Faculty Publications
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Item 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 The p-type doping of vacuum deposited ZnTe thin films with bismuth by a new technique of using nano-spheres(Elsevier Ltd, 2010) Rao, K.G.; Shivakumar, G.K.; Kasturi, V.B.The present paper reports the successful doping of vacuum evaporated zinc telluride (ZnTe) thin films with bismuth by a new technique of using nano-spheres. The discontinuous films of bismuth (the dopant material), containing bismuth in the form of nano-spheres, were prepared by vacuum evaporation and the ZnTe films were then deposited on top of them. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were used to ascertain the formation of discontinuous bismuth films and the proper diffusion of bismuth in ZnTe films, respectively. After doping, the carrier concentration of the ZnTe films was found to increase by an order of the magnitude. The electrical conductivity also improved significantly. The photoconductivity and photo-response properties of the doped films were also analysed. © 2010 Elsevier B.V. All rights reserved.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 Effect of substrate temperature on the characteristics of ZnO films produced by a combination of thermal vapor deposition and oxidation processes(Springer New York LLC barbara.b.bertram@gsk.com, 2017) Sneha, C.; Prabukumar, C.; Jayalakshmi, M.; Bhat, S.; Bhat, K.In the present work, ZnO semiconductor films were prepared by following two step processes, namely, thermal vapor deposition of the zinc on the glass substrate followed by oxidative annealing. Substrate temperature during deposition of the zinc was varied. Structural properties and morphology of the ZnO films were investigated by using X-ray diffraction and scanning electron microscopy techniques. Hydrophobic nature of the film was confirmed by using contact angle analyser. Hall measurements facilitated the estimation of the carrier concentration, their mobility and their effect on the conductivity. Photoluminescence spectroscopy was used to analyse the lattice defect concentration in the film. Further, the sensor response of the ZnO film to CO gas was analysed. Sensor fabricated with ZnO films which were prepared by oxidizing Zn films deposited at higher substrate temperature were found to possess better response and faster response-recovery time than the film prepared using lower substrate temperature for zinc deposition. © 2017, Springer Science+Business Media, LLC.Item A balancing between super transparency and conductivity of solution combustion derived titanium doped indium oxide: Effect of charge carrier density and mobility(Elsevier B.V., 2018) Pujar, P.; Vardhan, R.V.; Gupta, D.; Mandal, S.In this contribution, super transparent (~100%) and conducting In14Ti1O23 (Titanium doped Indium oxide; InTiO) films were reported via solution combustion processing with acetylacetone as fuel. Both bulk-powder and thin film systems were studied and revealed the efficacy of low temperature combustion synthesis which yielded crystalline InTiO powder at 150 °C and its film counterpart had shown pronounced crystalinity with temperature. Also, all films with varying annealing temperature were smooth with rms value ranging from 0.29 nm to 1.9 nm. In addition, the charge carrier density in all films found to be of the order 1019 cm?3, possessing highest transparency nearly equals to uncoated glass at an annealing temperature of 350 °C having maximum of ~67% metal-oxygen-metal framework (or lattice oxygen) confirmed via X-ray photoelectron spectroscopy. Also, the highest conductivity of 20 S/cm at an annealing temperature of 450 °C clearly conveyed the potential of solution combustion processing in the fabrication of ultra-transparent InTiO films with no sophistication in the film fabrication. © 2018Item Resonance levels in GeTe thermoelectrics: Zinc as a new multifaceted dopant(Royal Society of Chemistry, 2020) Bhat, D.K.; Shenoy, U.S.Recently doping has been widely used in enhancing the thermoelectric properties of lead-free GeTe. But much of the work has been concentrated on carrier concentration tuning or phonon scattering. Until now, only indium has been reported to be the best resonant dopant in cubic GeTe. Herein, for the first time we introduce zinc as a resonant dopant to the cubic GeTe family. We show that zinc in GeTe not only introduces resonance states but also increases the band gap and raises the heavy hole valence band above the light hole valence band leading to enhanced Seebeck values. This multifunctional dopant incorporation in GeTe leads to enhanced transport properties as predicted by Boltzmann transport properties calculations based on first principles density functional theory electronic structure calculations. This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.Item Complementary effect of co-doping aliovalent elements Bi and Sb in self-compensated SnTe-based thermoelectric materials(Royal Society of Chemistry, 2021) Kihoi, S.K.; Shenoy, U.S.; Bhat, D.K.; Lee, H.S.Research on Pb-free thermoelectric materials as a potential eco-friendly and solid-state source of energy has continuously advanced over time, with SnTe-based materials having shown utmost promising properties owing to their tunable electronic structure and scalable thermal conductivity. In this study, we self-compensate Sn to reduce inherent Sn vacancies, and further tune the carrier concentration by doping with Bi. Sb is further alloyed to incorporate nanostructures that significantly reduce the thermal conductivity. Multiple aliovalent dopants result in a continually decreased carrier concentration and subsequent significantly decreased electrical conductivity. The Seebeck values are seen to increase with temperature, where a maximum value of ?171 ?V K?1is reported with a maximum power factor of ?22.7 ?W cm?1K?2. We show through first principles DFT calculations the synergistic effect of Bi and Sb to introduce resonance states and an additional valence band convergence effect with increasing Sb that contribute to improved electronic properties. A decreased phonon frequency with co-doping is also reported. A maximumZTof ?0.8 at 823 K is reported in the Sn0.90Bi0.03Sb0.10Te composition, showing good potential in Sb co-doped SnTe-based materials. © The Royal Society of Chemistry 2021.Item Boronic Acid-Based n-Type Semiconductor for Electronic Device Application(Springer, 2022) Kagatikar, S.; Dhanya, D.; Kekuda, D.; Satyanarayana, M.N.; Kulkarni, S.D.; Karkera, C.Electron transporting, or n-type, semiconductors can serve as charge-transport materials, and are ideal for use in organic electronic devices. Boron-based small organic molecules have garnered immense research attention as the heteroatom can effectively alter the electronic structures leading to excellent photophysical and electrochemical properties. A luminescent Schiff base (E)-(4-((2-(2-hydroxybenzoyl)hydrazono)methyl)phenyl)boronic acid (SHB) was prepared by a one-pot condensation reaction between salicyloyl hydrazide and formylphenylboronic acid. The synthesized molecule was chemically characterized by infrared spectroscopy, nuclear magnetic resonance spectroscopy, and mass spectrometry. The blue-emitting boronic acid-derived molecule displayed intramolecular charge transfer, high carrier concentration, good thermal stability, a reversible reduction tendency and formation of uniform amorphous thin films. A diode was successfully fabricated via a solution processing technique with an ideality factor of 7.76. Further, AC conductivity, dielectric constant, dielectric loss, and capacitance values in a frequency range of 10–1000 Hz were extracted from dielectric studies. The dielectric constant of SHB was found to be 9.71 with an AC conductivity of 6.34 × 10−9 Ω−1 cm−1 at 1000 Hz. Graphical Abstract: [Figure not available: see fulltext.] © 2022, The Author(s).Item Probing of Bi doped GeTe thermoelectrics leads to revelation of resonant states(Elsevier Ltd, 2022) Shenoy, U.S.; D, G.K.; Bhat, D.K.Quest for lead free high performance mid temperature thermoelectric materials has led to extensive research on SnTe and GeTe based materials. Among various strategies implemented to improve the transport properties of GeTe, electronic structure engineering holds a prominent place. Herein, we reinvestigate the impact of substitutional doping of Bi in GeTe on its electronic structure in both rhombohedral and cubic phase. We uncover that Bi introduces resonance levels in GeTe acting as a first n-type resonant dopant in both rhombohedral and cubic phases. We also report for the first time that Bi resonance states undergo Rashba splitting in low temperature rhombohedral phase. Bi doping acts in a multifunctional way by tuning the carrier concentration, causing conduction band convergence and phonon scattering in addition to improving the band effective mass by distorting the density of states near the Fermi level to enhance the thermoelectric performance of the material. The convergence of L, Z and Σ valence bands in rhombohedral phase due to Bi doping leads to manifestation of Rashba effect in p-type material which was not reported till date. Thus, we propose that the chemical potential tuning can result in p-type as well as n-type Bi doped GeTe for thermoelectric application. © 2022 Elsevier B.V.Item High-Performance All-Optical Hybrid Plasmonic Switch Using Zn-Doped Cadmium Oxide(Institute of Electrical and Electronics Engineers Inc., 2023) Sahu, S.K.; Singh, M.In this article, a novel hybrid plasmonic waveguide (HPWG)-based all-optical switch (AOS) using zinc-doped cadmium oxide (ZnCdO) is reported and numerically investigated with the finite-element method. This oxide layer, which is a well-known transparent conductive oxide (TCO), can be switched from a dielectric to a metallic phase by electrical tuning the refractive index. The mobility of free-carrier concentration is highly magnified with a nonlinear optical effect induced by the epsilon-near-zero material near the telecommunication wavelength. We have simulated the plasmonic switch using the COMSOL Multiphysics simulator, predicting 13.75 dB extinction ratio (ER), 0.5 dB insertion loss (IL), and 27.5 figure-of-merit (FoM) at 1.55 \mu \text{m} wavelength. We also performed the reliability study by varying parameters, such as the width and height of the waveguide, which affect the performance of the on-chip switch design. In addition, the proposed AOS can be easily integrated with future silicon photonic circuits for ultrafast switching applications. © 1973-2012 IEEE.