Improvement of thermal stability of Ag-based reflector in GaN-based flip chip LEDs by electron-beam irradiation

Abstract

We proposed the effects of electron-beam irradiation (EBI) on the Ag reflector for GaN-based light-emitting diodes (LEDs). To evaluate the thermal stability of Ag, we carried out a thermal aging test. The Ag with EBI showed a high reflectance of 97.9% at a 450 nm wavelength and higher thermal stability than the Ag reflector without EBI. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) were used to examine the surface and texture evolution of the Ag reflector before and after thermal aging at 300 °C for 120 min. SEM and EBSD showed that unlike the agglomeration occurred in the Ag reflector without EBI, the Ag reflector with EBI only showed an increase in grain size after thermal aging at 300 °C for 120 min. XRD data demonstrated the Ag reflector to have a higher -peak intensity due to EBI. On the other hand, after thermal aging at 300 °C for 120 min, the Ag reflector with EBI becomes less -peak than the Ag reflector without EBI. The difference in the surface and texture between the Ag reflectors with/without EBI is closely related to the changes in grain size and surface energy by thermal aging.