Effect of chromium-doping on structure and opto-electronics properties of nanostructured indium tin oxide thin films

Indium-tin-oxide (ITO) thin films co-sputtered with chromium (Cr) have been studied for their structural, electrical, and optical properties. The fabrication has been carried out at room temperature in oxygen-deficient environment under different sputtering power on chromium target followed by thermal annealing in air at 300 °C for 1 h. Experimental characterizations reveal a decrease in grain, crystallite size, increase in crystallinity, and major diffraction peak (222) shift towards higher angle with increase in Cr-doping content. XPS spectra confirmed the presence of Cr as Cr 3+ , Cr 6+ oxidation state, and oxygen vacancies in Cr-doped ITO thin films. The presence of more structural defects due to difference in ionic radii between dopant (Cr 3+ and Cr 6+ ) and host ions (In 3+ ), consequently, increases the carrier concentration. The decrease in carrier mobility (≈ 18%) is caused by the disordering related to increase in Cr content and decreased crystallite size that favor surface trapping states. UV–Vis spectroscopy showed that ITO thin film having thickness of 300 nm doped with ≈ 1 at. % Cr content has optimum opto-electronic properties, an average transmittance of ≈ 86% in the visible range (380–780 nm), and band gap of 3.82 eV. For the same Cr-doping, four-point probe investigation indicates resistivity of 7.65 × 10 –5 Ω.cm, carrier density 2.2 × 10 21 cm −3 , and carrier mobility of 36.7 cm 2 V −1 S −1 . The significant decrease in resistivity of approximately nine times in produced thin films compared with relevant work in literature is the combined effect of Cr-doping and annealing which affect the carrier density and crystallinity.