Faculty Publications
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Item Characterization of ZnO films produced by thermal evaporation and oxidation(Trans Tech Publications Ltd ttp@transtec.ch, 2015) Prabukumar, C.; Jayalakshmi, M.; Bhat, K.ZnO nanostructures such as nanowires and nanorods are beneficial in solar energy harvesting because they provide a structure with a large surface area. Also, they provide a direct pathway to electron transportation, eliminating the scope for grain boundary scattering. In this investigation, thin ZnO films were prepared by thermal evaporation of the Zn metal, which was followed by oxidation. Evaporation parameters and oxidation temperatures were fixed. The oxidation duration was the variable. The effect of oxidation time, on the morphology and structural properties were studied by using scanning electron microscopy and X-ray diffractometry. The study shows that with increase in oxidation time, the morphology changed to nanorods from initial flake morphology. As a function of oxidation time, the crystallinity and texture became more dominant. By using, I-V characteristic curves, it was found that the morphology changes alter the surface electrical conductivity of the prepared ZnO films. © (2015) Trans Tech Publications, Switzerland.Item Preparation of vacuum deposited cadmium selenide thin films for optoelectronic applications(Elsevier Ltd, 2016) Santhosh, T.C.M.; Bangera, K.V.; Shivakumar, G.K.Cadmium selenide is a direct band gap material which finds applications in optoelectronic devices. Preparation of the compound semiconductor in thin film form with stable electrical characterization has been investigated in the present study. As deposited films at room temperature (25°C) are non-stoichiometric with excess cadmium and films grown at 180°C substrate temperature are stoichiometric and homogeneous. The crystallinity increases with increase in substrate temperature. The optical band gap determined from absorption measurements lie in the range 1.89 eV - 2.02 eV. Electrical conductivity measurements made in a temperature range from 25°C to 200°C yield thermal activation energy of 0.52eV for stoichiometric films. Films deposited at 180° C and annealed at 200° C for two hours are found to be stabilized in its electrical and structural properties. © 2016 Elsevier Ltd.Item Synthesis and characterization of Cu doped CdTe thin films for solar cell application(Elsevier Ltd, 2019) Ray, S.; Bangera, K.V.; Tarafder, K.Synthesis and characterization of thin-film based photovoltaic materials attract with great research interest for the past few years as the efficiency of the photovoltaic cell can be improved systematically with a proper functionalization of the films and making multilayers. We have synthesized Cu-doped CdTe thin films with different doping concentrations using the PVD technique. The structural, morphological, and optical properties of synthesized films were carefully investigated. Our study shows that all the prepared films are polycrystalline with a cubic structure. The morphological studies (SEM) reveal that all the films are crack and pinhole-free. The composition and stoichiometry of the film were confirmed by energy dispersive spectroscopy (EDS) study. The optical characterization of the samples is performed by using UV- VIS-NIR spectrometer. The result shows interesting optical behavior of the film suitable for solar cell applications. © 2019 Elsevier Ltd. All rights reserved.Item Characterization of thin film Al/p-CdTe schottky diode(2008) Mahesha, M.G.; Kasturi, V.B.; Shivakumar, G.K.A study has been made on the behavior of Al/p-CdTe thin film junction grown by thermal evaporation method. I-V characteristics show that the Al makes Schottky contact with p-CdTe. The variation of junction capacitance with frequency and voltage has been studied to evaluate the barrier height. The activation energy and band gap have been estimated by studying variation of resistivity with temperature. Using all these data, band diagram of Al/p-CdTe has been proposed. © TÜB?TAK.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 Study of the aluminium oxide doped zinc oxide thin films prepared by thermal evaporation technique(2012) Palimar, S.; Banger, K.V.; Shivakumar, G.K.The present study reports the observations made on investigations carried out to study structural, optical and electrical properties of aluminium oxide doped ZnO thin films obtained by thermal evaporation technique. Films obtained are found to be amorphous in nature with smooth and continuous surface. Room temperature conductivity of the film is found to be 5x10 3 U -1 cm -1 with visible region transmittance of above 95%. The optical energy gap of the film is found to be 3.25 eV. From the calculations of activation energy, it is observed that the doped ZnO film has two donor levels, one at 142 meV and other at 43 meV. A detailed analysis of the result is reported. © 2012 Asian Network for Scientific Information.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.
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