Formation and effect of thermal annealing for low-resistance Ni/Au ohmic contact to phosphorous-doped p-type ZnO

We report on a Ni (30 nm)/Au (80 nm) metallization scheme for low-resistance ohmic contacts to the phosphorus-doped p-type ZnO with a hole concentration of 1.0 X 10(18) cm(-3). As-deposited Ni/Au contacts to p-type ZnO showed a specific contact resistance of 7.67 X 10-3 Omega cm(2) by forming Ni-Zn phase to increase the hole concentration near the ZnO surface. The specific contact resistance was decreased with increasing the thermal annealing temperature. When the Ni/Au contact was annealed at 600 degrees C for 30 s in an air ambient, the specific contact resistance was greatly decreased to 1.72 X 10(-4) Omega cm(2). The improved ohmic property was attributed to an increase in the hole concentration by the formation of Ni-Zn and Au-Zn phases due to the outdiffusion of Zn during the thermal annealing process. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.1855832] All rights reserved.