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Parametric optical property database for CdSe1-xSx alloys
Maxwell M. Junda,Corey R. Grice,Yanfa Yan,Nikolas J. Podraza 대한금속·재료학회 2019 ELECTRONIC MATERIALS LETTERS Vol.15 No.4
A comprehensive database of the optical response in the form of complex dielectric function (ε) spectra of magnetron cosputteredCdSe1−xSx alloy thin films is developed spanning the full 0 ≤ x ≤ 1 range of compositions. A parametric modelis presented and used to determine ε describing each film while in both as-deposited and thermally annealed states. Thismodel combines a critical point electronic transition lineshape and an Urbach tail in the above- and below-bandgap portionsof the measured spectrum, respectively, while maintaining first derivative continuity. Additionally, this hybrid parametricdescription of ε automatically determines the Urbach energy (EU) describing the width of the sub-bandgap absorption tail,thereby providing a relative measure of the defect density of the modeled material. These as-deposited CdSe1−xSx films aregenerally found to be the most defective at intermediate compositions with some EU reaching energies > 200 meV. Annealingreduces EU in all films to a relatively uniform value < 100 meV for all compositions. Leveraging the full ε database inmodeling CdS-CdSe bi-layer stacks is demonstrated to be effective in detecting the composition gradients resulting frominter-diffusion upon annealing. The accuracy of this technique is verified through excellent agreement with cross sectionalenergy dispersive X-ray spectroscopy measurements.
Shet, Sudhakar,Ahn, Kwang-Soon,Deutsch, Todd,Wang, Heli,Ravindra, Nuggehalli,Yan, Yanfa,Turner, John,Al-Jassim, Mowafak Cambridge University Press (Materials Research Soc 2010 Journal of materials research Vol.25 No.1
<P>ZnO thin films with significantly reduced band gaps were synthesized by doping N and codoping Al and N at 100 °C. All the films were synthesized by radiofrequency magnetron sputtering on F-doped tin-oxide-coated glass. We found that codoped ZnO:(Al,N) thin films exhibited significantly enhanced crystallinity compared with ZnO doped solely with N, ZnO:N, at the same growth conditions. Furthermore, annealed ZnO:(Al,N) thin films exhibited enhanced N incorporation over ZnO:N films. As a result, ZnO:(Al,N) films exhibited better photocurrents than ZnO:N films grown with pure N doping, suggesting that charge-compensated donor-acceptor codoping could be a potential method for band gap reduction of wide-band gap oxide materials to improve their photoelectrochemical performance.</P>
Improved current collection in WO<sub>3</sub>:Mo/WO<sub>3</sub> bilayer photoelectrodes
Gaillard, Nicolas,Cole, Brian,Kaneshiro, Jess,Miller, Eric L.,Marsen, Bjorn,Weinhardt, Lothar,Bä,r, Marcus,Heske, Clemens,Ahn, Kwang-Soon,Yan, Yanfa,Al-Jassim, Mowafak M. Cambridge University Press (Materials Research Soc 2010 Journal of materials research Vol.25 No.1
<P>We report on the incorporation of molybdenum into tungsten oxide by co-sputtering and its effect on solar-powered photoelectrochemical (PEC) water splitting. Our study shows that Mo incorporation in the bulk of the film (WO3:Mo) results in poor PEC performance when compared with pure WO3, most likely due to defects that trap photo-generated charge carriers. However, when a WO3:Mo/WO3 bilayer electrode is used, a 20% increase of the photocurrent density at 1.6 V versus saturated calomel reference electrode is observed compared with pure WO3. Morphological and microstructural analysis of the WO3:Mo/WO3 bilayer structure reveals that it is formed by coherent growth of the WO3:Mo top layer on the WO3 bottom layer. This effect allows an optimization of the electronic surface structure of the electrode while maintaining good crystallographic properties in the bulk.</P>