Abstract
A micro- and nanoscale complex structure made of a high refractive index polymer (n = 2.08) was formed on the ITO electrode layer of an edge-emitting type GaN blue light-emitting diode (LED), in order to improve the photon extraction efficiency by suppressing total internal reflection of photons. The nanoimprint lithography process was used to form the micro- and nanoscale complex structures, using a polymer resin with dispersed TiO2 nano-particles as an imprint resin. Plasma processing, such as reactive ion etching, was used to form the micro- and nano-scale complex structure; thus, plasma-induced damage to the LED device can be avoided. Due to the high refractive index polymeric micro- and nanostructure on the ITO layer, the electroluminescence emission was increased up to 20%, compared to an identical LED that was grown on a patterned sapphire substrate to improve photon extraction efficiency.
Highlights
High brightness GaN-based light-emitting diodes (LEDs) have been widely used for solid-state lighting sources due to their low power consumption, long lifetime, compact form factor, and eco-friendly nature [1,2,3]
The atomic force microscopy (AFM) images of the micro- and nanoscale complex structure that formed on the N-face n-GaN surface, replicated polymer mold, and LED device are shown is Figure 2a,c, respectively
The micro- and nanoscale complex structures were formed on the LED devices using the nanoimprint process
Summary
High brightness GaN-based light-emitting diodes (LEDs) have been widely used for solid-state lighting sources due to their low power consumption, long lifetime, compact form factor, and eco-friendly nature [1,2,3]. Many attempts have been made to maximize the external quantum efficiency (photon extraction efficiency) of LEDs. much room remains for improvement of the external quantum efficiency. One of the biggest issues surrounding the current high brightness LEDs is their low light extraction efficiency (hext) due to the total internal reflection (TIR) of light at the interface of the LED structure with ambient [6]. Various attempts, including surface roughening [7,8], the formation of photonic crystals [9,10], the use of patterned sapphire substrates (PSS) [11,12], and the use of an airgap structure inside the LED [13], were made to suppress the TIR
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