Design of an LED chip structure with an integrated two-dimensional photonic crystal to enhance the light-extraction efficiency
We numerically simulated the light-extraction efficiency of light-emitting diodes (LEDs) with an integrated two-dimensional photonic crystal (PC) structure on the top surface in order to enhance light extraction. We considered InGaN-based LED chips with a typical emission wavelength of λo = 460 nm and an emission wavelength inside the LED chip of λ = λo/nGaN, where nGaN is the refractive index of GaN. We used positive (relief) and negative (intaglio) patterns for the PC structures with square arrangements. The pattern period (Λ), width (d), and height (h) of the PC structure were varied systematically in the PC-LEDs; then the light-extraction efficiency of each PC-LED was simulated numerically using a three-dimensional finite-difference time-domain method to optimize the PC structure in terms of light extraction. The PC LED with a square pilla pattern with Λ ≃ 1.4λ, d ≃ 0.75Λ, and h ≃ 0.75Λ had the maximum light-extraction efficiency for positive patterns while the cylindrical hole pattern with Λ ≃ 1.2λ, d ≃ 0.5Λ, and h ≃ 0.5Λ had the maximum light-extraction efficiency for negative patterns.