Journal Articles
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Item Characterization of p-CdTe/n-CdS hetero-junctions(2009) Mahesha, M.G.; Bangera, K.V.; Shivakumar, G.K.Nano-crystalline CdTe/CdS thin film hetero-junctions have been grown on glass substrate by thermal evaporation technique. The growth conditions to get stoichiometric compound films have been optimized. The grown hetero-junctions have been characterized for their I-V characteristics. Analysis of I-V characteristics has been made to investigate the current conduction mechanism in p-CdTe/n-CdS hetero-junction. The band gap energy of cadmium telluride and cadmium sulfide films have been computed from the study of variation of resistance with temperature. Based on the study, band diagram for p-CdTe/n-CdS hetero-junction has been proposed.Item Fabrication and characterization of thermal evaporated n-Si/ p-ZnTe thin film heterojunction diodes(2013) Rao, K.; Bangera, K.V.; Shivakumar, G.K.The paper reports the fabrication and detailed electrical characterization of thermal evaporated n-Si/p-ZnTe thin film heterojunction diodes. The heterojunction diodes were prepared by depositing ZnTe films on n-Si substrates. The conduction mechanism, barrier height, space charge density and width of the depletion region were determined by I-V and C-V characteristics of the heterojunction diodes. The bandgap and activation energies of n-Si and p-ZnTe were also determined and a theoretical band diagram of n-Si/p-ZnTe heterojunction was drawn based on Anderson's model. © 2012 Elsevier B.V. All rights reserved.Item Study of the doping of thermally evaporated zinc oxide thin films with indium and indium oxide(Springer Nature, 2013) Palimar, S.; Bangera, K.V.; Shivakumar, G.K.The present paper reports observations made on investigations carried out to study structural, optical and electrical properties of thermally evaporated ZnO thin films and their modulations on doping with metallic indium and indium oxide separately. ZnO thin film in the undoped state is found to have a very good conductivity of 90 ?–1 cm–1 with an excellent transmittance of up to 90 % in the visible region. After doping with metallic indium, the conductivity of the film is found to be 580 ?–1 cm–1, whereas the conductivity of indium oxide-doped films is increased up to 3.5 × 103 ?–1 cm–1. Further, the optical band gap of the ZnO thin film is widened from 3.26 to 3.3 eV when doped with indium oxide and with metallic indium it decreases to 3.2 eV. There is no considerable change in the transmittance of the films after doping. All undoped and doped films were amorphous in nature with smooth and flat surface without significant modifications due to doping. © 2012, The Author(s).Item Electrical characterization of vacuum-deposited p-CdTe/n-ZnSe heterojunctions(Springer Nature, 2015) Acharya, S.; Bangera, K.V.; Shivakumar, G.K.In this paper, we report a heterojunction of p-CdTe/n-ZnSe fabricated on a quartz substrate using thermal evaporation technique. The materials have a larger band gap difference in comparison to other II–VI heterojunctions-involving CdTe. The larger band gap difference is expected to increase diffusion potential and photovoltaic conversion efficiency. The electrical conduction mechanism involved, barrier height and band offset at the interface that are crucial to determine device performance are evaluated using electrical characterization of heterojunction. The junction exhibited excellent rectification behavior with an estimated barrier height of 0.9 eV. © 2015, The Author(s).Item Band gap engineering of mixed Cd(1?x)Zn(x)Se thin films(Elsevier Ltd, 2017) Santhosh, T.C.M.; Bangera, K.V.; Shivakumar, G.K.This paper deals with band gap engineering in CdZnSe thin films. This was achieved by adding different amounts of zinc selenide (ZnSe) to cadmium selenide (CdSe). The weight percentage of ZnSe (x) was varied from 0 to 1 in steps of 0.2. The films were prepared using thermal evaporation technique. The structural analysis was carried out using X-ray diffraction. Surface morphology and elemental composition of the grown films was investigated using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) respectively. As deposited cadmium selenide thin films were dark reddish in color, changes to lemon-yellow with increase in ZnSe concentration. Electrical transport studies have been carried out using two probe method. Resistivity of the mixed films increased with increase in ZnSe concentration and it shows semiconducting behavior. It is observed that activation energy for conduction increases from 0.39 eV to 0.85 eV with increase in ZnSe concentration. Optical properties of the films were analyzed from absorption and transmittance studies. It is observed that the optical band gap increases gradually from 1.67 eV to 2.60 eV as ‘x’ varied from 0 to 1. © 2017 Elsevier B.V.Item Synthesis and band gap tuning in CdSe(1-x)Te(x) thin films for solar cell applications(Elsevier Ltd, 2017) Santhosh, T.C.M.; Bangera, K.V.; Shivakumar, G.K.Thin films of CdSe(1-x)Te(x) (x = 0 – 1) were grown on to the glass substrates by thermal evaporation method (PVD). The effect of annealing duration on the formation of single phase ternary alloys were systematically investigated. The prepared thin films were characterized by using FE-SEM, EDS and X-ray diffractometer. The X-ray diffraction studies shows that vacuum annealed films are polycrystalline in nature, and well oriented along a preferred direction of (0 0 2) for hexagonal and along (1 1 1) for cubic crystal structure. It is observed that increase in the CdTe concentration leads to change in the crystal structure from hexagonal to cubic. The absorption coefficients and optical band gaps were evaluated from spectrometric measurements. It is observed that optical band gap can be tuned from 1.67 eV to 1.51 eV as value of x varied from 0 to 1. © 2017 Elsevier LtdItem Structural, electrical and optical properties of stoichiometric In2Te3 thin films(Elsevier Ltd, 2017) Vallem, V.; Bangera, K.V.; Shivakumar, G.K.In2Te3 thin films were grown by thermal evaporation technique. The annealing of films played a major role to obtain stoichiometry, regardless of substrate temperature. Annealing at 300 ?C resulted in well oriented, mono-phased and nearly stoichiometric In2Te3 thin films. The variation in grain size of In2Te3 films associated with the substrate temperatures provides a significant control over the resistivity of the films, and the resistivity decreased with an increase in the grain size. The activation energy and optical band gap of stoichiometric In2Te3 films were found to be 0.01±0.005 eV and 0.99±0.02 eV, respectively. The absorption co-efficient of these films was found to be of the order of 105 cm?1. © 2016 Elsevier Ltd and Techna Group S.r.l.Item Effect of Bi doping on the properties of CdSe thin films for optoelectronic device applications(Elsevier Ltd, 2017) Santhosh, T.C.M.; Bangera, K.V.; G.k, S.CdSe and Bi (1%, 2%, 3%) doped CdSe thin films were deposited on the glass substrates using thermal evaporation technique. Effect of Bi doping on the structural, optical, electrical and photo response properties of CdSe thin films were investigated. The X-ray diffraction studies reveals that undoped and Bi doped CdSe films are polycrystalline in nature with hexagonal crystal structure along (002) direction. No significant changes are observed in the lattice parameters or the grain size indicating minimum lattice distortion. The optical band gap of undoped CdSe film was estimated to be 1.67 eV. Replacement of cadmium by bismuth results in an increase in the electrical conductivity of doped films. Doping with bismuth is found to improve the photo sensitivity of CdSe thin films. © 2017 Elsevier LtdItem 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.