Abstract
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 µm 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 %.
© 2011 IEEE
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