Zinc Oxysulfide Thin Films Grown by Pulsed Laser Deposition
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Pulsed laser deposition was used to produce thin films of zinc oxysulfide (ZnO x S1−x ) on quartz substrates. The target was a sintered pellet (ZnO0.39S0.61) made of a solution precipitate. The film composition obtained by electron probe microanalysis (EPMA) was ZnO0.41S0.59, ZnO0.44S0.56, and ZnO0.37S0.63 for substrate temperatures of 450°C, 540°C, and 630°C, respectively. X-ray diffraction (XRD) showed that samples deposited at 450°C and at 540°C had a prominent cubic sphalerite phase, whereas samples deposited at 630°C consisted of three phases, viz. hexagonal wurtzite and cubic sphalerite (ZnS), and hexagonal zincite (ZnO). With respect to the tabulated lattice spacings for sphalerite (cell constant 0.5406 nm), distinct shifts were observed for the low temperature samples, yielding cell constants around 0.533 nm. Transmission electron microscopy (TEM)–selected area electron diffraction studies support the XRD data. Patterns of films deposited at 540°C could be indexed as sphalerite, with similar lattice shifts as in XRD, resulting in a cell constant of 0.53. Locally highly resolved chemical analysis by TEM–energy dispersive x-ray analysis revealed a stoichiometry that was consistent with the EPMA results. Ultraviolet (UV)–visible transmission measurements of the films led to bandgap energies around 3.3 eV, which is well below the reported bandgap energies of ZnS.
Key wordsZinc oxysulfide pulsed laser deposition thin films
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S.H.D. would like to thank Prof. Pratap Raychaudhuri, Department of Condensed Matter Physics and Material Sciences, Tata Institute of Fundamental Research (TIFR), Mumbai, India, for making available the PLD facility and Mr. John Abraham for his help in carrying out the depositions. S.H.D. would also like to thank Prof. Deepa Khushlani of TIFR for her permission to use her laboratory facilities and for the immense moral support.
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