Faculty Publications
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Item Semiconducting thin films of cadmium telluride, both p-type and n-type, have been prepared by conventional thermal evaporation technique. The influence of various growth parameters such as the rate of deposition, deposition temperature, post-deposition heat treatment, and source material composition has been investigated. The films deposited at high deposition rates and low substrate temperatures exhibited an excess of tellurium and showed a p-type conductivity, whereas those deposited at high substrate temperature and low deposition rates contained excess cadmium and are n-type in nature. An intrinsic bandgap of 1.49 eV for stoichiometric films obtained by both electrical and optical characterization is reported.(Growth and characterization of vacuum deposited cadmium telluride thin films) Shreekanthan, K.N.; Kasturi, V.B.; Shivakumar, G.K.2003Item 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 Studies on vacuum deposited p-ZnTe/n-CdTe heterojunction diodes(2011) Rao, K.G.; Bangera, K.V.; Shivakumar, G.K.The present paper reports the fabrication and detailed electrical characterization of p-ZnTe/n-CdTe heterojunction diodes prepared by vacuum deposition method. The possible conduction mechanisms of the heterojunction diode were determined by analyzing the I-V characteristics. The C-V characteristics of the heterojunction diodes were studied to determine the barrier height, carrier concentration and thickness of the depletion region in the heterojunction. A theoretical band diagram of the heterojunction was drawn based on Anderson's model. © 2010 Elsevier Ltd. All rights reserved.Item Role of cadmium on corrosion resistance of Zn-Ni alloy coatings(Allerton Press Inc. journals@allertonpress.com, 2014) Rao, V.R.; Hegde, A.C.Cadmium (Cd) catalyzed Zn-Ni alloy plating has been accomplished galvanostatically on mild steel (MS) using gelatin and glycerol as additives. The effect of addition of Cd into Zn-Ni bath has been examined in terms of nickel (Ni) content and corrosion resistance of Zn-Ni-Cd ternary alloy coatings. The process and product of electrolysis under different concentrations of additives and Cd have been investigated by cyclic voltammetry (CV). The effects of current density (c.d.) on Ni content of the alloy have been studied by spectrophotometric method, supported by EDX analysis. The deposition has been carried out under different concentrations of Cd ranging from 0.004 to 0.1 M. The corrosion rates (CR) of Zn-Ni alloy coatings have been found to decrease drastically with addition of Cd. It has been also revealed that the CR of binary Zn-Ni alloy coatings decreased with the increase of Cd concentration only up to a certain optimal concentration, i.e., up to 0.02 M, and then remained unchanged. An effort to change the anomalous type of codeposition into normal one by changing the molar ratios of the metal ions, i.e. [Cd2+]/[Ni2+] as 0.01, 0.05 and 0.25 has remained futile. CV study demonstrated an important role of Cd in mutual depositions of Zn2+ and Ni2+ ions by its preferential adsorption, thus leading to the increased Ni content of the alloy. The bath composition and operating parameters have been optimized for deposition of bright and uniform Zn-Ni-Cd alloy coatings. Changes in the surface morphology and phase structure of Zn-Ni alloy coatings due to addition of Cd has been confirmed by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) study respectively. Experimental investigations so as to identify the role of Cd in codeposition Zn-Ni alloy coatings have been carried out and the results are discussed. © 2014 Allerton Press, Inc.Item Electrofabrication of multilayer Fe-Ni alloy coatings for better corrosion protection(Springer Verlag service@springer.de, 2014) Ullal, Y.; Hegde, A.C.Electrofabrication of multilayer Fe-Ni alloy coatings were accomplished successfully on mild steel and their corrosion behaviors were studied. Multilayer comprised of alternatively formed 'nano-size' layers of Fe-Ni alloy of different composition have been produced from a single bath having Fe 2+and Ni2+ ions using modulated (i.e. periodic pulse control) current density (cd). The deposition conditions were optimized for both composition and thickness of individual layers for best performance of the coatings against corrosion. The deposits were analyzed using scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), Hardness Tester, electrochemical AC and DC methods respectively. The multi layered deposits showed better corrosion resistances compared to the monolayer Fe-Ni (CR = 3.77 mm year-1) coating deposited using DC from the same bath; the maximum corrosion resistance being shown by the coating having 300 layers, deposited at cyclic cathodic current densities of 2.0 and 4.0 A dm-2 (CR = 0.03 mm year-1). Drastic improvement in the corrosion performance of multilayer coatings were explained in the light of changed kinetics of mass transfer at cathode and increased surface area due to modulation and layering. © 2014 Springer-Verlag Berlin Heidelberg.Item Magnetically induced codeposition of Ni-Cd alloy coatings for better corrosion protection(American Chemical Society service@acs.org, 2014) Rao, V.R.; Hegde, A.C.The effects of applied magnetic field, B (both parallel and perpendicular) during process of electrodeposition of Ni-Cd alloy coating on mild steel from a newly proposed electrolytic bath have been studied by using X-ray diffraction (XRD), energy-dispersive X-ray (EDX), and scanning electron microscopy (SEM) analysis. Both parallel and perpendicular B reduced the corrosion rates (CRs); however, the effect is more pronounced in case of perpendicular B. Progressive decrease of CR with increase in the intensity of B showed that corrosion protection efficacy bears close relation with changed composition and crystallographic orientation of the coatings. Under optimal condition, Ni-Cd coating deposited at 0.8 T (perpendicular) was found to be 35 times less corrosive than the conventional Ni-Cd coating (B = 0 T) deposited from the same bath for same time. The effect of B on thickness, microhardness, surface morphology, composition, and crystallographic orientation, and hence, the corrosion resistance of the coatings were analyzed in the light of magnetohydrodynamic (MHD) effect. © 2014 American Chemical Society.Item ZnxCd1-xS thin films: A study towards its application as a reliable photodetector(Academic Press, 2020) Barman, B.; Bangera, K.V.; Shivakumar, G.K.A reliable and stable photodetector shows enormous potential applications in health monitoring, intelligent wearable devices, and biological sensing. The noble opto-electrical properties of cadmium sulfide (CdS) makes it a favorable semiconductor for opto-electrical devices. The properties of CdS thin film can further be enhanced by alloying it with zinc sulfide (ZnS) to form ZnxCd1-xS compound semiconductor. Herein, a high performance, ZnxCd1-xS (x = 0, 0.15, 0.30, and 0.45) photodetector with good stability is designed and fabricated via a simple vacuum thermal evaporation technique. The various photodetector parameters of the ZnxCd1-xS films were investigated as a function of its composition. Among the various compositions of the ZnxCd1-xS thin films, the Zn0.15Cd0.85S films displayed excellent photosensitivity as high as 2.22 which is ~1.6 times higher than that of undoped CdS thin films. The research data suggests that a high-performance single layer ZnxCd1-xS photodetector with good stability and reproducibility can be fabricated using a thermal evaporation technique. © 2019 Elsevier LtdItem Synergistic manifestation of band and scattering engineering in the single aliovalent Sb alloyed anharmonic SnTe alloy in concurrence with rule of parsimony(Royal Society of Chemistry, 2021) Basu, R.; Mandava, S.; Shenoy, U.S.; Bhat, D.K.; Khasimsaheb, B.; Debnath, A.K.; Singh, A.; Neeleshwar, S.Several endeavors were adapted to improve the thermoelectric performance of SnTe as a substitute of toxic PbTe and the booming approaches comprise introduction of nanostructuring, resonance states, valence band convergence and interstitial or substitutional defects. In this study, a stratagem was designed to incorporate single aliovalent Sb in SnTe by a one-step approach which successfully modulates the electronic and thermal transport properties by integration of several approaches, viz. energy-filtering effect, valence band convergence and phonon scattering at all length scales synergistically. Here, the alteration of the band structure of SnTe incorporated with Sb leads to substantial improvement of the Seebeck coefficient, essentially beneficial for the performance of thermoelectric alloys, beyond the designated critical temperature at 473 K which shows the onset of strong contribution of the heavy (?) valence band. The experimental finding of band convergence by Sb was for the first time corroborated by theoretical validation by Density Functional Theory (DFT) calculations. In addition, the presence of mass fluctuation, secondary precipitates, interfaces and the long-range interactions due to resonant bonding leading to optical phonon softening, large phase space available for three-phonon scattering and strong anharmonicity enables an ultralow lattice thermal conductivity of ?0.5 W m-1 K-1. Thus, a zT value of ?0.72 at 775 K is recorded for the SnTeSb0.05 composition, which is 154% enhancement compared to our pristine SnTe and is strongly competing with numerous reported zT values using considerably less abundant Ag, Ge, In and highly toxic Pb, Hg, Bi, Cd multiple elements as either a dopant or an additive. Thus, the law of parsimony is maintained with reduction in the cost of the thermoelectric module. © The Royal Society of Chemistry.