Ion Beam Surface Modification of GaN Films for High Efficient Light Emitting Diodes

Focused gallium (Ga) ion beam technology has been proposed to modify the surface of GaN thin films. Due to the significant advancement in nitride semiconductors, the solid-state light emitting diodes will gradually replace fluorescent lamps in the next decade. However, further improvements in light extraction and power efficiency are still highly desired. GaN is limited by its high refractive index, with low light escape cone angle at about 24.6°. The external quantum efficiency is low due to the unwanted reflection and absorption. As the patterning technology scales down to the nanometer level, photonic crystal lattice in the visible light wavelength range can be achieved. Therefore, we improved the external efficiency by the new design of hexagonal photonic crystal lattice with air hole arrays in the diameter of 150 nm and the depth of 120 nm. The Ga beam was accelerated at 30 kV and the ion current was 100 pA. The plane wave expansion method along with the finite difference time domain was useful to investigate the quantum confinement. The nanopatterning by the focused ion beam could save time and processing step. In addition, we have successfully prepared blue InGaN/GaN samples with hexagonal period of 200 nm. The device micro-photoluminescence results have demonstrated that the peak illumination intensity was improved by 30%.