Porous Light-Emitting Diodes With Patterned Sapphire Substrates Realized by High-Voltage Self-Growth and Soft UV Nanoimprint Processes

Nanostructured GaN-based light-emitting diode (LED), with its high performance on light extraction efficiency, has attracted significant attention for the potential application in solid state lighting. However, patterning structures at nanoscale feature size with large area and low cost is of great importance and hardness. In this paper, a 2 inch anodic aluminum oxide (AAO) template was used as the initial mold to copy the photonic-crystal-like structures (PCLSs) on a blue-light LED by soft UV nanoimprint lithography. An additional solute, aluminum oxalate hydrate, is employed to overcome the burn-through issue in the high-voltage anodization which is critical for the fabrication of the large-pore (250-500 nm) AAO. The photoluminescence and electroluminescence enhancements of the patterned LED device with 150-nm-deep PCLSs are, respectively, 45% and 11.4% compared with the un-patterned LED device. A 3-D finite-difference time-domain simulation confirms that the light extraction efficiency is enhanced when PCLSs are formed. The proposed method is simple, cheap, repeatable in large area and compatible with the high volume production lines.