Improvement of light extraction for AlGaN-based near UV LEDs with flip-chip bonding fabricated on grooved sapphire substrate using laser ablation

Abstract

Mesh-textured flip-chip (FC) structures of AlGaN-based near ultraviolet-light-emitting diodes (NUV- LEDs) are fabricated using an Nd:YAG laser scriber. Compared with the output power of the reference FC-LEDs, those of conventional sapphire substrate (CSS) FC-LEDs and the patterned sapphire substrate FC-LEDs with laser-scribed mesh-textured backsides were improved by 28.7% and 7.2%, respectively. The CSS FC-LED is enhanced using the mesh-textured trench pattern attributable to an increase in the light-extraction efficiency resulting from an increase in the photon-escape probability due to enhanced light scattering at the trench-patterned-sapphire/air interface. Furthermore, the current–voltage curves depict that the laser scribing process does not adversely affect the electrical properties of the FC-LEDs. A Trace-Pro simulation revealed that the laser-scribed-trench CSS FC-LED is effective for light extraction.