Transparent and conductive CdS:Ca thin films for optoelectronic applications
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Transparent and conductive CdS:Ca thin films for optoelectronic applications S. Yılmaz1 · İ. Polat2 · M. Tomakin3 · E. Bacaksız4 Received: 16 March 2020 / Accepted: 22 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This paper presents the structural, morphological, optical and electrical evolution of Ca-doped CdS thin films. Non-doped and Ca-doped CdS samples with various amounts of Ca atoms (from 0 to 10 at.% with an increasing step of 2 at.%) were grown by spray pyrolysis route on glass slides. The structural investigation by X-ray diffraction showed that Ca-doping distorted CdS structure until 8 at.% Ca-doping and then a slight improvement in the intensity of (101) peak was obtained for 10 at.% Ca-doping compared to the other Ca-doping samples. Morphological analysis displayed a grain growth for a low amount of Ca-doping whereas higher concentration of Ca-doping led to a reduction in the grain size of CdS thin films. More stoichiometric CdS specimens were obtained after various amounts of Ca-doping according to energy dispersive X-ray spectroscopy data. Transparency of the CdS samples enhanced remarkably with the incorporation of Ca atoms in CdS with a particular concentration of 10 at.%. Tauc’s plot investigation illustrated that the bandgap score of samples changed from 2.54 eV for non-doped CdS to 2.48 eV for 4 at.% Ca-doped CdS thin films. Further increase of Ca-doping doesn’t vary the bandwidth of CdS samples. Photoluminescence data indicated that Ca-doped CdS thin films had lower intrinsic defects compared with non-doped CdS one. The electrical examination demonstrated that the carrier density of CdS thin films increased till 6 at.% Ca-doping and then decreased further increase of Ca-doping. However, resistivity values exhibited the opposite behavior accordingly. In conclusion, it can be pronounced that 6 at.% Ca-doped CdS thin films are the optimum specimen to be used as an effective transparent and conductive material in the optoelectronic devices. Keywords CdS thin films · Ca-doping · Spray pyrolysis · Optical properties · Electrical properties
1 Introduction CdS is one of the semiconducting metal chalcogenides in II–VI group and have lots of superior properties than others such as high stability, moderate band gap score (2.42 eV at 300 K), high transparency and good conductivity. * S. Yılmaz [email protected] 1
Department of Materials Engineering, Faculty of Engineering, Adana Alparslan Türkeş Science and Technology University, 01250 Adana, Turkey
2
Department of Energy Systems Engineering, Faculty of Technology, Karadeniz Technical University, Trabzon, Turkey
3
Department of Physics, Faculty of Arts and Sciences, Recep Tayyip Erdogan University, Rize, Turkey
4
Department of Physics, Faculty of Sciences, Karadeniz Technical University, 61080 Trabzon, Turkey
Additionally, CdS materials have refractive index values in the range of 2.58–2.55 for the wavelength interval of 350–1600 nm, respectively while they possess extinction coefficient values
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