title: Electronic Structure of Low-Temperature Solution-Processed Amorphous Metal Oxide Semiconductors for Thin-Film Transistor Applications.
abstract: The electronic structure of low temperature, solution-processed indium-zinc oxide thin-film transistors is complex and remains insufficiently understood. As commonly observed, high device performance with mobility >1 cm2V-1s-1is achievable after annealing in air above typically 250 °C but performance decreases rapidly when annealing temperatures ≤200 °C are used. Here, the electronic structure of low temperature, solution-processed oxide thin films as a function of annealing temperature and environment using a combination of X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and photothermal deflection spectroscopy is investigated. The drop-off in performance at temperatures ≤200 °C to incomplete conversion of metal hydroxide species into the fully coordinated oxide is attributed. The effect of an additional vacuum annealing step, which is beneficial if performed for short times at low temperatures, but leads to catastrophic device failure if performed at too high temperatures or for too long is also investigated. Evidence is found that during vacuum annealing, the workfunction increases and a large concentration of sub-bandgap defect states (re)appears. These results demonstrate that good devices can only be achieved in low temperature, solution-processed oxides if a significant concentration of acceptor states below the conduction band minimum is compensated or passivated by shallow hydrogen and oxygen vacancy-induced donor levels.
authors.affiliation: Cavendish Laboratory 19 JJ Thomson Avenue, CB3 OHE, Cambridge, UK.
authors.forename: Josephine
authors.initials: J
authors.lastname: Socratous
authors.affiliation: Cavendish Laboratory 19 JJ Thomson Avenue, CB3 OHE, Cambridge, UK.
authors.forename: Kulbinder K
authors.initials: KK
authors.lastname: Banger
authors.affiliation: Cavendish Laboratory 19 JJ Thomson Avenue, CB3 OHE, Cambridge, UK.
authors.forename: Yana
authors.initials: Y
authors.lastname: Vaynzof
authors.affiliation: Cavendish Laboratory 19 JJ Thomson Avenue, CB3 OHE, Cambridge, UK.
authors.forename: Aditya
authors.initials: A
authors.lastname: Sadhanala
authors.affiliation: Cavendish Laboratory 19 JJ Thomson Avenue, CB3 OHE, Cambridge, UK.
authors.forename: Adam D
authors.initials: AD
authors.lastname: Brown
authors.affiliation: Cavendish Laboratory 19 JJ Thomson Avenue, CB3 OHE, Cambridge, UK.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Sepe
authors.affiliation: Cavendish Laboratory 19 JJ Thomson Avenue, CB3 OHE, Cambridge, UK.
authors.forename: Ullrich
authors.initials: U
authors.lastname: Steiner
authors.affiliation: Cavendish Laboratory 19 JJ Thomson Avenue, CB3 OHE, Cambridge, UK.
authors.forename: Henning
authors.initials: H
authors.lastname: Sirringhaus
keywords: indium–zinc oxide; nitrates; solution-processing; spectroscopy; subgap density of states