Fabrication of SiN_x-based photonic crystals on GaN-based LED devices with patterned sapphire substrate by nanoimprint lithography

SiN_x-based photonic crystal (PhC) patterns were fabricated on the ITO electrode layer of a GaN-based light-emitting diode (LED) device on a patterned sapphire substrate (PSS) by a UV nanoimprint lithography process in order to improve the light extraction of the device. A three-dimensional finite-difference time-domain simulation confirmed that the light extraction of a GaN LED structure on a PSS is enhanced when SiN_x PhC patterns are formed on the ITO top layer. From the I-V characteristics, the electrical properties of patterned LED devices with SiN_x-based PhC were not degraded compared to the unpatterned LED device, since plasma etching of the p-GaN or the ITO layers was not involved in the patterning process. Additionally, the patterned LED devices with SiN_x-based PhCs showed 19%-increased electroluminescence intensity compared with the unpatterned LED device at 445 nm wavelength when a 20 mA current is driven.