The degradation of high power gallium nitride light-emitting diodes

In this paper, the degradation of bare high power GaN/InGaN blue light-emitting diodes (HP-LEDs) was investigated by considering the electrical, thermal and optical aging characteristics. The HP-LED samples were stressed at the elevated temperature of 85 °C with an injection current of 500 mA. The rated current of the HP-LEDs is 350 mA at room temperature. Changing in tunneling current for the electrical characteristic, a gradual increase for the external quantum efficiency (EQE), a gradual decrease for the light power and the luminous flux were monitored. The luminous intensity distribution is more uneven after degradation. And thermal resistance and temperature rise of chip increase with aging time. In addition, the thermal resistance of the die-attach and ceramic wafer were also increasing after aging. After theoretical calculation, the defect concentration of the die monotonously increases with aging time. Therefore, the responsible factors of these changes were proposed to be the generation of the dopant activation, point defects, dislocations and other defects in the chip level during highly accelerated test. These defects as non-radiative recombination centers make charge carrier cross quantum well structure directly. Thereby, the degradation of the electrical, thermal and optical aging characteristics of HP-LEDs is observed.