Optical investigation on zinc doped cadmium sulphide nanocrystalline thin films J.R. Jayaramaiah a, * , R. Shamanth b , V. Jayanth c , K.S. Shamala d a Department of Physics, Government First Grade College, Nargund 582 207, India b Department of ECE, Vijaya Vittala Institute of Technology, Bangalore 560 077, India c Department of Mechanical Engineering, Siddaganga Institute of Technology, Tumkur 572 103, India d Department of Physics, Mount Carmel College (Autonomous), Bangalore 560 052, India article info Article history: Received 8 November 2015 Received in revised form 27 January 2016 Accepted 15 April 2016 Available online 26 April 2016 Keywords: Thin films Crystal structure Nano structured materials X-ray diffraction Optical materials abstract Optical investigation on blue shift behavior of zinc doped cadmium sulphide nano-crystalline thin films have been prepared by spray pyrolysis method at 375 ± 10  C. The crystallinity and phase have been characterized by glancing angle X-ray diffraction. The XRD peaks confirm the hexagonal structure of cadmium sulphide. The crystallites sizes are found its range of 15e20 nm. The surface morphology is analyzed by using field emission scanning electron microscopy. The morphology of the film is seen as uniform distribution of homogeneous fine solid grains which are compact in nature. Optical absorption spectrum reveals an absorption peak at 475 nm. Indicating that blue shift due to quantum confinement effect, as a result the direct energy gap is increased and found its value is 2.91 eV. Raman spectrum reveals the longitudinal optical phonon peaks are at 302 cm 1 and 603 cm 1 . The noticeable asymmetry and frequency shift confirm the decrease in particle size. X-ray photoelectron spectroscopy reveals the surface composition and binding energy of elements and it confirm the presence of zinc. The photo- luminescence spectrum reveals an emission peak at 728 nm is analyzed. Zn doped cadmium sulphide thin film is useful for window material in solar cells and luminescent red phosphor. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Nowadays a line of research is focus towards the nano-science. Nanostructure materials attract for physical, chemical, optical and electrical properties, which are diverse from their bulk counter parts [1]. Significant and innovative physical and chemical prop- erties are generated at nano-scale thin films due to the quantum confinement effect [2]. Quantum dot solar cells are promising sensitizing devices for photovoltaic applications in solar energy conversion [3]. The world is suffering from a serious pollution and future deplete of fossil fuels. Solar radiation is considered as one of the most abundant supply of free energy in nature. The solar energy is one of the hopeful solutions for the global energy crisis. Thus, solar cells have been extensively studied in order to increase the effi- ciency, and reduce the cost of converting solar energy into elec- tricity. The thin film solar cells open up an exceptional potential in cost reduction. Polycrystalline nature of cadmium sulphide (CdS) thin film solar cells are the reason for low cost and high conversion efficiency [4]. Hexagonal wurtzite structure of bulk CdS has a melting point of 1600  C and band gap energy is 2.42 eV at room temperature. Its refractive index is 2.52 at wavelength 600 nm. It has three phases in size reduction viz. wurtzite, zinc blend and rock salt. Wurtzite is the most stable phase and also easy to synthesize. Wurtzite phase is seen both in bulk and nano-scale, but not in cubic and rock salt phase. It exhibits size dependent behavior, at size 2.5 nm it has melting point ~400  C. The phase changes from wurtzite to rock salt cubic phase at a very high pressure [5e13]. CdS nano films exhibits structural, electronic, optical, luminescence and photo conducting properties, which deviate from their bulk [14,15]. The probable application prospects are in photo detectors, LASER, LED, phosphor, sensors, address decoders, high density magnetic information storage and others [16]. The politenesses of ternary compounds have been much more attractive for the alteration of the band gap and the lattice parameters. In formation of solar cell a low dimension window layer material is necessary to avoid high cur- rent loss. High efficiency devices require a thin film window layer to * Corresponding author. E-mail address: jaygubbi@rediffmail.com (J.R. Jayaramaiah). Contents lists available at ScienceDirect Current Applied Physics journal homepage: www.elsevier.com/locate/cap http://dx.doi.org/10.1016/j.cap.2016.04.011 1567-1739/© 2016 Elsevier B.V. All rights reserved. Current Applied Physics 16 (2016) 799e804