Low specific contact resistance Ti/Au contacts on ZnO

Ti/Au Ohmic contacts on heavily Al-doped (n similar to 10(19) cm(-3)) n-ZnO produce low specific contact resistivity of 2.4x10(-7) Omega cm(2) in the as-deposited condition and extremely low minimum values of 6x10(-8) Omega cm(2) after annealing at 300 degrees C.The contact resistance is independent of measurement temperature after low temperature anneals, suggesting that tunneling is the dominant transport mechanism in the contacts. The contact morphology roughens after annealing at 150 degrees C and Auger electron spectroscopy depth profiling shows Zn outdiffusion through the metal and intermixing of Au and Ti. However, the morphology does not significantly worsen after anneals at 450 degrees C. This metallization scheme looks very attractive for the n-electrode of ZnO-based light-emitting diode structures.