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 similar to 600 degrees C allows to achieve high transmittance of over 80% at visible wavelengths, a resistivity of 6.5 x 10(-4) Omega . cm, a mobility of 15.1 cm(2)/V . s, and a carrier concentration of 6.3 x 10(20) cm(3). Then, an ohmic contact of this layer on a blue LED is achieved with a contact resistance of 1.7 x 10(-2) Omega . cm(2) when annealed at 600 degrees C. The light output power and operation voltage of a blue LED with the proposed TCL are on par with the reference LED with an ITO contact layer. These results indicate that the Ni/GZO TCL scheme is a promising non-Indium Tin Oxide p-type ohmic contact.