GaN-Based Light-Emitting Diodes Directly Grown on Sapphire Substrate with Holographically Generated Two-Dimensional Photonic Crystal Patterns

As an approach to enhance light extraction from GaN-based light-emitting diodes (LEDs), we inserted a submicron period photonic crystal (PC) pattern at the interface between GaN epilayer and sapphire substrate. A two-dimensional square-lattice pillar array of 600-nm period was produced directly onto the sapphire substrate by a combination of laser holography and inductively-coupled-plasma etching. A standard GaN LED heterostructure was grown on top of the nano-patterned substrate, which was then processed to conventional bottom-emitting LED chips. At the drive current of 20 mA, the PC-LED produced surface-normal output power about 40% higher than that of the reference LED (with no PC integrated). Temperature-dependent photoluminescence measurement indicated that the emission enhancement was solely a structural effect by the integrated PC pattern.

C-plane sapphire substrate misorientation angle on metalorganic chemical vapor deposition of GaN nucleation layers. The angle from c-plane sapphire was varied between 0.05° and 0.30°, tilted towards the m-plane axis. Structural and optical characterization techniques demonstrate an improvement of surface morphology and crystalline quality of GaN nucleation layers as the miscut angle approaches 0.30°. These results correlate well with our previous study of miscut angle on full light-emitting diode structures.


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