Heat treatment effects on electrical and optical properties of ternary compound In2O3–ZnO films

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Heat treatment effects on the electrical and optical properties are investigated for In2O3–ZnO film with a Zn content [Zn/(In+Zn)] of 33 at. %. Thin films deposited in a mixed gas atmosphere (Ar+20% O2) by a magnetron sputtering method show high resistivity of about 1.7×10−1 Ω cm. A mixture of In2O3 (99.999%) and ZnO (99.999%) powders calcined at 1000 °C in an Ar atmosphere for 2 h was used as the target. On the other hand, the films deposited in a pure Ar gas environment show low resistivity of about 3×10−4 Ω cm, comparable to that of indium tin oxide films (10−4 Ω cm). After heat treatment at 650 °C in vacuum, it was found that the films deposited in a mixed gas atmosphere revealed low resistivity similar to that of films deposited in a pure Ar gas. For these annealed films, their electrical properties are very stable when treated at temperatures up to 500 °C in air or 650 °C in vacuum. Also, it is found that the optical band gap of In2O3–ZnO films increase (or decrease) after the heat treatment in vacuum (or O2 atmosphere). These effects are mainly due to the change in carrier concentration before and after heat treatment.