Regensburg 2013 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 35: Application of Thin Films
DS 35.7: Vortrag
Freitag, 15. März 2013, 11:00–11:15, H8
Chemical purity in high performance solution processed zinc oxide TFTs — •Marlis Ortel, Torsten Balster, and Veit Wagner — Research Center for Functional Materials and Nanomolecular Science, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany
Conversion of precursor materials in solution processed semiconductor plays an important role in device application. The organic by-products from zinc acetate conversion into ZnO have a significant influence on the electronic structure of the resulting semiconductor layer. They can significantly influence charge transport in the material. Hence the impact of deposition and post-deposition annealing on the chemical composition of the ZnO semiconductor was investigated by means of x-ray photoelectron spectroscopy (XPS), optical and electrical measurements in a wide process temperature range from 200∘C to 500∘C.
It was found, that the increase in deposition temperature from 360∘C to 500∘C leads to a reduction in carbon content by 30% and an increase of the oxygen to zinc ratio from 0.82 to 0.96. These XPS results correspond well with optical measurements, which exhibit a blue-shift of the optical band gap by 20 meV to a value of 3.19 eV reflecting an improved layer quality. The layers were electrically analyzed in a field-effect transistor geometry. The optimization in the purity of the ZnO semiconductor by thermal treatment lead to an improvement of the field-effect mobility up to 13cm2V−1s−1. The increase in mobility is found to be correlated to an on-set voltage shift from 14V to an ideal value of 0V, which reflects a reduction in the level of deep traps.