Study on photoluminescence of GaN-based UV-LEDs with refractive index gradient polymeric nanopatterns

For the GaN-based UV-light emitting diodes (LEDs), a lot of studies have been performed to improve the internal quantum efficiency; however, low external extraction has been another confronting problem. Here, we constructed nanopatterned polymer layers on UV-LEDs. Employing curable polymer (P4MS), nanopatterned polymer layers were successfully prepared on UV-LEDs by curing the pre-deposited first layer and imprinting the second uncured layer with the nanopatterned soft mold, followed by UV curing. We considered the nanostructured P4MS layers as multiple layers from bottom to top, which is expected to improve external light extraction of UV-LEDs with small difference of refractive indices. As compared to the bare LED, PL intensity showed about 25% increment for the surface-treated UV-LEDs with nanopatterned polymer in blue light region in thickness of continuous layer from 21 to 120 nm.