Atomic-Layer-Deposition of Indium Oxide Nano-films for Thin-Film Transistors

Atomic-layer-deposition (ALD) of In₂O₃ nano-films has been investigated using cyclopentadienyl indium (InCp) and hydrogen peroxide (H₂O₂) as precursors. The In₂O₃ films can be deposited preferentially at relatively low temperatures of 160-200 °C, exhibiting a stable growth rate of 1.4-1.5 Å/cycle. The surface roughness of the deposited film increases gradually with deposition temperature, which is attributed to the enhanced crystallization of the film at a higher deposition temperature. As the deposition temperature increases from 150 to 200 °C, the optical band gap (E_g) of the deposited film rises from 3.42 to 3.75 eV. In addition, with the increase of deposition temperature, the atomic ratio of In to O in the as-deposited film gradually shifts towards that in the stoichiometric In₂O₃, and the carbon content also reduces by degrees. For 200 °C deposition temperature, the deposited film exhibits an In:O ratio of 1:1.36 and no carbon incorporation. Further, high-performance In₂O₃ thin-film transistors with an Al₂O₃ gate dielectric were achieved by post-annealing in air at 300 °C for appropriate time, demonstrating a field-effect mobility of 7.8 cm²/V⋅s, a subthreshold swing of 0.32 V/dec, and an on/off current ratio of 10⁷. This was ascribed to passivation of oxygen vacancies in the device channel.