Faculty Publications
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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 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 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 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.Item Study on structural, optical and electrical properties of spray pyrolysed PbxZn1-xS thin films for opto-Electronic applications(Elsevier GmbH journals@elsevier.com, 2017) Veena, E.; Bangera, K.V.; Shivakumar, G.K.Ternary thin films are attractive for many applications due to their band gap tunability. In the present study, the stoichiometric n-PbxZn1-xS (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1) thin films were deposited on glass substrates using spray pyrolysis technique. The structural, optical and electrical studies have been carried out in order to understand the band gap tunability of prepared films. The XRD analysis confirmed that the prepared films were polycrystalline in nature with cubic structure. The substitution of zinc into the lead sulphide lattice led to decrease in the crystallite size, and the orientation of the films changed from (200) to (111) plane. SEM images clearly showed a modification in the morphology of the films from nano size particle to network structure due to Zn ion substitution. The optical band gap energy of PbxZn1-xS thin films varied from 0.40 eV to 3.54 eV and the transition has been changed from indirect to direct with the substitution of zinc into the lead lattice site. The resistivity and activation energy of the films were increased with increase in the band gap. The results confirm the formation of a continues solid solution of PbS and ZnS in the ternary phase which can be a suitable candidate for optoelectronic applications. © 2017 Elsevier GmbHItem Enhanced thermoelectric power of Al and Sb doped In 2 Te 3 thin films(Elsevier Ltd, 2019) Vallem, V.; Bangera, K.V.; G.k, S.Aluminium and antimony are used as dopants for In 2 Te 3 to study their influence on the thermoelectric power of the films. Both aluminium and antimony are expected to replace indium in the film and contribute to the structural, electrical and thermoelectric behaviour of indium telluride. It is observed that addition of both Al and Sb dopants induced an additional phase of free Te. The electrical conductivity of In 2 Te 3 films is observed to reduce with Al doping and increase with Sb doping when compared with the electrical conductivity of un-doped films. The thermoelectric power is found to be maximum for 2.1% Al doped and 1% Sb doped films. Moreover, the thermoelectric power factor of In 2 Te 3 films is found to be enhanced 3.1 times for 2.1% doping of Al and 8.7 times for 1% Sb doping. © 2019 Elsevier LtdItem Synthesis of single-phase stoichiometric InTe thin films for opto-electronic applications(Academic Press, 2019) Vallem, V.; Bangera, K.V.; G.k, S.Mono-phased and stoichiometric InTe thin films were successfully prepared using vacuum evaporation technique. A systematic variation in substrate temperature and annealing temperature along with annealing duration resulted stoichiometric and single phase InTe films. The annealing treatment of as-deposited films resulted in the structural transformation from mixed phase of In 2 Te 3 and InTe to mono-phased InTe. The electrical conductivity of stoichiometric single phase films was found to be 15.612 ? ?1 cm ?1 . The optical band gap of stoichiometric InTe films was found to be 1.42 eV and absorption coefficient of the films was of the order of 10 6 cm ?1 . Electrical properties of mono-phased films accompanied with optical properties such as direct band gap and absorption coefficient makes them suitable for optoelectronic devices. © 2019 Elsevier Ltd