Faculty Publications
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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 Third-order nonlinear optical properties of Mn doped ZnO thin films under cw laser illumination(Elsevier B.V., 2013) Nagaraja, K.K.; Pramodini, S.; Santhosh Kumar, A.; Nagaraja, H.S.; Poornesh, P.; Kekuda, D.We report the measurements of third-order nonlinear optical properties of undoped zinc oxide and manganese doped zinc oxide thin films with different doping concentrations investigated using z-scan technique. Thin films were prepared by radio frequency magnetron sputtering using a compound target on glass substrate at room temperature. The structural properties of the deposited films were analysed by X-ray diffraction studies. The atomic force microscope analysis of the deposited films reveals that the grain size and roughness of the films depend on the Mn concentration. The direct energy band gap of the deposited film increases with the increase in Mn concentration in the films. The nonlinear optical measurements were carried out using a cw He-Ne laser at 633 nm wavelength. The z-scan results reveal that the films exhibit self-defocusing nonlinearity. The third-order nonlinear optical susceptibility ?(3) is found to be of the order of 10-3 esu. The films investigated here exhibit good optical power limiting at the experimental wavelength. © 2012 Elsevier B.V. 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 Effect of Sn doping on structural, optical, electrical and wettability properties of oriented ZnO nanorod arrays(2013) Santhosh Kumar, A.; Nagaraja, K.K.; Nagaraja, H.S.Herein we present a modified sol gel route for the one step fabrication of oriented ZnO nanorod arrays. The method is seed layer free, and nanorods directly attach to a substrate. We also present the effect of tin (Sn) content on the crystallinity, microstructural, optical and electrical properties of the ZnO nanorod arrays. Thermo gravimetric (TG) curves of gel precursors showed that most of the organic groups and other volatiles were removed at about 450 C. X-ray diffraction patterns confirmed that the films were polycrystalline in nature with (002) preferred orientation. The texture coefficient, grain size, dislocation density and lattice parameters of the ZnO arrays were determined. The SEM micrographs revealed that the undoped and 1 at.%Sn doped films were composed of nanorods and the concentration of 2 at.%Sn doping hindered the rod like structure growth and modulated into granular nature. UV-visible transmission spectroscopy indicated that the transparency of the films increased with Sn content. On Sn doping, the films also exhibited a red shift and slight shrinkage of band gap. The electrical studies revealed that 1 at.% of Sn doping enhanced electrical conduction in ZnO films and beyond that the distortion caused in the lattice reduced the conductivity. The contact angle of the ZnO nanostructures varied between 91 and 115 depending upon the Sn content. Therefore, 1 at.%Sn doping into ZnO nanorods improves the crystallinity, electrical conductivity and water contact angle. © 2013 Springer Science+Business Media New York.Item Study of the doping of thermally evaporated zinc oxide thin films with indium and indium oxide(Springer Nature, 2013) Palimar, S.; Bangera, K.V.; Shivakumar, G.K.The present paper reports observations made on investigations carried out to study structural, optical and electrical properties of thermally evaporated ZnO thin films and their modulations on doping with metallic indium and indium oxide separately. ZnO thin film in the undoped state is found to have a very good conductivity of 90 ?–1 cm–1 with an excellent transmittance of up to 90 % in the visible region. After doping with metallic indium, the conductivity of the film is found to be 580 ?–1 cm–1, whereas the conductivity of indium oxide-doped films is increased up to 3.5 × 103 ?–1 cm–1. Further, the optical band gap of the ZnO thin film is widened from 3.26 to 3.3 eV when doped with indium oxide and with metallic indium it decreases to 3.2 eV. There is no considerable change in the transmittance of the films after doping. All undoped and doped films were amorphous in nature with smooth and flat surface without significant modifications due to doping. © 2012, The Author(s).Item Influence of Sn doping on photoluminescence and photoelectrochemical properties of ZnO nanorod arrays(Kluwer Academic Publishers, 2014) Santhosh Kumar, A.S.; Huang, N.M.; Nagaraja, H.S.Herein, the nanostructured Sn containing ZnO is directly synthesized on the surface of substrate by modified sol gel approach under low-temperature condition. The samples are characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), Raman-scattering, photoluminescence (PL) and photoelectrochemical analyses. The SEM micrographs show that the undoped and 1 at. % Sn doped films are composed of nanorods and the concentration of 2 at. % Sn doping hinders the rod-like structure's growth and modulates into granular nature. The investigations of XRD reveal that the synthesized undoped and Sn doped ZnO nanorods possess a perfect hexagonal growth habit of wurtzite zinc oxide, along the (002) direction of preference. The Raman spectra demonstrate that the vibrational mode of E1(LO), which is very weak in undoped and 1at. % Sn doped ZnO, is strongly enhanced with 2 at. % Sn doping into ZnO lattice. PL spectra show that strong UV emission in pure and 1 at. % Sn doped ZnO, while there is dominant green emission in 2 at. % Sn doped ZnO. Moreover, all the samples are photo electrochemically active and exhibit the highest photocurrent of 28 ?A for the 1 at. % Sn doped ZnO nanorod arrays in 0.2M Na2SO4 electrolyte, on light irradiation. Time dependent photoresponse tests are carried out by measuring the photocurrent under chopped light irradiation. © 2014 The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht.Item Structural, linear, and nonlinear optical properties of radio frequency-sputtered nitrogen-doped ZnO thin films studied using z-scan technique(Institute of Physics Publishing custserv@iop.org, 2014) Nagaraja, K.K.; Pramodini, S.; Santhosh Kumar, A.S.; Nagaraja, H.S.; Poornesh, P.The third-order nonlinear optical properties of undoped and nitrogen-doped ZnO thin films were evaluated using the z-scan technique. The films were sputter-deposited on glass substrates using radio frequency power. The He-Ne continuous wave laser operating at 633 nm was used as an irradiation source. A change in the growth mode in the nitrogen-doped films was observed. The grain size and roughness were found to be dependent on the nitrogen concentration, as shown by atomic force microscopy analysis. The optical band gap was determined and found to increase with nitrogen concentration in the films. Both nonlinear absorption and refraction nonlinearities were exhibited by the deposited films. The nonlinear refractive index n2, the nonlinear absorption coefficient ?eff and the third-order nonlinear optical susceptibility ?(3) were determined and found to be largest. Multiple diffraction ring patterns were observed when the samples were made to interact with the laser beam and were attributed to refractive index change and thermal lensing. Further, optical power-limiting experiments were performed to determine the optical-limiting threshold and clamping values for undoped and nitrogen-doped ZnO films. © 2014 Astro 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 Preparation, characterization and photoelectrochemical properties of hydrophilic Sn doped TiO2 nanostructures(Elsevier, 2014) Santhosh Kumar, A.S.; Nagaraja, K.K.; Huang, N.M.; Nagaraja, H.S.Abstract Hydrophilic Sn doped TiO2 nanostructured thin films have been fabricated using a sol-gel method, and followed by calcination at 450 C. The samples are characterized by means of XRD, Raman, SEM and contact angle measurements. The XRD and Raman studies revealed that, the higher Sn doping content (3 at%) leads to the formation of mixed phases of TiO2. SEM micrographs revealed that all samples are porous in nature. The contact angle of TiO2 nanostructured films varied between 19 and 37 depending upon the Sn content. All the samples are photoelectrochemically active and 2% Sn doping significantly enhances the photoelectrochemical ability of TiO 2 film. The highest photocurrent density of 20 ?A cm-2 is measured for 2 at% Sn doped TiO2 in 0.2 M Na2SO 4 electrolyte, on light irradiation. Time dependent photoresponse tests have been carried out by measuring the photocurrent under chopped light irradiation. © 2014 Elsevier B.V.Item Influence of annealing on the linear and nonlinear optical properties of Mn doped ZnO thin films examined by z-scan technique in CW regime(Elsevier B.V., 2016) Nagaraja, K.K.; Pramodini, S.; Poornesh, P.; Rao, A.; Nagaraja, H.S.We present the studies on the influence of annealing on the third-order nonlinear optical properties of RF magnetron sputtered manganese doped zinc oxide (MZO) thin films with different doping concentration. It is revealed that the incorporation of Mn into ZnO and annealing lead to prominent changes in the third order nonlinearity. Nonlinear optical measurements were carried out by employing the z-scan technique using a continuous wave (CW) He-Ne laser of 633 nm. The z-scan results reveal that the films exhibit self-defocusing thermal nonlinearity. The third-order nonlinear optical susceptibility ?(3) was found to be of the order of 10-3 esu and 10-2 esu for annealed MZO thin films at 200 °C and 400 °C respectively. The dependence of grain size on the observed nonlinearity was revealed by atomic force microscopy analysis. Optical limiting studies were carried out for a range of input power levels and an optical limiting of about ?8 mW was observed indicating the possible application for photonic devices. © 2016 Elsevier B.V. All rights reserved.