Self‐Compensation in Transparent Conducting F‐Doped SnO2

• Published in: Advanced functional materials 2018-01, Vol.28 (4), p.n/a
• Main Authors: Swallow, Jack E. N., Williamson, Benjamin A. D., Whittles, Thomas J., Birkett, Max, Featherstone, Thomas J., Peng, Nianhua, Abbott, Alex, Farnworth, Mark, Cheetham, Kieran J., Warren, Paul, Scanlon, David O., Dhanak, Vin R., Veal, Tim D.
• Format: Article
• Language: English
• Subjects: Atmospheric models; carrier transport; Chemical vapor deposition; Compensation; Defects; Density functional theory; Electromagnetism; Fluorine; fluorine‐doped stannic oxide; fluorine‐doped tin dioxide; fluorine‐doped tin oxide; Hall effect; Impurities; Interstitials; Mass spectrometry; Materials science; Photoelectric emission; Photoelectron spectroscopy; Quantitative analysis; Secondary ion mass spectrometry; Self compensation; Tin dioxide; Transport properties
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201701900

The factors limiting the conductivity of fluorine‐doped tin dioxide (FTO) produced via atmospheric pressure chemical vapor deposition are investigated. Modeling of the transport properties indicates that the measured Hall effect mobilities are far below the theoretical ionized impurity scattering limit. Significant compensation of donors by acceptors is present with a compensation ratio of 0.5, indicating that for every two donors there is approximately one acceptor. Hybrid density functional theory calculations of defect and impurity formation energies indicate the most probable acceptor‐type defects. The fluorine interstitial defect has the lowest formation energy in the degenerate regime of FTO. Fluorine interstitials act as singly charged acceptors at the high Fermi levels corresponding to degenerately n‐type films. X‐ray photoemission spectroscopy of the fluorine impurities is consistent with the presence of substitutional FO donors and interstitial Fi in a roughly 2:1 ratio in agreement with the compensation ratio indicated by the transport modeling. Quantitative analysis through Hall effect, X‐ray photoemission spectroscopy, and calibrated secondary ion mass spectrometry further supports the presence of compensating fluorine‐related defects. Compensating acceptor defects dramatically reduce electronic performance of F:SnO2 transparent conductor grown by chemical vapor deposition. Electron carrier mobilities are seen to be greatly diminished from the theoretically predicted optimum. Using hybrid density functional theory calculations and experimental methods, and analysis, the defect responsible for self‐compensation in F:SnO2 is determined to be the fluorine interstitial.