Enhancement of light extraction in GaN-based light-emitting diodes by Al2O3-coated ZnO nanorod arrays

We report on the improvement of light extraction efficiency in blue light-emitting diodes (LEDs) by the use of Al2O3/ZnO core/shell nanorods (NRs) grown on the surface of the LED epi-structure. The electroluminescence intensity at a current injection of 20 mA of LEDs with 40 nm-thick Al2O3-coated ZnO NR arrays is 2.1 and 4.0 times than those of LEDs with bare ZnO NRs and no NRs, respectively. The enhanced light extraction of LEDs with Al2O3-coated ZnO NRs can be attributed to an increase in transmission and improved light extraction probability for photons generated in blue LEDs due to a reduction of Fresnel reflection loss.