Morphological stability of Ag reflector for high-power GaN-based vertical light-emitting diode by addition of Ni layer

• Ni-combined Ag contacts shows better morphological stability than Ag only reflector.
• Ni-combined Ag contacts contain only hillocks even after annealing at 300 °C for 60 min.
• Ag only samples are more 〈1 1 1〉-textured than Ni-combined Ag samples after annealing.
• Improved stability is described by combination of thermal stress and surface energy.

We investigated the reasons why Ag reflectors in vertical light-emitting diodes showed much better morphological stability with the addition of an intermediate Ni layer by means of X-ray pole figures, scanning electron microscopy (SEM), and SEM electron backscatter diffraction (EBSD) techniques. The SEM results showed that, unlike the pitted Ag-only contacts, the Ni-combined Ag contacts annealed at 300 °C contained only hillocks, even after annealing for 60 min. The EBSD results demonstrated that the Ag-only samples were more strongly 〈1 1 1〉-textured than the Ni-combined Ag samples after annealing for 60 min. The pole-figure results also indicated that, for both the samples, the {1 1 1} texture was enhanced by annealing, although the Ag-only samples were more highly 〈1 1 1〉-textured than the Ni-combined Ag samples. On the basis of the SEM, EBSD, and pole-figure results, we interpret and discuss the possible mechanisms underlying the improved morphological stability of the Ni-combined Ag reflectors.