Effect of annealing on structural and optical properties of indium sulfide thin layers produced by chemical bath deposit
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ORIGINAL PAPER
Effect of annealing on structural and optical properties of indium sulfide thin layers produced by chemical bath deposition method M Nasiri Sarvi1, P Esmaili2* and S Asgary3 1
School of New Technologies, Iran University of Science and Technology (IUST), Narmak, Tehran 16846, Iran 2
Young Researchers and Elite Club, Islamic Azad University, Urmia Branch, Urmia, Iran 3
Department of Physics, West Tehran Branch, Islamic Azad University, Tehran, Iran Received: 22 February 2019 / Accepted: 26 July 2019
Abstract: Indium sulfide thin films were prepared by chemical bath deposition method on glass substrates for about 40 min as deposition time and 60 °C as deposition temperature. The films were post-annealed at different temperatures such as 100 °C, 200 °C, 300 °C and 400 °C, for about 1 h. Structural and optical properties of In2S3 thin films after postannealing process have been investigated. The crystallinity and nanostructures of the films were studied by using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and atomic force microscopy analysis. Optical reflectance and transmittance of layers were measured in the wavelength of 300–1100 nm by spectrophotometer instrument. Kramers–Kronig relations were used to calculate the optical constants. The X-ray diffraction measurements showed transformation of an amorphous nature to a crystalline structure by increasing the annealing temperature. The atomic force microscopy images showed by increasing the annealing temperature, the roughness of the thin films increased. The scanning electron microscopy images revealed that growth rate increased consistently with the increase in annealing temperature and well-dispersed quasi-spherical nanoparticles with high agglomeration rate are formed at 400 °C. The energy-dispersive X-ray spectroscopy results show reduction in the S/In ratio from 1.61 to 1.49 when annealing temperature increased. Optical results showed the highest optical band gap of 3.65 eV was achieved at the highest annealing temperature (400 °C). Keywords: Indium sulfide; Optical properties; Structural properties; Kramers–Kronig relations PACS Nos.: 78.20.-e
1. Introduction Indium sulfide (In2S3) is an III–VI semiconductor material with an n-type electrical conductivity. This semiconductor has a direct and large band gap that can be varied from 2 to 3.25 eV [1–3] by the addition of some elements such as oxygen or Na. Because of its good photoconductive properties, high transparency in the visible spectral region and chemical stability, In2S3 was appeared to be suitable to use in photovoltaic industries, optoelectronic and photoelectron chemical solar cell devices [4]. The electrical and optical properties of a b-In2S3 single crystal are stable at normal temperatures, and its band gap energy is about 1.98 eV [5].
*Corresponding author, E-mail: [email protected]
In2S3 can exist in several polymorphs; thus, it is expected that the physical properties of In2S3 films significantly are dependent on the prepar
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