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 degrees 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 Cr3+, 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 (Cr3+ and Cr6+) and host ions (In3+), consequently, increases the carrier concentration. The decrease in carrier mobility (approximate to 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 approximate to 1 at. % Cr content has optimum opto-electronic properties, an average transmittance of approximate to 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 x 10(-5) ohm.cm, carrier density 2.2 x 10(21) cm(-3), and carrier mobility of 36.7 cm(2) V-1S-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.