Improvement of light extraction from GaN-based thin-film light-emitting diodes by patterning undoped GaN using modified laser lift-off

To improve light extraction from GaN-based light-emitting diodes (LEDs), we demonstrated an approach of modified laser lift-off (M-LLO) technique for patterning undoped GaN (u-GaN). The M-LLO consists in sequentially forming a two-dimensional triangular lattice pattern with a 4μm period on a polymer layer over a sapphire substrate backplane by UV imprint and delivering the pattern onto u-GaN accompanied with the removal of the sapphire substrate. The enhancement of light extraction from GaN-based M-LLO LED with a reflective Ag film on the 120nm deep u-GaN pattern was about 31% and 100% compared to that of a LLO-LED with a reflective film and a conventional LED with a sapphire substrate, respectively.