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    Impact of in/ex situ annealing and reaction temperature on structural, optical and electrical properties of SnS thin films
    (Elsevier, 2021) Olgar, M. A.; Ciri, A.; Tomakin, M.; Zan, R.
    In this work, SnS thin films were prepared by in situ and ex situ annealing process of precursor films deposited by RF (Radio Frequency) magnetron sputtering employing binary SnS target. In situ annealing treatment was performed in sputtering chamber and ex situ annealing treatment was performed using RTP (Rapid Thermal Processing) system under Ar+H-2 mix gas employing 225, 300 and 375 degrees C as reaction temperatures in order to find out the best fabrication parameters of SnS thin film since it has been used as an absorber layer in the cell structure. The EDX (Energy Dispersive X-ray Spectroscopy) measurements showed that precursor and reacted films have almost stoichiometric composition except for in situ annealed sample at 375 degrees C. XRD (X-ray Diffraction) patterns of all samples revealed orthorhombic SnS phase regardless of annealing route and temperature. In addition to SnS phase, formation of SnS2 phase was observed in in situ annealed SnS samples at 225 and 300 degrees C. Moreover, in situ annealed samples displayed larger crystallite size and lower micro strain compared to ex situ annealed samples. Raman spectra of the samples confirmed formation of orthorhombic SnS phase and it was also seen that crystalline quality gave rise to shift in position of Raman bands for some samples. Only a SEM (Scanning Electron Microscopy) image of in situ annealed sample at 375 degrees C displayed distinct surface morphology. Optical band gap values of the samples showed variation between 1.35 and 1.66 eV. Electrical characterization of the films showed that resistivity values changed from 3.34x10(3) to 2.28x10(4) Omega-cm and carrier concentration values changed from 1.34x10(14) to 1.05x10(15) cm(-3). It was seen that in situ annealing at 375 degrees C exhibited more promising results for potential SnS based photovoltaic applications. (C) 2021 Elsevier B.V. All rights reserved.
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    Phase transformation in Cu2SnS3 (CTS) thin films through pre-treatment in sulfur atmosphere
    (Springer, 2021) Olgar, M. A.; Basol, B. M.; Tomakin, M.; Bacaksiz, E.
    In this study, Cu2SnS3 (CTS) thin films prepared by a two-step sulfurization process were characterized. Cu and Sn metallic layers were first deposited on glass substrates by sputtering and then annealed in-situ while in the sputtering chamber to obtain CuSn (CT) alloys. This was followed by a pre-treatment step at temperatures between 200 and 350 degrees C in presence of S vapors. Finally, a full sulfurization step was performed at 525 degrees C to obtain the desired CTS phase. CTS films were characterized using EDX, XRD, Raman spectroscopy, SEM, optical transmission and Van der Pauw methods. It was found that all CTS samples had Cu-poor chemical composition. XRD data revealed only diffraction peaks belonging to CTS structure after the full sulfurization step. Raman spectra of the samples showed that except for the CTS sample pre-treated at 250 degrees C (CTS-250), which displayed the tetragonal crystal system, the films were dominated by the monoclinic structure. SEM surface images showed dense and polycrystalline microstructure, CTS-200 sample exhibiting a more uniform morphology. Optical band gap values were found to be ranging from 0.92 to 1.19 eV. All samples showed p-type conductivity but the sample pre-treated at 350 degrees C had higher resistivity and lower carrier concentration values. Overall, the CTS layer prepared using the pre-treatment step at 200 degrees C exhibited more promising structural and optical properties for potential photovoltaic applications. This work demonstrated that it is possible to change the crystal structure of sulfurized CTS thin films through a pre-treatment step.