Metastable Rhombohedral Phase Transition of Semiconducting Indium Oxide Controlled by Thermal Atomic Layer Deposition

Indium oxide (In2O3) thin films were deposited via thermal atomic layer deposition (ALD) to exploit their potential as semiconductors in thin-film transistors (TFTs), using a new liquid type indium complex precursor (In­(CH3)3[CH3OCH2CH2NHtBu]). In2O3 films were deposited successfully at lower temperatures and exhibited a satisfactory growth rate (∼0.35 Å per cycle). In addition, we investigated the effect of deposition temperature from 100 to 250 °C on the microstructure and chemical and physical properties of In2O3 films. Interestingly, the In2O3 film had a clear rhombohedral structure at deposition temperatures from 100 to 150 °C. For the 200 and 250 °C deposition temperatures, the phase of In2O3 transformed to a cubic structure. The crystalline structure of the In2O3 film was extremely sensitive to deposition temperatures, giving rise to a wide range of tunable physical and electrical properties. Based on a comparison of comprehensive structural transmission electron microscopy analysis, density functional theory calculations, and systematic experimental measurements, we explored the possibility of TFTs with an ALD-processed In2O3 layer as a semiconductor.