Applying photonic crystals with Light Emitting Diodes (LEDs) to improve the light extraction efficiency have been demonstrated successfully. ZnO has been considered as a promising material for the development of next generation UV LEDs with high brightness due to its direct band gap (3.37eV) at room temperature and it has relatively large exciton binding energy. Recently, n-ZnO/p-GaN heterojunction LEDs have been fabricated by several groups. However there has not any experimental evidence yet to integrate photonic crystal with n-ZnO/p-GaN heterojunction LEDs. This paper reports fabrication of n-ZnO photonic crystal/p-GaN LED by nanosphere lithography to further booster the light efficiency.

Usually, electron beam lithography is employed to fabricate the photonic crystals, however, it is a cost process and not suitable for large area production. In our paper, the fabrication of ZnO photonic crystals is carried out by nanosphere lithography (NSL) using inductively-coupled-plasma reactive ion etching (ICP_RIE) with CH4/H2/Ar plasma on the n-ZnO/p-GaN heterojunction LEDs. NSL is a simple and relatively cheaper technique and allows for large-area production. The CH₄/H₂/Ar mixed gas gives high etching rate of n-ZnO film which yields a better surface morphology and results less plasma-induced damages of the n-ZnO film.

The periocity of n-ZnO photonic crystal is designed to fit the spectrum of n-ZnO/p-Gan LED by a Matlab code which suggests an optimum lattice parameter is 200 nm and the air-filling factor of the n-ZnO photonic crystal ranges from 0.35 to 0.65. In our paper we will show our recent result that a ZnO photonic-crystal cylinder has been fabricated by using polystyrene-nanosphere mask with lattice parameter of 200 nm and radius of hole around 80 nm. Experiment results were discussed in detail in terms of surface morphology , photonic-crystal nano-structure and plasma-induced damages which were measured by atomic force microscope, scanning electron microscope and photoluminescence spectrometer respectively.