XPS Investigation of Indium-Saving Indium–Tin Oxide (ITO) Thin Films

Indium–tin oxide (ITO) thin films with reduced to 50 mass.% indium oxide content are grown by direct current (DC) sputtering of ITO target in mixed argon–oxygen atmosphere onto glass substrates preheated at 523 K. The films showing the best electrical properties are subsequently heat-treated in air at temperatures of 523 and 623 K for 60 min. X-ray photoelectron spectroscopy (XPS) and x-ray emission spectroscopy (XES) are used for samples’ characterization. Effects of oxygen-flow rate, Sn con-tent, and heat-treatment temperature on electronic properties are studied and discussed. XPS measurements show that indium is in In³⁺ charge state, and tin is only in Sn⁴⁺ state in indium-saving ITO thin films sputtered at different conditions and heat-treated at different temperatures. As-deposited indium-saving ITO thin film sputtered at 0.5 cm³STP/min oxygen-flow rate, which demonstrates the highest conductivity among the as-deposited thin films, shows the highest relative intensity of O_II peak. The electron density of states increases when going from indium-saving thin film to typical ITO one.