Oxygen-controlled structures and properties of transparent conductive SnO2:F films

The morphology and properties of the transparent SnO2:F (FTO) films, deposited by RF magnetron sputtering at varying oxygen flows from 0∼3sccm, were examined. For FTO films deposited with 0∼1sccm O2, the polar unsaturated (101) planes were the preferred orientation, resulting in resistivity values as low as 10−3 Ω cm, and the transparency of 86.5% in the visible range. The saturated (110) orientation planes associated with {101} facets formed knee twin crystallites for the FTO film prepared at 2sccm O2. Further increases of O2 led to severe mis-orientation of the crystals. The average transparency in the visible range increased up to 95%, but these FTO films were hardly conductive due to the oversupply of O2. The optical band gaps became wide at first and then narrow again as the increases of the oxygen flow rates.