Design principles of external and internal patterns for efficient light extraction

We studied external and internal patterns for boosting light extraction from GaN light-emitting diodes (LEDs). With a transparent conductive layer (TCL) inserted between an external pattern and an upper GaN plane, light extraction increased in a thin, high-refractive-index TCL. A periodic array of air voids embedded in a GaN medium yielded an extraction efficiency similar to the external pattern's one. For double-layer patterns, as the internal pattern was close to multiple quantum wells within a wavelength, the extraction efficiency was enhanced ∼30% over that of a single-layer pattern. This work will be useful for designing blue-to-ultraviolet-emitting GaN-based LEDs with multi-layer patterns.