The applications of laser in processing of light-emitting diodes
(LEDs) have become popular and inevitable. In this paper, we reported a complete
fabrication process of InGaN LED involving a small modification of substrate by
ultrafast laser. We created structured voids within the pattern sapphire
substrate (PSS) with distributed Bragg reflector (DBR) on the backside by a
tightly focused femtosecond laser. One or two passes of voids were aligned in
rectangular grid shape and a study of different grid spacing was conducted. The
wafers were stealth-diced by the same laser and mechanically cleaved after the
on-wafer light output powers (LOP) are measured at 120 mA nominal current. The
splitted chips are then undergone complete packaging process and LOP is measured
again along with the electrical and irradiation properties. A raise of 1.35% of
average on-wafer LOP is achieved at the optimal condition: 0.2 W total laser
power for two passes of voids (grid spacing 40 µm) at focal depths set at 32 µm
and 64 µm respectively from the backside. Also, the illumination efficiency is
further improved by 4.59% after epoxy molding compound (EMC) packaging. The
voids serve successfully as scattering or diffractive sources to reverse the
stray photons in useful directions. Apart from the enhancement from both PSS and
DBR there is still room for light extraction efficiency (LEE) improvement. The
L-I-V relationship and diffusion angle are also presented.
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