Faculty Publications
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Item Effect of substrate temperature on the suitability of thermally deposited cadmium sulfide thin films as window layer in photovoltaic cells(Academic Press, 2018) Barman, B.; Bangera, K.V.; Shivakumar, G.K.Cadmium sulfide has been studied as an important material in solar energy research because of its energy band gap and attractive electrical characteristics. While thin films of cadmium sulfide have been found to be useful as window layer in a solar cell, the role of various deposition parameters is yet to be understood. In the current study, the role of substrate temperature on the characteristics of the CdS thin films is analyzed. Thin films of cadmium sulfide (?450 nm thick) were deposited at various substrate temperatures viz., 300 K, 323 K, 373 K, and 423 K onto clean glass substrates by vacuum thermal evaporation method. The structural, morphological, and opto-electrical properties of the deposited films were studied as a function of substrate temperature. X-ray diffraction (XRD) study revealed that the thin films are polycrystalline in nature and having a hexagonal wurtzite crystal structure along (002) plane. Scanning electron microscopy (SEM) along with energy dispersive spectroscopy (EDS) revealed that the grown films are homogeneous, uniform and pin-hole free. All the films deposited at various substrate temperature displayed high optical transmittance (>60%) in the visible range. The optical energy band gap of the films was estimated using Tauc's plot and was found to increase by a slight margin with an increase in the substrate temperature and decrease at higher substrate temperature. The photosensitivity was found to be highest for the CdS thin film grown at a substrate temperature of 373 K. © 2018 Elsevier LtdItem A comprehensive study on the structural, morphological, compositional and optical properties of ZnxCd1-xS thin films(Institute of Physics Publishing helen.craven@iop.org, 2019) Barman, B.; Bangera, K.V.; Shivakumar, G.K.The absorption loss in cadmium sulfide (CdS) thin films which are widely used as a window layer in a photovoltaic cell limits the efficiency of the device. This issue can be addressed by ZnxCd1-xS thin films due to its tunable band gap nature. Herein, the various composition of ZnxCd1-xS (x=0, 0.15, 0.30, 0.45, 0.70, 0.85, 1) thin films were grown by a vacuum thermal evaporation technique and the characteristics of the films were investigated by varying the composition 'x'. The x-ray diffraction (XRD) studies displayed that the as-deposited films consist of diffraction peaks from both CdS and ZnS lattice. The formation of ternary ZnxCd1-xS films was verified when the deposited films were subjected to an annealing treatment. The morphology of the films was analyzed using a scanning electron microscope (SEM) and it was observed that the films are uniform, homogeneous and free from any pin-holes and cracks. The presence of Zn, Cd and S elements were quantized using an energy dispersive spectroscopy. Optical studies showed a successful non-linear band gap engineering (2.42-3.49 eV) for the deposited ZnxCd1-xS thin films. All films showed a very high optical transmittance of above 70% in the visible wavelength region. © 2020 IOP Publishing Ltd.Item Preparation of thermally deposited Cux(ZnS)1-x thin films for opto-electronic devices(Elsevier Ltd, 2019) Barman, B.; Bangera, K.V.; Shivakumar, G.K.Zinc sulfide thin films have been doped with copper atoms to investigate their efficiency as transparent conductor layers. Cux(ZnS)1-x thin films were deposited on glass substrate using thermal evaporation technique by varying the Cu concentration (x = 0.01, 0.02, 0.03, 0.05, 0.10 and 0.25). The prepared thin films were characterized using XRD, FE-SEM, EDS and UV–Vis spectroscopy. The X-ray diffraction studies revealed that the films are crystalline in nature and well oriented along (111) direction with the cubic crystal structure. Crystallite size increases with increase in Cu concentration. FE-SEM studies showed that the films are homogenous and pin-hole free. All the films exhibited p-type conductivity. It was also observed that the band gap of the Cux(ZnS)1-x films vary from 3.48 eV to 2.60 eV when the copper content varies from 0 to 0.25. At a Cu concentration of x = 0.03, the hole conductivity increases to 1.9 × 103 S/m retaining an optical transparency of ?73% in the visible spectra. This combination of optical transparency and hole conductivity of Cux(ZnS)1-x thin films for such low Cu concentration is, to our knowledge, the best reported to date. © 2018Item ZnxCd1-xS thin films: A study towards its application as a reliable photodetector(Academic Press, 2020) Barman, B.; Bangera, K.V.; Shivakumar, G.K.A reliable and stable photodetector shows enormous potential applications in health monitoring, intelligent wearable devices, and biological sensing. The noble opto-electrical properties of cadmium sulfide (CdS) makes it a favorable semiconductor for opto-electrical devices. The properties of CdS thin film can further be enhanced by alloying it with zinc sulfide (ZnS) to form ZnxCd1-xS compound semiconductor. Herein, a high performance, ZnxCd1-xS (x = 0, 0.15, 0.30, and 0.45) photodetector with good stability is designed and fabricated via a simple vacuum thermal evaporation technique. The various photodetector parameters of the ZnxCd1-xS films were investigated as a function of its composition. Among the various compositions of the ZnxCd1-xS thin films, the Zn0.15Cd0.85S films displayed excellent photosensitivity as high as 2.22 which is ~1.6 times higher than that of undoped CdS thin films. The research data suggests that a high-performance single layer ZnxCd1-xS photodetector with good stability and reproducibility can be fabricated using a thermal evaporation technique. © 2019 Elsevier LtdItem ZnxSn1-xS thin films: A study on its tunable opto-electrical properties for application towards a high efficient photodetector(Elsevier Ltd, 2020) Barman, B.; Bangera, K.V.; Shivakumar, G.K.Zinc sulfide (ZnS) and tin sulfide (SnS) are crucial semiconductors with potential use in various opto-electronic applications. By incorporating ZnS and SnS to form ZnxSn1-xS thin film, one can expect exceptional opto-electrical properties due to their large band gap dissimilarity. Herein, thin films of ZnxSn1-xS (0.0 ? x ? 1.0) were successfully deposited on glass substrates using a thermal evaporation method for the first time and its various properties were analyzed. X-ray diffraction (XRD) analysis confirmed the polycrystalline behavior of ZnxSn1-xS films with a preferred orientation along the (1 1 1) plane. The absence of any secondary peaks along with the shift in the (1 1 1) peak position to lower 2? values with increasing Zn concentration confirmed the formation of a solid solution. SEM analysis depicted the presence of uniform and homogeneous films. The formation of nearly stoichiometric ZnxSn1-xS films was verified using an energy dispersive spectroscopy (EDS). The electrical and optical properties of the films were estimated from the two-probe method and UV–Vis spectroscopy, respectively. The energy band gap values decreased from 3.49 eV to 1.54 eV as the composition of the ZnxSn1-xS films was varied. The various opto-electrical parameters were investigated and the photosensitivity was found highest at 43.38 for the Zn0.10Sn0.90S films. The observed tunable opto-electrical properties of the ZnxSn1-xS films suggests that the films can be utilized for a wide range of opto-electronic applications. © 2020 International Solar Energy SocietyItem ZnSxSe1−x thin films: A study into its tunable energy band gap property using an experimental and theoretical approach(Elsevier Ltd, 2022) Ray, S.; Barman, B.; Darshan, C.; Tarafder, K.; Bangera, K.V.In recent times, ZnS and ZnSe thin films are drawing tremendous attention towards opto-electrical devices due to their optimal wide band gap energy. By alloying ZnS and ZnSe films to obtain ZnSxSe1−x thin films, the band gap of the ZnSxSe1−x film can be tuned to a value according to the device requirements. Herein, ZnSxSe1−x thin films were deposited on pre-cleaned glass substrates using a thermal evaporation system and the various properties of the obtained thin films were analyzed by altering the percentage of sulfur concentration in the films. The XRD analysis illustrated that the prepared films are polycrystalline in nature and oriented along cubic (1 1 1) plane. The deviation of (1 1 1) preferential peak position with composition ‘x’ along the absence of any secondary peaks confirms the formation of ternary ZnSxSe1−x thin films. DFT analysis verifies the formation of pristine ZnSxSe1−x alloy system. FESEM micrographs displayed that the ZnSxSe1−x thin films do not have any cracks or pinholes. EDAX analysis of the films revealed the existence of Zn, Se and S in an appropriate quantity. Optical analysis revealed the effective band gap tailoring of ZnSxSe1−x thin films. The band gap of the ZnSxSe1−x thin films increases from 2.59 eV to 3.38 eV as the composition ‘x’ varied from 0 to 1 and band composition was determined using the DOS plot obtained using VASP. © 2022 International Solar Energy Society