Semiconducting properties of CoO thin films

This paper reports electrical properties of CoO thin films of different thickness in the range 0.375 – 7.95 µm. Both electrical conductivity and thermopower were measured at elevated temperatures (1223 – 1423 K) and under controlled oxygen partial pressure (5 − 2.1x104 Pa). It was found that at low p(O2) the electrical conductivity decreases with film thickness. The activation energy of the electrical conductivity (Ea) in air decreases with the oxide thickness from 0.56 eV at 0.375 µm to 0.52 eV for massive CoO while at low p(O2)=5 Pa the Ea is independent of the thickness (Ea = 0.46 eV). The reciprocal of the p(O2) exponent of the electrical conductivity (nδ) in the range 1223 K – 1373 K is close to four for the 7,95 µm film and is about 3.5–3.7 for the 0.375 µm film. The electrical properties of the CoO thin films are considered assuming different defect structures in the bulk phase and the surface layer.