Ta/Au ohmic contacts to n-type ZnO

Ta/Au ohmic contacts are fabricated on n-type ZnO (similar to1 x 10(17) cm(-3)) epilayers, which were grown on R-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD). After growth and metallization, the samples are annealed at 300degreesC and 500degreesC for 30 sec in nitrogen ambient. The specific contact resistance is measured to be 3.2 x 10(4) Omegacm(2) for the as-deposited samples. It reduces to 5.4 x 10(-6) Omegacm(2) after annealing at 300degreesC for 30 sec without significant surface morphology degradation. When the sample is annealed at 500degreesC for 30 sec, the specific contact resistance increases to 3.3 x 10(-5) Omegacm(2). The layer structures no longer exist due to strong Au and Ta in-diffusion and O out-diffusion. The contact surface becomes rough and textured.