Thickness dependence of electrical and optical properties of sputtered nickel oxide films

Nickel oxide thin films were deposited by RF magnetron sputtering process in a pure oxygen atmosphere at RF power 200 W with substrate unheated and heated for 400 °C, respectively. Different sputtering time produced different thickness of films. Sheet resistance and resistivity were measured using four probe and Hall effects for analyzing electrical properties. The results show the lowest sheet resistance, which was 16.87 kΩ/□, and resistivity, which was 0.69 Ω cm, could be obtained in the condition of substrate unheated with a film of 200 nm thickness. The transmittance of films will decrease as the thickness of films increasing. Crystalline properties of NiO films were investigated as a function of film thickness using X-ray diffraction. The preferred orientation of NiO film is (111) as substrate unheated. It will become (200) when the substrate temperature is at 400 °C. With same film thickness, substrate unheated has larger grain size than the substrate with temperature of 400 °C.