Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
5 results
Search Results
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 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 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 substrate temperature on the suitability of thermally deposited cadmium sulfide thin films as window layer in photovoltaic cells(Academic Press, 2018) Barman, B.; Bangera, K.V.; Shivakumar, G.K.Cadmium sulfide has been studied as an important material in solar energy research because of its energy band gap and attractive electrical characteristics. While thin films of cadmium sulfide have been found to be useful as window layer in a solar cell, the role of various deposition parameters is yet to be understood. In the current study, the role of substrate temperature on the characteristics of the CdS thin films is analyzed. Thin films of cadmium sulfide (?450 nm thick) were deposited at various substrate temperatures viz., 300 K, 323 K, 373 K, and 423 K onto clean glass substrates by vacuum thermal evaporation method. The structural, morphological, and opto-electrical properties of the deposited films were studied as a function of substrate temperature. X-ray diffraction (XRD) study revealed that the thin films are polycrystalline in nature and having a hexagonal wurtzite crystal structure along (002) plane. Scanning electron microscopy (SEM) along with energy dispersive spectroscopy (EDS) revealed that the grown films are homogeneous, uniform and pin-hole free. All the films deposited at various substrate temperature displayed high optical transmittance (>60%) in the visible range. The optical energy band gap of the films was estimated using Tauc's plot and was found to increase by a slight margin with an increase in the substrate temperature and decrease at higher substrate temperature. The photosensitivity was found to be highest for the CdS thin film grown at a substrate temperature of 373 K. © 2018 Elsevier LtdItem Preparation of thermally deposited Cux(ZnS)1-x thin films for opto-electronic devices(Elsevier Ltd, 2019) Barman, B.; Bangera, K.V.; Shivakumar, G.K.Zinc sulfide thin films have been doped with copper atoms to investigate their efficiency as transparent conductor layers. Cux(ZnS)1-x thin films were deposited on glass substrate using thermal evaporation technique by varying the Cu concentration (x = 0.01, 0.02, 0.03, 0.05, 0.10 and 0.25). The prepared thin films were characterized using XRD, FE-SEM, EDS and UV–Vis spectroscopy. The X-ray diffraction studies revealed that the films are crystalline in nature and well oriented along (111) direction with the cubic crystal structure. Crystallite size increases with increase in Cu concentration. FE-SEM studies showed that the films are homogenous and pin-hole free. All the films exhibited p-type conductivity. It was also observed that the band gap of the Cux(ZnS)1-x films vary from 3.48 eV to 2.60 eV when the copper content varies from 0 to 0.25. At a Cu concentration of x = 0.03, the hole conductivity increases to 1.9 × 103 S/m retaining an optical transparency of ?73% in the visible spectra. This combination of optical transparency and hole conductivity of Cux(ZnS)1-x thin films for such low Cu concentration is, to our knowledge, the best reported to date. © 2018