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 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 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 Bi doping on the properties of CdSe thin films for optoelectronic device applications(Elsevier Ltd, 2017) Santhosh, T.C.M.; Bangera, K.V.; G.k, S.CdSe and Bi (1%, 2%, 3%) doped CdSe thin films were deposited on the glass substrates using thermal evaporation technique. Effect of Bi doping on the structural, optical, electrical and photo response properties of CdSe thin films were investigated. The X-ray diffraction studies reveals that undoped and Bi doped CdSe films are polycrystalline in nature with hexagonal crystal structure along (002) direction. No significant changes are observed in the lattice parameters or the grain size indicating minimum lattice distortion. The optical band gap of undoped CdSe film was estimated to be 1.67 eV. Replacement of cadmium by bismuth results in an increase in the electrical conductivity of doped films. Doping with bismuth is found to improve the photo sensitivity of CdSe thin films. © 2017 Elsevier LtdItem Effect of Ag in CdSe thin films prepared using thermal evaporation(Maik Nauka-Interperiodica Publishing, 2017) Santhosh, T.C.M.; Bangera, K.V.; Shivakumar, G.K.It has been a general practice to dope thin films with suitable dopants to modify the properties of the films to make them more suitable for potential applications. When the dopant concentrations are low, they do not normally affect the structure and morphology of the films. However, it may lead to drastic changes in electronic properties of the films. This might result from the dopant getting incorporated into the lattice of the material of the films. Cadmium selenide is an important compound semiconductor material with an attractive energy band gap. The present work relates to an attempt made to dope CdSe thin films with silver. CdSe:Ag (1–5%) thin films were deposited on glass substrates at an optimized substrate temperature of 453 K using thermal evaporation technique. The grown films were analyzed using X-ray diffraction, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDX) techniques. It is observed that undoped CdSe thin films and CdSe:Ag films have hexagonal structure. The grain size was found to increase marginally with an increase in the Ag concentration. The optical band gap of the films determined by optical transmission measurements agree with that of CdSe. Electrical conductivity is observed to increase from 10–4 to 3.66 (? cm)–1 on addition of silver. The variation of resistance with temperature indicates that the prepared films consist of CdSe and Ag existing as two separate phases coexisting and contributing individually to the resistivity of the films. © 2017, Pleiades Publishing, Ltd.