Formation of Thermally Stable AgCu-Based Reflectors by a Two Step Alloy Method for Vertical Light-Emitting Diodes

Two-step alloyed indium-tin-oxide (ITO)/Ni/AgCu/Pt reflectors for high performance GaN-based vertical light emitting diodes (VLEDs) were investigated. The ITO layer was first annealed at 650 degrees C for 1 min in air to make an Ohmic contact and the Ni/AgCu/Pt reflectors were deposited and subsequently annealed at 400 degrees C for 1 min in air to improve their reflectance and mechanical adhesion with the ITO layer. It was shown that the reflectance of the ITO/Ni/AgCu/Pt reflectors at 460 nm was slightly increased from 82 to 87% after two-step annealing Based on the secondary ion mass spectrometry depth profiles, this improvement was attributed to the formation of a transparent Ni-oxide and the existence of Cu atoms near ITO/AgCu/Pt interface regions suppressing the inter and out diffusion of Ag. The VLEDS fabricated with the ITO/Ni/AgCu/Pt reflectors showed an approximately 4 4% higher output power and much better current-voltage characteristics than those with the Ag based reflectors. (C) 2010 The Japan Society of Applied Physics