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. (C) 2016 The Japan Society of Applied Physics.