Faculty Publications
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Item Preparation of vacuum deposited cadmium selenide thin films for optoelectronic applications(Elsevier Ltd, 2016) Santhosh, T.C.M.; Bangera, K.V.; Shivakumar, G.K.Cadmium selenide is a direct band gap material which finds applications in optoelectronic devices. Preparation of the compound semiconductor in thin film form with stable electrical characterization has been investigated in the present study. As deposited films at room temperature (25°C) are non-stoichiometric with excess cadmium and films grown at 180°C substrate temperature are stoichiometric and homogeneous. The crystallinity increases with increase in substrate temperature. The optical band gap determined from absorption measurements lie in the range 1.89 eV - 2.02 eV. Electrical conductivity measurements made in a temperature range from 25°C to 200°C yield thermal activation energy of 0.52eV for stoichiometric films. Films deposited at 180° C and annealed at 200° C for two hours are found to be stabilized in its electrical and structural properties. © 2016 Elsevier Ltd.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 Studies on vacuum deposited p-ZnTe/n-ZnSe heterojunction diodes(2010) Rao, K.G.; Bangera, K.V.; Shivakumar, G.K.p-ZnTe/n-ZnSe heterojunction diodes were prepared by vacuum deposition and a detailed electrical characterization of the heterojunction was performed. The I-V and C-V characteristics of the heterojunction diodes were studied to determine the conduction mechanism, barrier height, space charge density and thickness of the depletion region in the heterojunction. The bandgap and activation energies of n-ZnSe and p-ZnTe were also determined and a theoretical band diagram of p-ZnTe/n-ZnSe heterojunction was drawn based on Anderson's model. © 2010 Elsevier Ltd. All rights reserved.Item Fabrication and characterization of thermal evaporated n-Si/ p-ZnTe thin film heterojunction diodes(2013) Rao, K.; Bangera, K.V.; Shivakumar, G.K.The paper reports the fabrication and detailed electrical characterization of thermal evaporated n-Si/p-ZnTe thin film heterojunction diodes. The heterojunction diodes were prepared by depositing ZnTe films on n-Si substrates. The conduction mechanism, barrier height, space charge density and width of the depletion region were determined by I-V and C-V characteristics of the heterojunction diodes. The bandgap and activation energies of n-Si and p-ZnTe were also determined and a theoretical band diagram of n-Si/p-ZnTe heterojunction was drawn based on Anderson's model. © 2012 Elsevier B.V. All rights reserved.Item Band gap engineering of mixed Cd(1?x)Zn(x)Se thin films(Elsevier Ltd, 2017) Santhosh, T.C.M.; Bangera, K.V.; Shivakumar, G.K.This paper deals with band gap engineering in CdZnSe thin films. This was achieved by adding different amounts of zinc selenide (ZnSe) to cadmium selenide (CdSe). The weight percentage of ZnSe (x) was varied from 0 to 1 in steps of 0.2. The films were prepared using thermal evaporation technique. The structural analysis was carried out using X-ray diffraction. Surface morphology and elemental composition of the grown films was investigated using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) respectively. As deposited cadmium selenide thin films were dark reddish in color, changes to lemon-yellow with increase in ZnSe concentration. Electrical transport studies have been carried out using two probe method. Resistivity of the mixed films increased with increase in ZnSe concentration and it shows semiconducting behavior. It is observed that activation energy for conduction increases from 0.39 eV to 0.85 eV with increase in ZnSe concentration. Optical properties of the films were analyzed from absorption and transmittance studies. It is observed that the optical band gap increases gradually from 1.67 eV to 2.60 eV as ‘x’ varied from 0 to 1. © 2017 Elsevier B.V.Item Structural, electrical and optical properties of stoichiometric In2Te3 thin films(Elsevier Ltd, 2017) Vallem, V.; Bangera, K.V.; Shivakumar, G.K.In2Te3 thin films were grown by thermal evaporation technique. The annealing of films played a major role to obtain stoichiometry, regardless of substrate temperature. Annealing at 300 ?C resulted in well oriented, mono-phased and nearly stoichiometric In2Te3 thin films. The variation in grain size of In2Te3 films associated with the substrate temperatures provides a significant control over the resistivity of the films, and the resistivity decreased with an increase in the grain size. The activation energy and optical band gap of stoichiometric In2Te3 films were found to be 0.01±0.005 eV and 0.99±0.02 eV, respectively. The absorption co-efficient of these films was found to be of the order of 105 cm?1. © 2016 Elsevier Ltd and Techna Group S.r.l.Item Effect of annealing on the properties of spray-pyrolysed lead sulphide thin films for solar cell application(Springer Verlag service@springer.de, 2017) Veena, E.; Bangera, K.V.; Shivakumar, G.K.Annealing is the most important processing parameter perhaps as it directly affects the properties of the thin films. In the present article, lead sulphide thin films composed of (2 0 0) plane-oriented nano-rods were successfully synthesized on glass substrates using spray pyrolysis technique at annealing temperature 350 °C. Films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive analysis by X-ray (EDAX), UV–VIS–NIR spectrometry and two-probe experiments. The X-ray diffraction study confirmed that films exhibiting face-centred cubic structure with a preferred orientation along (2 0 0) plane were independent of annealing temperature. SEM photographs revealed the formation of nano-rods. The possible formation of nano-rods and its dependency on optical and electrical properties were discussed. Chemical composition in terms of atomic ratio of the constituents is determined from EDAX studies. The optical band gap of the lead sulphide thin films was found to decrease from 1.22 to 0.98 eV with an increase in annealing temperature. The electrical conductivity of the films at room temperature was of the order of 10?2 ??1 cm?1 with the low activation energy. Results prove that lead sulphide films grown by chemical method appeal its adoptability for potential solar cell applications. © 2017, Springer-Verlag Berlin Heidelberg.Item Effective role of thickness on structural, electrical and optical properties of lead sulphide thin films for photovoltaic applications(Elsevier Ltd, 2017) Veena, E.; Bangera, K.V.; Shivakumar, G.K.The n-type lead sulphide thin films were deposited at 350 °C substrate temperature on glass substrates using advanced spray pyrolysis technique. The thickness of the thin films played an important role to improve the properties of lead sulphide and to use in device fabrication apart from various deposition parameters. The films deposited at thickness of 520 nm resulted in a well oriented polycrystalline with face-centered cubic structure. An enhancement in the crystallite size with increase in film thickness was evidenced by XRD and SEM. The variation in crystallite size of films associated with different thickness provides a significant control over optical and electrical properties. The resistivity of the thin films decreased with an increase in thickness was of the order of 102 ? cm. The activation energy and optical band gap of the films deposited at optimized condition were found to be 0.20 eV and 1.22 eV, respectively. The absorption coefficient of the films was found to be 106 cm?1. Results prove that the lead sulphide films synthesized using spray technique appeal its adaptability for potential photovoltaic applications in solar cells. © 2017Item 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 Evaluation of semiconducting p-type tin sulfide thin films for photodetector applications(Academic Press, 2019) Barman, B.; Bangera, K.V.; Shivakumar, G.K.Tin sulfide (SnS) is an important semiconductor as it is one of the less common p-type materials with a bandgap of 1.53 eV which makes it an attractive material for photo detector application. In the thin film form, it is a sensitive photo conductor with attractive opto-electronic characteristics. In the current report, tin sulfide thin films have been deposited by thermal evaporation in vacuum and the influence of substrate temperature on its compositional, morphological, structural, and opto-electrical properties was studied. X-ray diffraction (XRD) study shows that all the thermally deposited films are having an orthorhombic crystal structure along (111) plane as pre-dominant orientation and are polycrystalline in nature. Raman analysis verify the occurrence of SnS and Sn2S3 phases in the films. Surface morphology along with the elemental composition of the films was determined by scanning electron microscopy (SEM) in combination with energy dispersive spectroscopy (EDS). All the films were found to be homogeneous, uniform, pin-hole free and have high optical transmittance in the UV–Vis wavelength region. The optical bandgap energy of the films was calculated using Tauc's relation and it was found to be decreasing (1.576 eV–1.429 eV) with increasing substrate temperature. The activation energy of the SnS thin films was calculated from Arrhenius plot and it was also found to be decreasing with increasing substrate temperature. The opto-electrical parameters such as photo conductivity (?L), dark conductivity (?D), response time (?r), recovery time (?d), photoresponsivity (R), and photosensitivity (S) were calculated and was found best for the films grown at 323 K. © 2019 Elsevier Ltd