*3.3. E*ff*ects of Annealing Temperature on Electrical Resistivity*

Figure 2 shows the electrical properties of the as-deposited and annealed Ti:SnO2 films. Previous studies have shown that the TCO transmission mechanism is governed mainly by element doping and oxygen vacancies [29,30]. For the Ti:SnO2 thin films considered in the present study, the oxygen vacancy contributes two free electrons, and therefore dominates the transmission mechanism. Although the Sn<sup>+</sup> atom also provides a free electron, it cannot be activated as effectively as the oxygen vacancy because the carrier concentration is primarily controlled by the oxygen vacancy. As described above, the Ti:SnO2 film has a small crystal structure in the as-deposited condition and under an annealing temperature of 200 ◦C. However, as the annealing temperature is increased to 300 ◦C, the film has a low resistivity of 5.65 <sup>×</sup> 10−<sup>3</sup> <sup>Ω</sup>·cm as a result of the high carrier concentration. Meantime, as the annealing temperature is increased beyond 300 ◦C, the SnO and SnO2 combined phase are gradually formed, causing the carrier concentration to decrease and the resistivity to increase.

**Figure 2.** Electrical properties of as-deposited and annealed Ti:SnO2 films.
