Impact of Insulators and Their Deposition Method on the Reliability of AlInGaN-Based UVB LEDs

Abstract

AlInGaN-based light emitting diodes (LEDs) emitting in the ultraviolet (UV) wavelength range around 310nm were fabricated using 300nm thick SiNx or SiO2 layers deposited by different types of plasma enhanced chemical vapor deposition (PECVD) for electrical insulation. The composition, deposition technique, and thermal treatment of the insulator were varied and its influence on the breakdown voltage, step coverage, and degradation behavior of the UVB LEDs was studied. LEDs with SiNx layers deposited by PECVD in a capacitively coupled (CC) deposition process at high temperatures showed the highest conformity, highest breakdown voltages, but also the fastest degradation. The degradation was reduced by annealing the wafers after the insulator deposition. If the SiNx or SiO2 was deposited by inductively coupled IC-PECVD instead, the conformity and breakdown voltages decreased. Insulators deposited by IC-PECVD showed a high rate of sudden failures during the first 1,000h of operation. Studies of the hydrogen content in the SiNx layer showed that the insulator with the highest hydrogen content (SiNx by CC-PECVD) resulted in the fastest degradation, while that with the lowest hydrogen content (SiO2 by IC-PECVD) showed a slower degradation.