Analysis of failure mechanism of GaN-based white light-emitting diode

Abstract

Accelerated aging and life-time tests at ambient temperatures of 40 ℃,70 ℃ and room temperature were carried out on GaN-based white light-emitting diodes (LEDs). The electrical, optical and thermal characteristics of the device were compared before and after different aging times in order to investigate the failure mechanism of the device. Here, we mainly analyzed the failure mechanism related with the chip and the phosphor of the LED. The current-voltage characteristics demonstrated that both the series resistance and the tunnel current increase under lower forward voltages after aging, which were due to the degradation of p-type ohmic contact and the increase of defect density. The thermal characteristics confirmed that the thermal resistance increased rapidly under high aging temperature. This was mainly attributed to the fracture of different materials inside the devices caused by the difference in thermal expansion coefficients. Optical measurements indicated that high aging temperature could accelerate the degradation of output power and reduce the conversion efficiency of the phosphor as well. Finally, the life time of the device was calculated using Arrhenius-equation, and the failure mechanism was analyzed.