An Ni/Ga-doped ZnO layer as a transparent p-type ohmic contact for GaN-based light-emitting diodes

We investigate Ni (3 nm)/Ga-doped ZnO (GZO, 200 nm) transparent conducting layer (TCL) scheme for realizing p-type ohmic contacts for GaN based blue light-emitting diodes (LEDs). Thin Ni layers prohibit plasma damage on a top p-GaN layer of LEDs when GZO layers were subsequently deposited by RF sputtering. The agglomeration of Ni into nano-dot like structures by annealing at 400∼600 °C allows to achieve high transmittance of over 80% at visible wavelengths, a resistivity of 6.5 × 10^-4 Ω·cm, a mobility of 15.1 cm²/V·s, and a carrier concentration of 6.3 × 10²⁰ cm³. Then, an ohmic contact of this layer on a blue LED is achieved with a contact resistance of 1.7 × 10^-2 Omega;·cm²when annealed at 600 °C. The light output power and operation of a blue LED with the proposed TCL are on par with the reference LED with ITO contact layer. These results indicate that the Ni/GZO TCL scheme is a promising non-Indium Scientific Tin Oxide p-type ohmic contact.