Abstract
In this paper, zinc sulfide nanoparticle (ZnS-NP) thin films were deposited onto glass substrates by chemical bath deposition using zinc sulfate as the cation precursor and thiourea as the anionic precursor. Different bath temperatures (65, 70, 75, and 80°C) and different deposition times (20, 30, 40, and 50 min) were selected to study the performance of ZnS thin films. Topographical and optical characterizations of the films were studied using the atomic force microscope (AFM) and UV-Vis spectroscope. The best ZnS thin films were deposited at a bath temperature (70°C) and a deposition time (30 min) with homogeneous distribution, high density, and small average diameter (106 nm). The energy gap (Eg) was found to be in the range of 4.05-3.97 eV for the ZnS films. Optical constants (refractive index, n, extinction coefficient, k, and dielectric constant, ε) of the films were obtained in the wavelength range 300-500 nm by using spectrophotometric measurement. The dispersion of the refractive index is analyzed by using a single oscillator model. The oscillator energy E0 and dispersion energy Ed were determined using the Wemple-DiDomenico single oscillator model. Urbach’s energy increases from 0.907 eV to 2.422 eV with increasing of deposition time. The calculated radius of nanoparticles using Brus equation was 1.9, 2.3, 2.45, and 2.51 nm at deposition times 20, 30, 40, and 50 min, respectively.
Highlights
Zinc sulfide is one of the most important II-VI semiconductor materials due to its distinct electrical and optical properties
At lower deposition time td = 20 min, spherical zinc sulfide nanoparticle (ZnS-NP) with different sizes and unequal distribution formed on the surface of the film, while the particles carpet the substrate at deposition time 30 min with high density and uniform spherical shape
Comparing atomic force microscope (AFM) images at different immersing times, we find that deposition time 30 min is the most suitable time to form ZnS-NPs with a small diameter and uniform spherical shapes
Summary
Zinc sulfide is one of the most important II-VI semiconductor materials due to its distinct electrical and optical properties. Zinc sulfide nanoparticles (ZnS-NPs) with wide bandgap (3.5-3.8 eV) have recently received intensive attention to be used in many applications [1] such as antimicrobial activity [2, 3], electroluminescence devices, photonic devices [4], field emission devices [5], sensors [6, 7], and applications in infrared windows [8] and lasers [9, 10]. The main goal of this present work is to study the influence of bath temperature and time of deposition on surface topography and optical properties of ZnS-NP thin films.
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