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To improve the light-extraction efficiency (LEE) of flip-chip vertical light-emitting diodes (LEDs) grown on silicon carbide (SiC) substrate, embedded photonic crystals (PhCs) were alternatively introduced into the n-GaN layer of LEDs, since etching of the SiC substrate was very difficult. The finite-difference time-domain (FDTD) method was employed to investigate the combination effects of the micro-cavity and the embedded PhCs. The influences of the PhCs configurations on the LEE of LEDs were also examined to get an optimal structure. With the optimized parameters, about 20% enhancement of LEE was achieved comparing to planar SiC substrate-based flip-chip vertical LEDs. The LEE of conventional surface PhCs LEDs and double layer PhCs LEDs were also investigated for comparison. The results indicated that LEDs with carefully designed embedded PhCs could provide more LEE than surface PhCs LEDs. The structures proposed here offered scopes for the design of high-efficiency, high-power LEDs.

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Although the light-emitting diode (LED) has been developed into relative maturity, thermal management remains a very important problem for high-power LED systems. To obtain the temperature distribution and improve the heat dissipation of high-power LED systems, an N-layer model and the analytical solutions to temperature field and thermal resistance are proposed. The equivalent method of fins heatsink is included in modeling. The final analytical solutions are generalized to Nth to adapt flexibly to different system packaging. In particular, the analytical method has obvious advantages in dealing with the thin layer parameter analysis, and it is proved to be accurate and time-saving in comparison with the finite element simulation. The effects of the printed circuit board (PCB) composition and the heatsink on heat dissipation are analyzed in detail, and the related thermo-mechanisms are revealed in terms of thermal resistance. This work can be helpful for the pre-design of high-power LED systems.INDEX TERMS analytical method, heat dissipation, high power-LED system, N-layer model, temperature field, thermal resistance.

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