FDTD simulation for light extraction in a GaN-based LED

It is well known that light extraction from an LED can be enhanced by roughening the surface of the LED on a wavelength scale. However, the surface structure for optimal extraction and the underlying physical mechanism for increased emission are still largely unknown. In this work, we present both numerical and experimental studies on light extraction in GaN-based LEDs with square lattice photonic crystal patterns by using large-scale, three-dimensional FDTD (finite-difference time-domain) simulations, and we establish a reasonable simulation environment, including boundary conditions, and practical simulation specs, including source conditions. We show that these numerical results agree reasonably well with the experimental results. In particular, we explain the relationship between frequency and surface structure in light extraction. This allows us to suggest optimal practical structures for enhanced LEDs.