Highly reflective and low resistance indium oxide/Ag ohmic contacts to P-GaN for flip-chip light emitting diodes

We have investigated Mg- and Cu-doped In₂O₃/Ag schemes for the formation of high-quality ohmic contacts to p-type GaN for high power flip-chip light emitting diodes (LEDs). It is shown that the doped In ₂O₃/Ag contacts produce specific contact resistance in the range of ∼10^-4 - ∼10^-5 ωcm² and reflectance of about 90% at a wavelength of 460 nm when annealed at 530°C for 1 min. It is also shown that unlike single Ag contacts, the doped In ₂O₃/Ag contacts are fairly stable without surface and interface degradation although annealed at 530°C for 1 min in air ambient. In addition, blue InGaN/GaN LEDs fabricated with the annealed In ₂O₃/Ag contact layers give forward-bias voltages of 3.0 - 3.15 V at an injection current of 20 mA. The results strongly indicate that the doped In₂O₃/Ag scheme can be a highly promising p-type contact for high power GaN-based FCLEDs for solid-state lighting application.