Browsing by Author "Bangera, K.V."

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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.
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.
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.
Conduction Mechanism in n-CdSe/p-ZnTe Heterojunction
(Springer New York LLC barbara.b.bertram@gsk.com, 2016) Acharya, S.; Bangera, K.V.; Shivakumar, G.K.
This work reports on fabrication using vacuum evaporation and characterization of n-CdSe/p-ZnTe heterojunctions. Before forming the junction, CdSe and ZnTe layers were characterized for crystal structure and chemical composition to account for observed electrical properties. The heterojunction was characterized by current–voltage (I–V) measurements, temperature dependence of reverse saturation current, admittance, and capacitance–voltage (C–V) measurements. I–V characteristics of the heterojunction exhibited clear diode nature with rectification ratio of 9.05 at ±0.5 V and ideality factor n = 3.34. From the temperature dependence of the I–V characteristic, a barrier height ?b of 0.36 eV was determined for the CdSe–ZnTe junction. Conduction mechanism analysis revealed contributions from both thermionic and space-charge-limited conduction. Furthermore, the shunt leakage current was found to be space-charge limited, showing symmetry in current near V = 0 V. The dependence of capacitance on frequency and bias voltage has been analyzed to identify the bulk and interface defects. These measurements indicate the presence of bulk defects and high series resistance, severely affecting current transport. © 2016, The Minerals, Metals & Materials Society.
Conduction mechanisms in vacuum deposited p-ZnTe/n-Si heterojunction diodes
(2011) Rao, K.G.; Bangera, K.V.; Shivakumar, G.K.
p-ZnTe/n-Si heterojunction diodes were prepared by vacuum depositing ZnTe films on n-Si substrates. Detailed electrical characterization was performed to determine the conduction mechanisms operating in the diode. Important parameters such as ideality factor and barrier height were also determined. � 2011 American Institute of Physics.
Conduction mechanisms in vacuum deposited p-ZnTe/n-Si heterojunction diodes
(2011) Rao, G.K.; Bangera, K.V.; Shivakumar, G.K.
p-ZnTe/n-Si heterojunction diodes were prepared by vacuum depositing ZnTe films on n-Si substrates. Detailed electrical characterization was performed to determine the conduction mechanisms operating in the diode. Important parameters such as ideality factor and barrier height were also determined. Â© 2011 American Institute of Physics.
Conductive and transparent undoped ZnO thin films prepared by thermal evaporation method
(2012) Palimar, S.; Shivakumar, G.K.; Bangera, K.V.
Zinc Oxide thin films were obtained by thermal evaporation method. The films were then subjected to detailed structural, optical and electrical studies. The analysis has showed that the obtained films have a transmittance of up to 95% in the visible region of the electromagnetic spectrum with a room temperature conductivity of around 92 ?-1cm-1. A detailed analysis of the result is reported. � 2012 American Institute of Physics.
Conductive and transparent undoped ZnO thin films prepared by thermal evaporation method
(2012) Palimar, S.; Shivakumar, G.K.; Bangera, K.V.
Zinc Oxide thin films were obtained by thermal evaporation method. The films were then subjected to detailed structural, optical and electrical studies. The analysis has showed that the obtained films have a transmittance of up to 95% in the visible region of the electromagnetic spectrum with a room temperature conductivity of around 92 Î©-1cm-1. A detailed analysis of the result is reported. Â© 2012 American Institute of Physics.
Drastic increase in thermoelectric power factor of mixed Sb2Te3-In2Te3 thin films
(Academic Press, 2019) Vallem, S.; Bangera, K.V.; G.k, S.
Thermoelectric power factor is an indicator of the performance of a thermoelectric material. Attempts have been made by various techniques, like doping, to improve the thermoelectric conversion efficiency of materials. In the present study, a layer structured thermoelectric material Sb2Te3 is alloyed to In2Te3 using vacuum deposition method at 423 K to significantly enhance the power factor of ?118 ?Wm-1K?2 (at 450 K). Structurally, all films were polycrystalline in nature as clearly reflected in XRD patterns. All films were showing p-type conductivity, and electrical conductivity of In2Te3 films increased with increasing Sb2Te3 content. The seebeck coefficient is found to be higher for un-doped In2Te3 than that of Sb2Te3-In2Te3 and pure Sb2Te3 films. However, the thermoelectric power factor of 25% Sb2Te3 alloyed In2Te3 films is enhanced by 11.9 times that of In2Te3 films and 4 times that of Sb2Te3 films at 320 K. It is interesting to note that efficiency of the mixed films is higher than that of the individual films. © 2019 Elsevier Ltd
Effect of Ag in CdSe thin films prepared using thermal evaporation
(Maik Nauka-Interperiodica Publishing, 2017) Santhosh, T.C.M.; Bangera, K.V.; Shivakumar, G.K.
It has been a general practice to dope thin films with suitable dopants to modify the properties of the films to make them more suitable for potential applications. When the dopant concentrations are low, they do not normally affect the structure and morphology of the films. However, it may lead to drastic changes in electronic properties of the films. This might result from the dopant getting incorporated into the lattice of the material of the films. Cadmium selenide is an important compound semiconductor material with an attractive energy band gap. The present work relates to an attempt made to dope CdSe thin films with silver. CdSe:Ag (1–5%) thin films were deposited on glass substrates at an optimized substrate temperature of 453 K using thermal evaporation technique. The grown films were analyzed using X-ray diffraction, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDX) techniques. It is observed that undoped CdSe thin films and CdSe:Ag films have hexagonal structure. The grain size was found to increase marginally with an increase in the Ag concentration. The optical band gap of the films determined by optical transmission measurements agree with that of CdSe. Electrical conductivity is observed to increase from 10–4 to 3.66 (? cm)–1 on addition of silver. The variation of resistance with temperature indicates that the prepared films consist of CdSe and Ag existing as two separate phases coexisting and contributing individually to the resistivity of the films. © 2017, Pleiades Publishing, Ltd.
Effect of annealing on the properties of Bi doped ZnO thin films grown by spray pyrolysis technique
(Academic Press, 2014) Sadananda Kumar, N.; Bangera, K.V.; Shivakumar, G.K.
The effect of annealing temperature on the structural, optical and electrical properties of transparent and conducting Bi doped ZnO (BZO) films deposited on glass substrate by spray pyrolysis technique was investigated. The BZO thin films were annealed in the temperature range from 450 °C to 550°C for 4 h in air atmosphere. The grain size of the BZO films increased with increasing annealing temperature. The annealed BZO films were electrically stable and there was a drastic change in the electrical conductivity after annealing. The films annealed at 500°C showed better conductivity and optical transmittance. © 2014 Elsevier Ltd. All rights reserved.
Effect of annealing on the properties of Sb doped ZnO thin films prepared by spray pyrolysis technique
(2014) Kumar, N.S.; Bangera, K.V.; Shivakumar, G.K.
Sb doped ZnO thin films have been deposited on glass substrate at 450�C using spray pyrolysis technique. The X-ray diffraction studies revealed that the as deposited films are polycrystalline in nature with (100) preferred orientation. Whereas the films annealed at 450� C for 6h show a preferential orientation along (101) direction. Crystallites size varies from 15.7 nm to 34.95 nm with annealing duration. The Scanning electron microscopic analysis shows the plane and smooth surface of the films. The optical properties of annealed films have shown a variation in the band gap between 3.37 eV and 3.19 eV. Transparency of as grown and annealed films decreases from 78 % to 65% respectively in the visible region. The electrical conductivity of the as grown film shows an increase in the electrical conductivity by one order of magnitude with increase in the annealing duration. � 2014 AIP Publishing LLC.
Effect of annealing on the properties of Sb doped ZnO thin films prepared by spray pyrolysis technique
(American Institute of Physics Inc. subs@aip.org, 2014) Kumar, N.S.; Bangera, K.V.; Shivakumar, G.K.
Sb doped ZnO thin films have been deposited on glass substrate at 450Â°C using spray pyrolysis technique. The X-ray diffraction studies revealed that the as deposited films are polycrystalline in nature with (100) preferred orientation. Whereas the films annealed at 450Â° C for 6h show a preferential orientation along (101) direction. Crystallites size varies from 15.7 nm to 34.95 nm with annealing duration. The Scanning electron microscopic analysis shows the plane and smooth surface of the films. The optical properties of annealed films have shown a variation in the band gap between 3.37 eV and 3.19 eV. Transparency of as grown and annealed films decreases from 78 % to 65% respectively in the visible region. The electrical conductivity of the as grown film shows an increase in the electrical conductivity by one order of magnitude with increase in the annealing duration. Â© 2014 AIP Publishing LLC.
Effect of annealing on the properties of spray-pyrolysed lead sulphide thin films for solar cell application
(Springer Verlag service@springer.de, 2017) Veena, E.; Bangera, K.V.; Shivakumar, G.K.
Annealing is the most important processing parameter perhaps as it directly affects the properties of the thin films. In the present article, lead sulphide thin films composed of (2 0 0) plane-oriented nano-rods were successfully synthesized on glass substrates using spray pyrolysis technique at annealing temperature 350 °C. Films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive analysis by X-ray (EDAX), UV–VIS–NIR spectrometry and two-probe experiments. The X-ray diffraction study confirmed that films exhibiting face-centred cubic structure with a preferred orientation along (2 0 0) plane were independent of annealing temperature. SEM photographs revealed the formation of nano-rods. The possible formation of nano-rods and its dependency on optical and electrical properties were discussed. Chemical composition in terms of atomic ratio of the constituents is determined from EDAX studies. The optical band gap of the lead sulphide thin films was found to decrease from 1.22 to 0.98 eV with an increase in annealing temperature. The electrical conductivity of the films at room temperature was of the order of 10?2 ??1 cm?1 with the low activation energy. Results prove that lead sulphide films grown by chemical method appeal its adoptability for potential solar cell applications. © 2017, Springer-Verlag Berlin Heidelberg.
Effect of annealing on the properties of zinc oxide nanofiber thin films grown by spray pyrolysis technique
(Springer Nature, 2014) Sadananda Kumar, N.; Bangera, K.V.; Shivakumar, G.K.
Zinc oxide nanofiber thin films have been deposited on glass substrate by spray pyrolysis technique. The X-ray diffraction studies revealed that the films are polycrystalline with the hexagonal structure and a preferred orientation along (002) direction for films annealed for 1 h at 450 °C. Further increase in annealing time changes the preferred orientation to (100) direction. The scanning electron microscopic analysis showed the formation of ZnO nanofiber with an average diameter of approximately 800 nm for annealed films. The compositional analysis of nanofiber ZnO thin films were studied by time of flight secondary ion mass spectroscopy, which indicated oxygen deficiency in the films. The optical properties of annealed films have shown a variation in the band gap between 3.29 and 3.20 eV. The electrical conductivity of the as grown and annealed films showed an increase in the conductivity by two orders of magnitude with increase in annealing duration. © 2013, The Author(s).
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 Ltd
Effect of cadmium incorporation on the properties of zinc oxide thin films
(Springer Nature, 2018) Bharath, S.P.; Bangera, K.V.; Shivakumar, G.K.
CdxZn1-xO (0 ? x ? 0.20) thin films are deposited on soda lime glass substrates using spray pyrolysis technique. To check the thermal stability, CdxZn1-xO thin films are subjected to annealing. Both the as-deposited and annealed CdxZn1-xO thin films are characterized using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy-dispersive X-ray analysis (EDAX) to check the structural, surface morphological and compositional properties, respectively. XRD analysis reveals that the both as-deposited and annealed CdxZn1-xO thin films are (002) oriented with wurtzite structure. SEM studies confirm that as-deposited, as well as annealed CdxZn1-xO thin films are free from pinholes and cracks. Compositional analysis shows the deficiency in Cd content after annealing. Optical properties evaluated from UV-Vis spectroscopy shows red shift in the band gap for CdxZn1-xO thin films. Electrical property measured using two probe method shows a decrease in the resistance after Cd incorporation. The results indicate that cadmium can be successfully incorporated in zinc oxide thin films to achieve structural changes in the properties of films. © Springer-Verlag GmbH Germany, part of Springer Nature 2018.
Effect of indium content on the characteristics of indium tin oxide thin films
(Institute of Physics Publishing helen.craven@iop.org, 2018) Navya, K.; Bharath, S.P.; Bangera, K.V.; Shivakumar, G.K.
Transparent IxT1-xO (x = 0 to 1) alloyed thin films were deposited by spray pyrolysis technique at a substrate temperature of 400 °C. The effect of incorporation of indium on structural, optical and electrical properties of tin oxide thin films were studied. Characterization of thin films was carried out using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDAX), UV-Visible absorption spectroscopy. XRD results revealed that IxT1-xO thin films were polycrystalline in nature with good crystallinity. Incorporation of indium effectively modifies the surface morphology of the films. The band gap was varied from 3.7 eV to 3 eV. Maximum electrical conductivity of 44.52 × 103 ?-1 m-1 and transmittance of 90% is obtained for I0.5T0.5O films, hence can be used as highly transparent and conducting electrodes. © 2018 IOP Publishing Ltd.
Effect of substrate temperature and film thickness on the thermoelectric properties of In2Te3 thin films
(Elsevier Ltd, 2017) Vallem, V.; Bangera, K.V.; Shivakumar, G.K.
Herein, the thermoelectric properties of vacuum deposited In2Te3 thin films were investigated by varying the substrate temperature and the thickness of the films. The thermo-electro motive force of the prepared films was found to increase with an increase in the substrate temperature up to 423 K and then decrease at 473 K due to the presence of mixed-phase structure. The maximum thermoelectric power of 220 ?V/K was observed for the films deposited at 423 K substrate temperature, which was found to decrease with increase in thickness. The films deposited at 423 K with 150 nm thickness showed maximum power factor of 27 ?Wm?1K?2 at 450 K. These observations are explained on the basis of structural, morphological and compositional changes. © 2017 Elsevier B.V.
Effect of substrate temperature on the structural and electrical properties of spray deposited lead sulfide thin films
(2016) Veena, E.; Bangera, K.V.; Shivakumar, G.K.
Lead sulfide (PbS) thin films were prepared by chemical spray pyrolysis method using lead acetate and thiourea as precursors of Pb+2 and S-2 ions. X-ray diffraction (XRD) technique, scanning electron microscope (SEM) and EDAX analysis were used for structural, morphological and compositional characterization. XRD analysis shows that the films are cubic in nature with a preferred orientation along (2 0 0). EDAX analysis shows that films deposited at 150�C are sulfur rich. An increase in the substrate temperature results in a decrease in the sulfur content of the prepared film. It has been observed that thin films deposited at or above 225�C are smooth & uniform morphologically. Beyond a substrate temperature of 275�C, the films become discontinuous and non-uniform. However, the films are sulfur rich, even at 275�C. Electrical conductivity of prepared thin films have been measured using silver contacts in coplanar geometry. Films are n - type as confirmed by hot probe technique. The electrical conductivity at room temperature (25�C) was in the order of 10-4 ?-1cm-1 and was found to increase with increase in temperature showing the semiconducting nature of the films with the band gap of 0.39 eV. � 2016 Elsevier Ltd.