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

AlInGaN-based light emitting diodes (LEDs) emitting in the ultraviolet (UV) wavelength range around 310nm were fabricated using 300nm thick SiN
_x
or SiO
₂
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 SiN
_x
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 SiN
_x
or SiO
₂
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 SiN
_x
layer showed that the insulator with the highest hydrogen content (SiN
_x
by CC-PECVD) resulted in the fastest degradation, while that with the lowest hydrogen content (SiO
₂
by IC-PECVD) showed a slower degradation.