Optoelectronic study and annealing stability of room temperature pulsed laser ablated ZnSe polycrystalline thin films Taj Muhammad Khan n , M. Zakria, Mushtaq Ahmad, Rana I. Shakoor National Institute of Laser and Optronics (NILOP), P.O. Nilore, 45650 Islamabad, Pakistan article info Article history: Received 18 June 2013 Received in revised form 24 October 2013 Accepted 25 October 2013 Available online 8 November 2013 Keywords: Zinc selenide Photoluminescence Pulsed laser deposition Raman spectroscopy XRD abstract In principal, we described stability of the room temperature ZnSe thin films with thermal annealing deposited onto glass by pulsed laser deposition technique using third harmonic 355 nm of Nd: YAG laser beam. Optoelectronic analysis and stability with thermal annealing was described in terms of structural and optical properties. These properties were investigated via X-ray diffraction, atomic force microscope, scanning electron microscope, Raman, Fourier transform infrared and photoluminescence spectro- scopies. From the strong reflection corresponding to the (1 1 1) plane (2θ ¼27.481) and the longitudinal optical “LO” phonon modes at 250 cm 1 and 500 cm 1 in the X-ray diffraction and Raman spectra, a polycrystalline zincblende structure of the film was established. At 300 and 350 1C annealing temperatures, the film crystallites were preferentially oriented with the (1 1 1) plane parallel to the substrate and became amorphous at 400 1C. Atomic force microscopic images showed that the morphologies of ZnSe films became smooth with root mean squared roughness 9.86 nm after annealing at 300 and 350 1C while a rougher surface was observed for the amorphous film at 400 1C. Fourier transform infrared study illustrated the chemical nature and Zn–Se bonding in the deposited films. For the as-deposited and annealed samples at 300 and 350 1C, scanning electron micrographs revealed mono-dispersed indistinguishable ZnSe grains and smooth morphological structure which changed to a cracking and bumpy surface after annealing at 400 1C. The physical phenomenon of annealing induced morphological changes could be explained in terms of “structure zone model”. Excitonic emission at 456 nm was observed for both as-deposited and annealed film at 350 1C. The transmission spectrum shows oscillatory behavior because of the thin film interference and exhibited a high degree of transparency down to a wavelength 500 nm in the IR region. Energy band-gap was increased from 2.65 eV to 2.7 eV for the annealed crystalline film at 350 1C which was further decreased to 2.56 eV for the annealed amorphous film at 400 1C. The observed results manifested that room temperature pulsed laser ablated ZnSe thin film showed excellent structural, optical and morphological stability up 350 1C for optoelectronic applications. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Zinc selenide (ZnSe) is an important optoelectronic semicon- ducting material with a direct wide band-gap 2.7 eV at room temperature [1]. ZnSe is technologically important, because it can be prepared in both n- and p-type forms. Thin films of this material are used extensively in the optoelectronic industry for their high optical transmittance (  90%) in the visible region and reflectance in the infrared (IR) region [1,2]. Moreover, it has been widely utilized as an essential part of many optoelectronic devices like: transparent electrodes in flat-panel displays and solar cells; transparent heating elements for automobile and aircraft windows; and transparent heat reflecting window material for buildings, lamps, solar collectors, gas sensors and antireflection coatings [2,3]. While to improve structural and optical properties of this material in thin film technology for the applications like blue to UV light emitting diodes (LED), UV laser, UV detectors, etc. [4,5], the deposition procedure is followed by a controlled anneal- ing in suitable environment. Thermal stability of the films is an important characteristic usually depends on type of substrate, annealing temperature and other deposition conditions, para- meters and have been reported in the literature for high substrate temperature [6]. Nevertheless, thermal stability of room tempera- ture pulse laser ablated ZnSe thin film on glass substrate is less reported even though it is technologically more significant. ZnSe thin films have been deposited by a number of deposition techniques such as thermal evaporation, molecular beam epitaxy (MBE), RF/DC magnetron sputtering (MS), atomic layer deposition Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence 0022-2313/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jlumin.2013.10.064 n Corresponding author. Tel.: þ92 519248671-6x3053; fax: þ92 512208051. E-mail address: tajakashne@gmail.com (T.M. Khan). Journal of Luminescence 147 (2014) 97–106