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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.

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Two-dimensional (2D) photonic crystal (PhC) patterns in regular four-fold symmetry (2PhC) and dodecagonal symmetric photonic quasicrystal (12PQC) with 970 nm lattice pitch have been formed by electron beam lithography on the surface of GaN-based light emitting diodes (LEDs). The symmetry of a 2D quasicrystal in this work was based on a square-triangle tiling system. The enhancement of light extraction was obtained from both the 2PhC and 12PQC introduced GaN-based LEDs, and 12PQC is favourable compared to 2PhC. To explore the physical properties, we proposed a method for inspecting diffraction behaviours of the PhC arrays. The results supplied a clear representation of the diffraction behaviours of 2PhC and 12PQC that correspond to their lattice symmetry.

This paper focuses on the optical mode analysis of laser diodes to improve light emission. Under the mode analysis, we compare the optical confinement factor (OCF) percentage of the emitting light from the LDs. There are two structures which we analyze: a basic GaN waveguide structure and an InGaN waveguide structure. The second structure has additional InGaN waveguides and is analyzed under two additional design variations: the concentration of Indium and the thickness of the top waveguide layer. The results of this study indicate introducing InGaN waveguide layers correlates with lower order modes (zero and first order) and increase the OCF values. The top InGaN waveguide layer, which has a higher concentration of Indium, appears to increase the OCF. However, the increased thickness of the InGaN layer causes the lower modes’ OFC to decrease. Over all, in the best case, InGaN LD has an OCF of 1.8896%, which is about a 312% improvement compared to that of GaN LD ( OCF=0.4535%).