Band-edge modification and mid-infrared absorption of co-deposited FexZn1-xS thin films

Nelly-Ann Molland, Zahra Ghadyani, Eric A. Karhu, Stefano Poggio, Mohammadreza Nematollahi, Morten Kildemo, Turid W. Reenaas, Joseph J. BelBruno, Ursula J. Gibson

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    The bandgap of iron-doped ZnS has been reported by others to change significantly under the addition of a few atomic percent of iron, which would have significant implications for solar energy. Here, thin films of FexZn1-xS with x = 0 to 0.24 were made by co-deposition of Fe and ZnS using thermal evaporation. In contrast to results on nanoparticles and electrodeposited materials, all co-deposited films had optical properties consistent with a direct bandgap of ~3-3.5 eV. The absorption peak at 2.7 µm from substitutional Fe2+ in the ZnS films was well isolated up to concentrations of over 2% (~1021cm−3), despite the small crystallite size, suggesting the films may have applications as mid-infrared saturable absorbers. Increasing dopant concentration resulted in band edge softening. Density functional calculations are presented and are consistent with our observations of the Fe:ZnS films, demonstrating spin-polarized midgap states and additional states at the band edge.
    Original languageEnglish
    Pages (from-to)1613-1620
    Number of pages1
    JournalOptical materials express
    Issue number7
    Publication statusPublished - 2015


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