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 (N(d) = 1.79 x 10(16) - 5.76 x 10(18) cm(-3)). For n-ZnO layers with carrier concentrations in excess of 8.04 x 10(17) cm-3, as-deposited ITO contacts produce good Ohmic behavior. However, as-deposited ITO contacts to n-ZnO with carrier concentrations less than similar to 4 x 10(17) cm(-3) yield non-Ohmic behaviors. We show that when annealed at 400 degrees C in a nitrogen ambient; the ITO contacts to ZnO (with carrier concentrations exceeding 4.08 x 10(17) cm(-3)) become Ohmic with a specific contact resistivity in the range of 8.76 x 10(-3) - 1.51 x 10(-4) Omega cm(2). Based on carrier transportation theory, we describe the carrier concentration and the annealing temperature dependence of the carrier transport mechanisms