Fabrication of a $\hbox {TiN}_{x}/\hbox {Ni/Au}$ Contact on ZnO Films With High Thermal Stability and Low Resistance

A novel contact structure comprising of TiN_1.22/Ni/Au has been deposited on Ga-doped and In-doped zinc oxide (ZnO) epilayer grown on a yttria-stabilized ZrO₂ substrate. It is found that the contact resistivity ρ_c is around 10^-7 Ω cm² for heavily doped ZnO, whereas a ρ_c value of 10^-5 Ω cm² is achieved for ZnO with light doping concentration. Attributed to the barrier effect of TiN_1.22 intermediate layers, thermal annealing does not change the contact resistivity, but it is affected significantly by different surface treatments (atomic oxygen or nitrogen). For atomic oxygen-treated ZnO surface, the carrier density is increased, which leads to lower contact resistivity. It is shown that the contact structure of TiN_1.22/Ni/Au with TiN_1.22 as the intermediate layer can provide a high-quality ohmic contact with low ρ_c and good thermal stability.