Abstract
Cr/Al/Ti/Au stacks with two thicknesses of Al layers were employed as reflective n-type electrodes for 274 nm AlGaN-based flip-chip deep ultraviolet light-emitting diodes (DUV LEDs). Large bulges arose in the annealed n-type electrode with 120-nm-thick Al layer, resulting in cracks within the upper rugged SiO2 passivation layer after burn-in test. Sn atoms from solder paste migrated along the cracks and served as leakage current channels, which accelerated device degradation. In contrast, the annealed n-type electrode with 60-nm-thick Al layer retained uniform morphology. And the DUV LEDs with such n-type electrode exhibited good reliability and normalized optical power of 86.8% after burn-in test of 1000 h. This study provides insight into electrode defects related degradation behavior and helps to improve the reliability of AlGaN-based flip-chip DUV LEDs with reflective electrode.
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