Suppression of Ag Agglomeration on Pt-capped ITO/Ag Reflectors for Vertical-type Light-emitting Diodes

The optical output loss originating from Ag metal agglomeration in ITO/Ag reflectors was drastically reduced by inserting a Pt capping layer in vertical light-emitting diodes (VLEDs). The Pt-capped ITO/Ag reflectors showed good Ohmic properties to the p-GaN layer, having a low specific contact resistance of 7.2 x 10(-5) Omega.cm(2) after optimal annealing at 500 degrees C for 1 min. The ITO/Ag/Pt reflectors exhibited high thermal stability, in that nearly the same reflectivity, similar to 82% at 460 nm, was maintained after thermal annealing. On the other hand, in the ITO/Ag reflectors, the reflectivity was severely degraded to 65% by the annealing. Atomic force microscopy monitoring proved that Ag agglomeration was suppressed by the Pt capping layer, allowing the surface roughness to be kept below 1.0 nm after thermal annealing. After chip fabrication, the wafer-level output power of the VLEDs employing the ITO/Ag/Pt reflectors was about 57% higher than that of the VLEDs employing the ITO/Ag reflectors.