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ment o sed a ling i ase, A rmore syste ling, t ed the 0 nm fied tr dary-i u con p-type 593 A receiv LEDs require high light extraction efficiencies and high internal ambient. To measure the specific contact resistance, photolithogra-phy techniques were used to pattern a modified transmission line e Lett 25.00 Downloquantum efficiencies. Because flip-chip1 and vertical-structure2,3 GaN-based LEDs exhibit superior light extraction and heat-sink ef-fects, they exhibit an enhanced device performance. These two types of LED structures are fabricated by using high reflectance, low con-tact resistance p-type alloy contacts, such as Ag layers.4 Unfortu-nately, these Ag layers exhibit a poor thermal stability of their re-flectance and ohmic contact on p-type GaN as a result of Ag aggregation during thermal annealing.5 Several alternative materials have been investigated to obtain reliable Ag-based ohmic contacts on p-type GaN, including Ni/AgAl,5 Cu–Ni solid solution/Ag,6 Ag/Cu,7 Ni/Ag/Ru/Ni/Au,8 and Ni/Ag-annealed/Au.9 In this study, we compared the thermal stability for reflectance and ohmic contact of Ni/Ag, Ni/Ag/Au, and Ni/Ag/Ti/Au layers on p-type GaN. Based on our analytical results, we propose a mechanism for the reflective ohmic contact on p-type GaN. Experimental Taiyo Nippon Sanso SR2000 metallorganic chemical vapor deposition was used to grow the p-type GaN on a c-plane sapphire substrate. Trimethylgallium, trimethylindium, and ammonia NH3 were used as sources; biscyclopentadienylmagnesium CP2Mg was the p-type dopant. The structure of the p-type GaN comprised a 30 nm thick GaN buffer layer, a 2 m thick undoped GaN layer, and a 1 m thick Mg-doped GaN layer. After growth, the sample was treated in a quartz furnace for activation under a N2 ambient. The annealing temperature and time model10 on the p-type GaN. The reflectance at 465 nm was also measured spectrometrically for the contact metal deposited onto a glass substrate. The three structures of the contact metal were also deposited onto p-type GaN for characterization by using scanning electron microscopy SEM and secondary-ion mass spectrometr