Faculty Publications
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Item Photoconductivity has been studied in cadmium selenide thin films prepared by thermal evaporation in vacuum. Attempts have been made to correlate the photoresponse with the deposition conditions. It has been observed that as-grown films, irrespective of the cadmium content, are not photosensitive and that baking in air, especially above 723 K, leads to considerable improvement in the photoconducting properties of cadmium selenide films.(Photoconductivity in vacuum deposited cadmium selenide thin films) Rajendra, B.V.; Kasturi, V.B.; Shivakumar, G.K.2004Item The effect of substrate temperature on the structural, optical and electrical properties of vacuum deposited ZnTe thin films(2009) Rao, G.K.; Bangera, K.V.; Shivakumar, G.K.The present paper reports the effect of substrate temperature on the structural, optical and electrical properties of vacuum deposited zinc telluride (ZnTe) thin films. X-ray diffraction (XRD) analysis of the films, deposited on glass substrates, revealed that they have cubic structure with strong (111) texture. Room temperature deposits are tellurium rich and an increase in the substrate temperature up to 553 °K results in stoichiometric films. Electrical conductivity has been observed to increase with the increase in substrate temperature, accompanied by increase in the carrier concentration and the mobility of the carriers. The optical bandgap energy and the thermal activation energy of the films have also been evaluated. © 2009 Elsevier Ltd. All rights reserved.Item Studies on the photoconductivity of vacuum deposited ZnTe thin films(2010) Rao, K.G.; Bangera, K.V.; Shivakumar, G.K.The present paper reports the analysis of photoconductivity of vacuum deposited zinc telluride (ZnTe) thin films as a function of substrate temperature and post-deposition annealing. Detailed analyses were first carried out to understand the effect of substrate temperature and annealing on the structure, composition, optical and electrical properties of the films. The films deposited at elevated substrate temperatures showed faster and improved photoresponse. Post-deposition annealing was found to further enhance the photoresponse of the films. Attempts have been made to explain the improvement in the photoresponse on the basis of structural and compositional changes, taking place in the films, due to the substrate temperature and annealing. © 2010 Elsevier Ltd. All rights reserved.Item Properties of ZnO:Bi thin films prepared by spray pyrolysis technique(Elsevier Ltd, 2013) Sadananda Kumar, N.; Bangera, K.V.; Anandan, C.; Shivakumar, G.K.Undoped and Bi doped zinc oxide thin films were deposited on glass substrate at 450 °C using spray pyrolysis technique. The X-ray diffraction studies shows that Bi doped ZnO films are polycrystalline hexagonal structure with a preferred orientation along (101) direction. Crystallites size of the films decreases with increasing doping concentration. Scanning electron microscope image shows change in the surface morphology. The composition of Zn, O and Bi elements in the undoped and Bi doped ZnO films were investigated by X-ray photoelectron spectroscopy. Bi doped ZnO thin films show a transparency nearly 75% in the visible region. The optical band gap of ZnO thin films reduces from 3.25 eV to 3.12 eV with an increase in Bi concentration from 0 to 5at.% respectively. Electrical conductivity of ZnO thin films increased from 0.156 to 6.02S/cm with increasing Bi dopant concentration from 0% to 5% respectively. © 2013 Elsevier B.V. All rights reserved.Item Influence of substrate temperature and post deposition annealing on the properties of vacuum deposited ZnSe thin films(2013) Rao, K.; Bangera, K.V.; Shivakumar, G.K.The effects of substrate temperature and post deposition annealing on the structural, optical and electrical properties of vacuum deposited ZnSe thin films are presented here. The chemical composition of the films varied drastically with substrate temperature which in turn caused changes in various properties of the films. The grain size of the films increased with substrate temperature and also after annealing. The electrical properties of the films were found to be varying as a function of chemical composition and grain size. © 2012 Elsevier Ltd.Item 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.Item 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).Item Properties of CdxZn1-xO thin films and their enhanced gas sensing performance(Elsevier Ltd, 2017) Bharath, S.P.; Bangera, K.V.; Shivakumar, G.K.CdxZn1-xO(0 ? x ? 0.20) thin films with different Cd concentrations were successfully deposited on glass substrate using spray pyrolysis technique. X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDAX) were used for structural, surface morphological and compositional characterization. The XRD analysis revealed that the synthesized films were hexagonal in structure with (002) orientation. The SEM studies confirm the formation of homogeneous and uniform films. Optical transmittance and electrical conductivity of the films were evaluated using UV–Visible spectroscopy and two probe method respectively. The optical studies showed that the CdxZn1-xO thin films have optical transmittance in entire visible region. The resistivity of undoped films were very high and it decreases with addition of cadmium. The gas sensing properties were investigated at optimal temperature of 350 °C for various volatile organic compounds like acetone, ethanol and methanol. The CdxZn1-xO thin films with 10 at. % cadmium concentration showed the sensitivity of 50% for 1 ppm ethanol. © 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 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.