Metals and ITO Contact Nature on ZnO and NiO Thin Films

Abstract

The electrical contact nature between metal and semiconductor plays a key role in the devices operating and performance. An investigation of the contact ohmicity of different metals with p-NiO and n-ZnO semiconducting material is addressed in the present work. The investigated metals are the commonly used ones: Au, Cu, Mo, Ti, Ag, and indium tin oxide (ITO). All the studied metals lead to an ohmic contact with NiO and ZnO semiconductors expected in the case of ITO on NiO where the contact was rectifying. The formation of ohmic contact is explained in terms of the difference between the metal work function and the semiconductors affinity in one hand and on the other hand, in terms of highly doped interface formation due to the oxygen vacancies appearance, reducing then the depletion layer width which favors the carrier transport through tunneling effect. High sheet resistance is measured when using Ag metal as a contact on both ZnO and NiO, due to the diffusion of the latter in the film bulk and to the formation of Ag cluster. Mo, as well, leads to higher sheet resistance when used on NiO due to the metal diffusion. However, due to the conduction band gap offset at the interface ITO/NiO and ITO /ZnO, ITO leads to a Schottky contact with NiO and ohmic one with ZnO.