Ti ∕ Au n -type Ohmic contacts to bulk ZnO substrates

Electron-beam-deposited Ti ∕ Au ohmic contacts on undoped ( n ∼ 10 17 cm − 3 ) bulk ZnO substrates exhibited as-deposited specific contact resistivity of 3 × 10 − 4 Ω cm 2 , regardless of the polarity (Zn face or O face) of the ZnO substrate. The annealing environment (air or N 2 ) also had no significant effect on contact properties. The specific contact resistivity slightly decreased after annealing at 300°C but started to increase above 350°C. The measurement temperature dependence of specific contact resistivity revealed that the dominant current transport mechanism is field emission even in the moderately doped ZnO. As the annealing temperature increased, some voids were observed on the metal surface, possibly due to reaction of Ti ∕ Au metallization and the evaporation of the oxygen from the ZnO substrate.