Buried photonic crystals are an effective way of modifying the far-field pattern from light-emitting diodes. By creating the active region after the photonic crystal is defined, etch-related damage to the device can be avoided. In addition, stronger coupling of the emission to the photonic crystal can be achieved when compared with surface photonic crystals. The interaction of the active region with the photonic crystal is then governed by the profile of the optical modes within the high-refractive index semiconductor.
In the Editor's Choice article on pp. 451–455, Philip A. Shields et al. report finite difference time domain simulations and far-field photoluminescence experiments of full LED devices consisting of deep-etched photonic quasi-crystal structures capped by InGaN/GaN quantum wells. It is found that there is a strong interaction with the dominant low order mode when the coalesced layer thickness is reduced. However, there is still a significant contribution from high-order modes.
The upper front cover image shows a far-field light intensity emission pattern at 475 nm whilst the lower image shows a schematic of the device structure.