High-transmittance NiSc/Ag/ITO p-type ohmic electrode for near-UV GaN-based light-emitting diodes

We report on the formation of NiSc(2.5 nm)/Ag(2.5 nm)/ITO(200 nm) transparent p-type Ohmic electrodes for GaN-based near-UV light-emitting diodes (LEDs). We show that the NiSc(2.5 nm)/Ag(2.5 nm)/ITO(200 nm) contacts become Ohmic with contact resistivity of 4.9 × 10^-3 Ωcm ² and a transmittance of 80 % at 400 nm when annealed at 630 °C for 1 min in air. Near-UV (400 nm) LEDs fabricated with the annealed NiSc/Ag/ITO p-contacts give a forward-bias voltage of 3.69 V at 20 mA and a series resistance of 21.1 Ω, which are better than those for Ni/Au contacts. Based on Auger electron spectroscopy and electrical results, possible Ohmic formation mechanisms are described.