Thermal stability of tungsten-based Schottky contacts to N-type ZnO

Rectifying contact formation on n-type bulk single crystal ZnO using W, W₂B and W₂B₅ was studied. The metallization schemes were deposited by sputtering and investigated using current-voltage, scanning electron microscopy and Auger Electron Spectroscopy (AES) measurements. Asdeposited contacts exhibit ohmic and convert to rectifying upon annealing at 600 to 700 °C. The W contacts became rectifying with barrier heights of 0.45 eV without ozone cleaning and 0.49 eV with ozone cleaning and ideality factors of ∼2. When a single Au overlayer was used to reduce the metal sheet resistance, the contacts were ohmic for all annealing conditions. In sharp contrast, a bilayer of Pt/Au produced rectifying contacts with barrier heights of ∼0.4 eV for W₂B and 0.66 eV for W₂B₅ annealed at 600°C, although at this condition the contact showed a reacted appearance and AES showed almost complete intermixing of the metallization.