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(18) 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) Omega 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) Omega cm(2) when annealed at 700 degrees 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 degrees 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. (c) 2005 The Electrochemical Society. [DOI: 10. 1149/1.1854591] All rights reserved.