Enhancement in Light Extraction Efficiency of GaN-based Vertical Light-Emitting Diodes by AgCu-based Reflectors

摘要

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 °C in air to make an Ohmic contact and then the Ni/AgCu/Pt reflectors were deposited and subsequently annealed at 400 °C 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 460nm was slightly increased from 82 to 87% after second 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.