Analysis of GaN based LED performance before and after the ESD shock

GaN-based LEDs are fast replacing the traditional lighting in numerous applications because of many advantages, such as energy saving and green environments. But as for the high level LED applications, one of the greatest concerns and key requirements is the reliability. In general, GaN epilayers are usually grown on an insulating sapphire substrate since no suitable substrates could be utilized. In this case, except for the degradation of light output power, electrostatic discharge (ESD) is one of the main reliability concerns and draws lots of attention. There are many reported methods[1~3] to overcome the ESD-induced damage, such as combining with a Si-based Zener diode via the flip-chip process, building an internal GaN Schottky diode inside the chip, inserting a high-temperature grown p-type cap layer into an epitaxial structure. But to characterize the ESD endurance, it is normally necessary to operate the ESD shock, which is destructive and irreversible procedure. Therefore, the aim of this study is to compare the electrical and optical properties before and after ESD test, and find out the relationship between the intrinsic structure and ESD characteristic. Three type of LEDs with different structure were prepared and performed using HBM model ESD shock ranging from 0~8KV. I-V, C-V, luminous flux measurements were carried out before and after the ESD test, respectively. The results demonstrate that the ESD endurance can be improved by the inner stress modulation.