Carrier Transport at Metal/Amorphous Hafnium-Indium-Zinc Oxide Interfaces

In this paper, the carrier transport mechanism at the metal/amorphous hafnium-indium-zinc oxide (a-HIZO) interface was investigated. The contact properties were found to be predominantly affected by the degree of interfacial reaction between the metals and a-HIZO; that is, a higher tendency to form metal oxide phases leads to excellent Ohmic contact via tunneling, which is associated with the generated donor-like oxygen vacancies. In this case, the Schottky-Mott theory is not applicable. Meanwhile, metals that do not form interfacial metal oxide, such as Pd, follow the Schottky-Mott theory, which results in rectifying Schottky behavior. The Schottky characteristics of the Pd contact to a-HIZO can be explained in terms of the barrier inhomogeneity model, which yields a mean barrier height of 1.40 eV and a standard deviation of 0.14 eV. The work function of a-HIZO could therefore be estimated as 3.7 eV, which is in good agreement with the ultraviolet photoelectron spectroscopy (3.68 eV). Our findings will be useful for establishing a strategy to form Ohmic or Schottky contacts to a-HIZO films, which will be essential for fabricating reliable high-performance electronic devices.