Carrier Concentration Dependence of the Electrical Behaviors of ITO Contacts on n-Type ZnO

Abstract

We report on the carrier concentration dependence of the electrical characteristics of ITO Ohmic contacts to unintentionally doped n-ZnO (Nd = 1.79 1016 { 5.76 1018 cm 3). For n-ZnO layers with carrier concentrations in excess of 8.04 1017 cm 3, as-deposited ITO contacts produce good Ohmic behavior. However, as-deposited ITO contacts to n-ZnO with carrier concentrations less than 4 1017 cm 3 yield non-Ohmic behaviors. We show that when annealed at 400 C in a nitrogen ambient, the ITO contacts to ZnO (with carrier concentrations exceeding 4.08 1017 cm 3) become Ohmic with a speci c contact resistivity in the range of 8.76 10 3 1.51 10 4 cm2. Based on carrier transportation theory, we describe the carrier concentration and the annealing temperature dependence of the carrier transport mechanisms