Optoelectronic properties of n-Ag2S nanotubes/p-Si heterojunction photodetector prepared by chemical bath deposition technique: An effect of deposition time
Introduction
Silver sulfide is a n-type semiconducting material with direct energy gap in the range of (1-2.2) eV at room temperature and it belongs to I–VI compound semiconductors [1,2]. Due to its fascinating photoelectric and thermoelectric properties, Ag2S was used extensively in many applications, for example, photosensitizer, solar cells, photoconductors, gas sensors, superionic conductor, infrared detectors, and resistive switch [3], [4], [5], [6], [7], [8]. It is reported that the morphology and composition are playing a vital role in determining the applications of Ag2S [9]. The morphology of silver sulfide depends on the preparation method and conditions. Various techniques were used to prepare silver sulfide thin films such as chemical vapor deposition CVD, sol-gel, thermal evaporation, hydrothermal, laser ablation, spray pyrolysis, molecular beam epitaxy MBE, chemical bath deposition, etc [10], [11], [12], [13], [14]. Recently, Arulraj et al. prepared high quality stoichiometric Ag2S film on the nickel mesh substrate using CBD technique for energy storage applications [15]. The CBD method for the deposition of thin films from an aqueous solution is a promising technique because of its simplicity, affordability, convenience for large-scale deposition and having easily-controllable parameters such as concentration, pH, deposition temperature and deposition time, etc. The preparation conditions such as solution concentration, pH value, deposition, time and bath temperature are optimized in order to get good quality of semiconductor thin films. The film properties deposited by this technique were depending on the deposition time, solution temperature, substrate type, complex agent type, and pH of the solution [18], [19], [20]. Ag2S has been used effectively as high responsivity quantum dot (QDs) photodetectors in the UV-Vis region. Kang et al. reported on the fabrication and characterization of high photosensitivity quantum dot Ag2S and Li-doped Ag2S photodetectors by sonochemistry method [16]. Chen et al., study the characteristics of wide spectral range Ag2S/ZnO core-shell nano-heterojunction photodetector prepared by chemical method [17]. Photodetectors based silicon heterojunction draw attention due their high responsivity, low concentration of recombination centers, wide spectral range, simplicity, small dark current, and low-cost fabrication. Very few studies have been reported on the fabrication of Ag2S/Si photodetector. Tretyakov et al. [21] reported on the fabrication and characterization of Ag2SQD/Si photodetector prepared by chemical method for the wavelengths ranged from 1 to 1.7µm with noise equivalent1.1 × 10−10 W/ Hz0.5. Herein, we report the fabrication of n-Ag2S/p-Si heterojunction photodetector by chemical bath deposition technique without using buffer layer and/or post annealing. The effect of the deposition time on the optoelectronic properties and figures of merit of the n-Ag2S/p-Si photodetector was demonstrated.
Section snippets
Experimental
The chemicals used for film deposition were of high purity, analytic grade and used without further purification. To deposit Ag2S film, 0.1M of AgNO3 (0.68g) was dissolved in a glass beaker filed with of 40ml double distilled water DDW. This solution added to second beaker containing solution of 0.6M thiourea CS(NH2)2 (1.82g) (source of sulfur) dissolved in in an alkaline solution of NH3 and the pH of the solution has been adjusted to be 8 in all experiments. The temperature of solution was
Results and discussion
Fig. 2 shows the film thickness with error bars as a function of deposition time, the thickness of the film increases linearly with deposition time. The deposition rate was estimated and found to be 0.58nm/min.
Fig. 3 shows the XRD patterns of Ag2S films deposited on the silicon substrate at different deposition times. The XRD peaks were noticed at 2θ = 20.04°, 25.2°, 28.24°, 32.9°, 35°, 36.4°, 37.3, 39.8°, 42.7°, and 52.9° corresponding to (-101) (-111), (111), (112),(120), (121), (-103),
Conclusions
The effect of the deposition time on the structural, electrical and optical properties of Ag2S film prepared by chemical bath deposition technique was investigated. XRD revealed that the grown films were polycrystalline with monoclinic structure. The intensity of XRD peaks increased with film thickness. The film morphology was found to be strongly depended on the deposition time. Mixed nanoparticles and nanotubes morphologies were observed for Ag2S film deposited at 10hr. The direct optical
Declaration of Competing Interest
None.
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