting diodes. Study results indicated that lasers create a laser scribing layer (LSL) at a depth of approximately 30 μ m after GaN-based LEDs grown in the sapphire substrate undergo laser scribing. Scanning electron microscopy was used to observe the rough surface of the LSL, while near-field optical images verified that rough surface LSL contributes to an increase in side wall light extraction intensity of LEDs. Furthermore, changing the depth of focus of the laser beam (from 0 μm to 36 μm) allows the formation of a large quantity of 3 to 5 μm holes on the LSL. Measurement results indicated that these holes caused the LSL surface to be even rougher, which further strengthened LED side wall light extraction intensity. The results after packaging show that LSL with holes increase output power at 20 mA of GaN-based LEDs by approximately 12.2 %.