High-efficiency Si-gel-encapsulated GaN-based photonic crystal blue light-emitting diodes

Highly efficient Si-gel-encapsulated GaN-based blue light-emitting diodes were realized by introducing square-lattice photonic crystal patterns (a = 1200 nm) into their top layers. Absorptive three-dimensional finite-difference time-domain computations for a broad range of lattice constants (200 ∼ 3000 nm) were investigated to optimize the enhancement of the light output. Integration sphere measurements were used to show that there are relative enhancements of ∼35 % and ∼70 % before and after encapsulation respectively with a dome-shaped Si gel. The achievable relative enhancement was estimated by using the ray-tracing method. In addition, the radiation from the encapsulated light-emitting diodes was found to be distributed over a relatively narrow angular spread.