Analysis of gallium nitride light emitting diode by waveguide theory and optimization of light extraction efficiency via patterned dielectric interface

Owing to the existence of high index gallium nitride (GaN) confinement layer, most of the light generated inside the active layer of GaN-based light emitting diode (LED) is converted to guided optical wave, propagating back and forth in the confinement layer, and fails to emit outwardly. This waveguide effect prevents light from being extracted from inside LED; therefore the extraction efficiency remains poor for such device. This study reports analysis of LED structure by waveguide theory and optimization of light extraction efficiency via patterned dielectric interface, of which the pattern was determined by satisfying momentum matching condition for coupling of bound mode to radiation mode. The proposal was validated by finite difference time domain (FDTD) simulation of top emitting GaN LED, in which the proposed pattern was respectively induced on GaN surface and sapphire substrate. The resultant structure exhibited significant extraction efficiency enhancement over conventional unpatterned LED. And two mechanisms for the enhancement – mode coupling and wave scattering – were compared. The results also revealed that the favorable location for the top emitting GaN LED to induce patterned dielectric interface is on the GaN surface.