Strong inter-conduction-band absorption in heavily fluorine doped tin oxide
2008 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 255, no 5, 1874-1879 p.Article in journal (Refereed) Published
The optical, electrical and structural properties of thin. film tin oxide (TO), F-doped tin oxide (FTO; n(F) approximate to 6 x 10(20) cm (3)) and highly F-doped tin oxide (hFTO; n(F) approximate to 10 x 10(20) cm (3)), grown by spray pyrolysis technique, are studied by atomic force microscopy, Hall effect, X-ray. fluorescence and transmission/reflection measurements. The resistivity (rho = 32 x 10 (4) Omega cm for intrinsic tin oxide) shows intriguing characteristics when F concentration n(F) is increased (rho = 6 x 10 (4) Omega cm for FTO but 25 x 10 (4) Omega cm for hFTO) whereas the carrier concentration is almost constant at high F concentration (n(c) approximate to 6 x 10(20) cm (3) for FTO and hFTO). Thus, F seems to act both as a donor and a compensating acceptor in hFTO. The high carrier concentration has a strong effect on the optical band-edge absorption. Whereas intrinsic TO has room-temperature band-gap energy of E-g approximate to 3.2 eV with an onset to absorption at about 3.8 eV, the highly doped FTO and hFTO samples show relatively strong absorption at 2-3 eV. Theoretical analysis based on density functional calculations of FTO reveals that this is not a defect state within the band-gap region, but instead a consequence of a hybridization of the F donor states with the host conduction band in combination with a band. filling of the lowest conduction band by the free carriers. This allows photon-assisted inter-conduction band transitions of the free electrons to energetically higher and empty conduction bands, producing the below-gap absorption peak.
Place, publisher, year, edition, pages
2008. Vol. 255, no 5, 1874-1879 p.
Tin oxide, Transparent conducting film, Doping, Optical absorption, Resistivity
Other Engineering and Technologies not elsewhere specified
IdentifiersURN: urn:nbn:se:kth:diva-26005DOI: 10.1016/j.apsusc.2008.06.113ISI: 000261274100039ScopusID: 2-s2.0-56949095313OAI: oai:DiVA.org:kth-26005DiVA: diva2:362249
QC 20101109 Uppdaterad från submitted till published 20101109.2010-11-092010-11-092010-11-09Bibliographically approved