Electrical properties of undoped and Li-doped NiO thin films deposited by RF sputtering without intentional heating

The fundamental transmittance and electrical properties of undoped and Li-doped NiO thin films deposited by conventional RF sputtering without intentional heating were evaluated. Both the transmittance and resistivity of undoped and Li-doped NiO decreased with increasing O 2 fraction in the sputtering gas, f (O 2 ) = O 2 /(Ar + O 2 ). The result is attributed to the increase in the concentration of acceptors of Ni vacancies (V Ni ) under oxygen-rich growth conditions. In addition to V Ni , Li atom on the Ni site (Li Ni ) likely acts as a shallow accepter, which can explain the experimental finding that the carrier concentration of Li-doped NiO was approximately three orders of magnitude higher than that of the undoped case deposited under the same f (O 2 ). The mobility of NiO was remarkably low (around 0.1–1.0 cm 2 V −1 s −1 ) and almost independent of f (O 2 ) or the amount of doping, reflecting the large hole effective mass.