Electronic and optical properties of nanocrystalline WO3 thin films studied by optical spectroscopy and density functional calculations
2013 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 20, 205502- p.Article in journal (Refereed) Published
The optical and electronic properties of nanocrystalline WO3 thin films prepared by reactive dc magnetron sputtering at different total pressures (P-tot) were studied by optical spectroscopy and density functional theory (DFT) calculations. Monoclinic films prepared at low P-tot show absorption in the near infrared due to polarons, which is attributed to a strained film structure. Analysis of the optical data yields band-gap energies E-g approximate to 3.1 eV, which increase with increasing P-tot by 0.1 eV, and correlate with the structural modifications of the films. The electronic structures of triclinic delta-WO3, and monoclinic gamma- and epsilon-WO3 were calculated using the Green function with screened Coulomb interaction (GW approach), and the local density approximation. The delta-WO3 and gamma-WO3 phases are found to have very similar electronic properties, with weak dispersion of the valence and conduction bands, consistent with a direct band-gap. Analysis of the joint density of states shows that the optical absorption around the band edge is composed of contributions from forbidden transitions (andgt;3 eV) and allowed transitions (andgt;3.8 eV). The calculations show that E-g in epsilon-WO3 is higher than in the delta-WO3 and gamma-WO3 phases, which provides an explanation for the P-tot dependence of the optical data.
Place, publisher, year, edition, pages
Institute of Physics: Hybrid Open Access , 2013. Vol. 25, no 20, 205502- p.
Engineering and Technology
IdentifiersURN: urn:nbn:se:liu:diva-93962DOI: 10.1088/0953-8984/25/20/205502ISI: 000318556100013OAI: oai:DiVA.org:liu-93962DiVA: diva2:628287
Funding Agencies|Swedish Energy Agency||Swedish Research Council||European EM ECW program EUBRANEX||computers center HPC2N||computers center NSC through SNIC/SNAC||computers center NSC through MATTER||2013-06-132013-06-132014-08-28Bibliographically approved