Thermally Stable and Low Resistance Re/Ti/Au Ohmic Contacts to n ­ ZnO

We report on the formation of thermally stable ohmic contacts on n-type ZnO:Al (n d = 2 X 10 1 8 cm - 3 ) using a Re/Ti/Au metallization scheme. It is shown that the as-deposited Re/Ti/Au contact is ohmic with a contact resistivity of 2.1 X 10 - 4 Ω cm 2 . The electrical characteristics of the samples are further improved upon annealing, namely, the sample produces a specific contact resistance of 1.7 X 10 - 7 Ω cm 2 when annealed at 700°C for 1 min in a nitrogen ambient. Atomic force microscopy results show that the surface of the samples is reasonably smooth with a root-mean-square roughness of 6.0 nm when annealed at 700°C. The carrier transport mechanism is described using the relationship between temperature and specific contact resistance. Based on X-ray diffraction and X-ray photoemission spectroscopy results, the ohmic mechanism for the annealed samples is also described and discussed.

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