Study of Columnar Growth Polycrystalline (Sn, Cr) co-doped In₂O₃ films deposited by sputtering technique for potential gas sensors applications

In this work, (Sn, Cr) co-doped In₂O₃ polycrystalline films were grown at room temperature by sputtering method using a base pressure of ∼5 × 10⁻² mbar (a low vacuum condition) in order to improve the oxidation process and reduce the time of films production. The films were grown using different deposition times by the sputtering technique onto glass substrate using an InCrSn target. The films were thermal annealing (TA) at two different temperatures at 500 and 650 °C in air atmosphere for a period of 2 h. The films were characterized by mean of X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–vis. XRD patterns of films subjected to TA at 500 °C shows a poorly crystallinity with certain degree of amorphicity, evidenced by broad peaks. Meanwhile, films subjected to the TA at 650 °C show a good crystallinity. The formation of the In₂O₃ phase was found in all samples. Meanwhile, the formation of Cr₃O₄ and CrO₂ phases was detected in the thicker and thinner films, respectively. From SEM images the films evidence a columnar growth with a good homogeneity. The optical band energy gap ∼3 eV below to the expected value for In₂O₃ bulk (3.75 eV) was determined in all samples, which was associated to the formation of impurity energy levels within the forbidden band, due to the doping process. Furthermore, the films show a sensing response to acetone gas. These results makes (Sn, Cr) co-doped In₂O₃ a promising system for gas sensing application.