Atomic Layer Deposition of Ternary Indium/Tin/Aluminum Oxide Thin Films,Their Characterization and Transistor Performance under Illumination.

Multilayered heterostructures comprising of In₂O₃, SnO₂, and Al₂O₃ were studied for their application in thin-film transistors (TFT). The compositional influence of tin oxide on the properties of the thin-film, as well as on the TFT characteristics is investigated. The heterostructures are fabricated by atomic layer deposition (ALD) at 200 °C, employing trimethylindium (TMI), tetrakis(dimethylamino)tin (TDMASn), trimethylaluminum (TMA), and water as precursors. After post-deposition annealing at 400 °C the thin-films are found to be amorphous, however, they show a discrete layer structure of the individual oxides of uniform film thickness and high optical transparency in the visible region. Incorporation of only two monolayers of Al₂O₃ in the active semiconducting layer the formation of oxygen vacancies can be effectively suppressed, resulting in an improved semiconducting and switching behavior. The heterostacks comprising of In₂O₃/SnO₂/Al₂O₃ are incorporated into TFT devices, exhibiting a saturation field-effect mobility (μ_sat) of 2.0 cm² ⋅ V⁻¹ s⁻¹, a threshold-voltage (V_th) of 8.6 V, a high current on/off ratio (I_On/I_Off) of 1.0×10⁷, and a subthreshold swing (SS) of 485 mV ⋅ dec⁻¹. The stability of the TFT under illumination is also altered to a significant extent. A change in the transfer characteristic towards conductive behavior is evident when illuminated with light of an energy of 3.1 eV (400 nm).