Structure-Charge Transport Relationships in Fluoride-Doped Amorphous Semiconducting Indium Oxide: Combined Experimental and Theoretical Analysis


Anion doping of transparent amorphous metal oxide (a-MO) semiconductors is virtually unexplored but offers the possibility of creating unique optoelectronic materials owing to the chemical tuning, modified crystal structures, and unusual charge-transport properties that added anions may impart. We report here the effects of fluoride (F-) doping by combustion synthesis, in an archetypical metal oxide semiconductor, indium oxide (In-O). Optimized fluoride-doped In-O (F:In-O) thin films are characterized in depth by grazing incidence X-ray diffraction, X-ray reflectivity, atomic force microscopy, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure (EXAFS). Charge-transport properties are investigated in thin-film transistors (TFTs), revealing that increasing fluoride content (0.0 → 1.57 atom %) slightly lowers the on-current (Ion) and electron mobility due to scattering from loosely bound F- centers but enhances important TFT performance parameters such as the Ionn/Ioff ratio, subthreshold swing, and bias stress stability, yielding superior TFT switching versus undoped In-O. These results are convincingly explained by ab initio molecular dynamics simulations and density functional theory electronic structure calculations. Combined with the EXAFS data, the experimental and theoretical results show that F- hinders crystallization by enhancing the local and medium-range disorder, promotes a uniform film morphology, and favors the formation of deeper, more localized trap states as compared to F--free In-O. These data also show that the local organization and electronic structure of amorphous F--doped oxide semiconductors are significantly different from those of F--doped crystalline oxide semiconductors and suggest new avenues to further modify a-MOs for enhanced optoelectronic properties.




The authors thank the Northwestern Univ. (NU) MRSEC Grant No. NSF-DMR 1720139 for support of this research.

Keywords and Phrases

Atomic force microscopy; Calculations; Carrier transport; Combustion synthesis; Crystal atomic structure; Density functional theory; Electronic structure; Extended X ray absorption fine structure spectroscopy; Fluorine compounds; Metals; Molecular dynamics; Morphology; MOS devices; Negative ions; Optoelectronic devices; Oxide semiconductors; Semiconducting indium; Semiconductor doping; Silicon on insulator technology; Synthesis (chemical); Thin film transistors; Thin films; Transport properties; X ray absorption; X ray photoelectron spectroscopy, Ab initio molecular dynamics simulation; Electronic structure calculations; Extended X-ray absorption fine structures; Grazing incidence X-ray diffraction; Metal oxide semiconductor; Opto-electronic materials; Optoelectronic properties; Thin-film transistor (TFTs), Indium compounds

International Standard Serial Number (ISSN)

0897-4756; 1520-5002

Document Type

Article - Journal

Document Version


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© 2020 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Jan 2020