Reliability of High-Voltage GaN-Based Light-Emitting Diodes

Reliability is important in evaluating semiconductor device quality, although reliability measurement and analysis procedures are complicated. A new type of light-emitting diode (LED), GaN high-voltage (HV) LEDs, is superior to traditional low-voltage LEDs owing to fundamentally higher lighting efficiency and a simpler driving circuit. Recently, HV-LEDs have received much interest, and related commercial devices have been developed. However, reports on HV-LED reliability are very rare. Therefore, herein, we conduct a systematic study of the reliability of commercial HV-LEDs. In current stress-accelerated lifetime testing experiments on HV-LEDs (50 V) for 2,000 h, the luminous flux of white LEDs was reduced by 2.5%–9% and the luminous efficacy by 2.7%–11.3% after aging. The forward voltage was increased, the blue- and yellow-light irradiations of white-light HV-LEDs were reduced, and the excitation efficiency of fluorescence powders was decreased. Detailed analysis is carried out on a sample exhibiting catastrophic failure. The abrupt drop in luminous flux noted can be attributed to cracking of the fluorescent layer and reduction of optical transmittance in the epoxy resin, rather than deterioration in the chip itself. Finally, an improved lifetime-prediction method based on Bayesian statistics is proposed. Compared to conventional lifetime-calculation methods, this method combines experimental data, the conventional model, and historical information rationally. Therefore, it provides lifetime prediction at a higher confidence level: the HV-LED lifetime is estimated as 18 517 h. The results reported can guide the design, manufacturing, and packaging of HV-LEDs, while the new lifetime-estimation method is valuable to reliability evaluation of power electronic devices in the semiconductor industry.