Use of an indium zinc oxide interlayer for forming Ag-based Ohmic contacts to p-type GaN for UV-light-emitting diodes

We have investigated indium-doped ZnO(IZO)/Ag Ohmic contacts to p-type GaN for use in UV-light-emitting diodes (LEDs). The as-deposited sample shows rectifying behaviour. However, the samples become Ohmic when annealed at temperature of 330-530 °C for 1 min in air. For example, the contact produces specific contact resistance of 5.51 × 10^-4 Ω cm² upon annealing at 530 °C. In addition, the 530 °C annealed IZO/Ag contacts give reflectance of 82.3% at a wavelength of 405 nm, which is better than that (70.6%) of the single Ag contacts. Near-UV LEDs fabricated with the IZO/Ag contacts give forward voltage of 3.24 V at an injection current of 20 mA, which is better than that with the single Ag contacts. On the basis of x-ray photoemission spectroscopy and scanning transmission electron microscopy results, possible Ohmic formation mechanisms are described.