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Preetha K.C.,Kannur University | Preetha K.C.,Symphony | Remadevi T.L.,Kannur University | Remadevi T.L.,Pazhassi Raja Nss College
Materials Science in Semiconductor Processing | Year: 2013

Lead sulfide (PbS) thin films were prepared on soda lime glass substrates at room temperature by Chemical Bath Deposition (CBD) technique. This paper reports a comparative study of characteristic properties of as-prepared PbS thin films after thermal treatment through two different routes. Studies were carried out for as-prepared as well as rapidly and gradually annealed samples at 100, 200 and 300 °C. The characterizations of the films were carried out using X-ray diffraction, scanning electron microscopy and optical measurement techniques. The structural studies confirmed the polycrystalline nature and the cubic structure of the films. As-deposited films partly transformed to Pb 2O3 when gradually annealed to 300 °C. The presence of nano crystallites was revealed by structural and optical absorption measurements. The values of average crystallite size were found to be in the range 18-20 nm. The variation in the microstructure, thickness, grain size, micro strain and optical band gap on two types of annealing were compared and analyzed. Data showed that post deposition parameters and thermal treatment strongly influence the optical properties of PbS films. Optical band gap of the film gets modified remarkably on annealing. Direct band gap energy values for rapidly and gradually annealed samples varied in the range of 1.68-2.01 eV and 1.68-2.12 eV respectively. Thus we were succeeded in tailoring direct band gap energies by post deposition annealing method. © 2012 Elsevier Ltd. All rights reserved.


Dhanya A.C.,Kannur University | Murali K.V.,Kannur University | Preetha K.C.,Kannur University | Deepa K.,Kannur University | And 3 more authors.
Materials Science in Semiconductor Processing | Year: 2013

Photo assisted chemical deposition method (PCD) is a new procedure for the deposition of compound semiconducting materials which is less explored. In this method the deposition is carried out with the irradiation of UV light on the reaction bath. PCD scores advantages for its low cost, use of flexible substrates and capability of large area deposition compared to other chemical methods like chemical bath deposition (CBD), electro chemical deposition (ECD), etc. Zinc sulfide films have been deposited on glass substrate by aqueous alkaline solution comprised of zinc nitrate, hydrazine hydrate, ammonium nitrate, ammonia and thiourea. The samples were prepared under UV illumination for different durations and characterized. The thickness of the samples increases with the deposition time. XRD patterns revealed the crystalline nature of samples with more number of dips. Optical study showed a low absorbance and constant transparency throughout the visible region disclosing the stiochiometric nature of the film. Obtained band gap energies were in good agreement with the theoretical value. Photoluminescence spectra showed two blue emission bands around 450 and 470 nm, and the intensity was found to depend on the thickness of the films. © 2013 Elsevier Ltd. All rights reserved.


Preetha K.C.,Kannur University | Preetha K.C.,Sree Narayana College | Remadevi T.L.,Kannur University | Remadevi T.L.,Pazhassi Raja Nss College
Physica B: Condensed Matter | Year: 2012

Doping of PbS thin films with different metal atoms produce considerable changes in structural and material properties that make them useful in the technology of thin film devices. The goal of this work is to study the effects of doping on the structural, morphological, optoelectronic and transport properties of PbS thin films as a function of Al 3 concentration. Thin films of pure and Al doped PbS nanoparticles are prepared on soda lime glass substrates by chemical bath deposition technique. The Al content in aqueous solution is varied from 0 to 20 mg. XRD analysis of the films revealed significant enhancement in crystallinity and crystallite size up to an optimum concentration of doping. Films are polycrystalline with crystallite size 19-32 nm, having face centered cubic structure. The optical band gap energy exhibits a decreasing trend and is shifted from 2.41 to 1.34 eV with increasing Al content. The room temperature conductivity of the as-deposited PbS films is in the range of 0.78×10 -8 to 0.67×10 -6( cm) -1 with a maximum for optimum Al content. The Al doped PbS thin film, which we synthesize with optimum Al concentration of 15 mg is found to be a most suitable material for solar control coating applications. © 2012 Elsevier B.V.


Remadevi T.L.,Kannur University | Remadevi T.L.,Pazhassi Raja Nss College | Preetha K.C.,Kannur University | Preetha K.C.,Sree Narayana College | Preetha K.C.,Symphony
Journal of Materials Science: Materials in Electronics | Year: 2012

Thin films of Lead sulphide (PbS) were grown on soda lime glass substrate by Successive Ionic Layer Adsorption and Reaction method from acidic, neutral and alkaline cationic precursor reaction bath by keeping the pH of the anionic precursor invariant. The structural and morphological aspects of the as prepared samples were investigated using XRD and SEM results. The as-prepared samples were polycrystalline with nanometer sized grains and identified as galena type cubic structure. The values of average crystallite size were found to be in the range 22-30 nm. The SEM micrographs show variations in morphology. Optical studies revealed the existence of both direct and indirect band gap with values in the range of 1.65-1.98 and 0.61-0.90 eV respectively. The room temperature conductivity of the PbS thin films were in the range 1.19 9 10-8-5.92 9 10-8 X cm-1. The optical band gap energy has inverse relation with grain size and electrical conductivity is closely related to structural parameters like grain size, crystallinity and micro strain. The estimated lattice parameter, grain size, optical band gaps, solid state and electrical properties were correlated with pH of the cationic solution. In this work, we establish that the pH of the cationic precursor media has colossal effect on the structural, morphological, optoelectronic, solid-state and electrical properties of PbS thin films. © Springer Science+Business Media, LLC 2012.


Preetha K.C.,Kannur University | Preetha K.C.,Sree Narayana College | Preetha K.C.,Symphony | Remadevi T.L.,Kannur University | Remadevi T.L.,Pazhassi Raja Nss College
Journal of Materials Science: Materials in Electronics | Year: 2013

An extensive study on the influence of metal ion sources on the properties of chemical bath deposited lead sulphide thin films is reported in this paper. Four different lead sources namely lead nitrate, lead acetate, lead chloride and lead sulphate in alkaline medium have been used for the synthesis along with thiourea as sulphur source. The influence of lead sources on structural, surface morphological optical and electrical properties is investigated for photovoltaic applications. According to X-ray diffraction studies, all the films are poly crystalline with face centered cubic structure. The average crystallite sizes are found to be in the range 13-24 nm. The SEM photographs showed diverse morphology. The optical band gap is found to be very sensitive to the metal sources used. The direct band gap energy values obtained are in the range of 1.862-2.609 eV. The electrical conductivity varies in the range 33.6 -7.62 × 10-9 (Ω cm)-1. Photosensitivity is closely linked to surface morphology. In this work, we established that the cationic precursor sources have significant role in physical properties of as-deposited PbS thin films. Samples prepared using nitrate as metal source are found to be most suitable to be used as solar control coating and the samples with lead acetate can be used as absorber layers for solar cell fabrication. © 2012 Springer Science+Business Media, LLC.


Preetha K.C.,Sree Narayana College | Remadevi T.L.,Pazhassi Raja Nss College
Materials Science in Semiconductor Processing | Year: 2015

Abstract Lead Selenide (PbSe) thin films have been deposited by Successive Ionic Layer Adsorption and Reaction (SILAR) method to investigate the effect of hydrazine hydrate on film properties. The peak behavior of the X-ray diffractogram corroborates crystalline nature of PbSe thin films. The intensity of the major peaks attributable to PbSe improved at higher concentrations up to 5 ml HH and gets reduced for 7 ml HH. The average crystallite size is in the range 18.18-33.37 nm. The film surface of lower HH sample is composed of spherical grains which are arranged in a compact manner. On increasing HH some clusters appears on the surface of the film over a homogeneous background. The AFM micrographs show that the surfaces of the lead selenide thin films consist of dense distribution of nanoscale particles with a range of grain sizes. The roughness obtained is in the range 13.7-76.3 nm. Highly crystalline sample, 5HH exhibits very good topography. The direct band gap values are in the range 1.425-1.803 eV. Thus by varying HH we have been able to tune the band gaps over a wide range. The highly crystalline sample 5HH with least strain and excellent topography exhibits maximum conductivity. © 2015 Elsevier Ltd.


Dhanya A.C.,Kannur University | Deepa K.,Kannur University | Deepa K.,Pazhassi Raja Nss College | Remadevi T.L.,Kannur University | Remadevi T.L.,Pazhassi Raja Nss College
Journal of Materials Science: Materials in Electronics | Year: 2013

Pure and Mn alloyed ZnS thin films have been prepared by UV accelerated chemical deposition technique which is simple, economic and easy to monitor. Influence of doping concentration on ZnS thin films was investigated through the structural, compositional, morphological, optical and luminescent studies. The XRD studies confirmed the formation of crystalline films with hexagonal structure. In doped samples the intensities of the prominent peaks increased up to 0.5 wt% Mn and then decreased. The optimum concentration means the amount required to get most suitable characteristics for photovoltaic application. The thickness of the films and the sizes of the crystallites varied in consistent with the structural results. Crystallites became larger in size on doping and appeared to be denser than undoped film. Various structural parameters like stress and micro strain were calculated. The observed strain is compressive in nature which rapidly increased with doping and then remained almost same with doping concentration. The SEM studies revealed the formation of films with almost similar morphology of spherical architectures. All the films exhibited uniform transmission in the high visible region, with a maximum of 80 % for the sample with optimum Mn concentration. Both direct and indirect band gap decreased due to the incorporation of Mn, but showed a blue shift in the fundamental absorption edge with doping concentration up to the optimum dopant content. Undoped and doped films exhibit five distinct luminescence peaks located around 391, 451, 458, 482 and 492 nm. The observed variation in the intensity of the luminescence in doped films clearly indicated the influence of thickness of the films which varied on doping. © 2013 Springer Science+Business Media New York.


Preetha K.C.,Sree Narayana College | Remadevi T.L.,Pazhassi Raja Nss College
Materials Science in Semiconductor Processing | Year: 2014

Undoped and Al doped lead sulfide (PbS) thin films were grown on soda lime glass substrates by Successive Ionic Layer Adsorption and Reaction (SILAR) deposition method. Al content in aqueous cationic solution was varied by adding 0.5-2% of aluminum nitrate in step of 0.5. The characterization of the film was carried out using X-ray diffraction, scanning electron microscopy, and optical and electrical measurement techniques. X-ray diffraction analysis revealed that both the undoped and doped films were polycrystalline and exhibited galena type cubic structure with average crystallite size in the range of 15.5-30.9 nm. The compositional analysis results indicated that Pb, S and Al were present in the samples. Optical studies revealed prominent blue-shift in the absorption edge of as-deposited samples upon doping as compared to that of bulk PbS and this shift was due to a quantum confinement effect. The room temperature conductivity of the PbS thin films was in the range of 1.343×10-7-1. 009×10-6 (Ω cm)-1for doped samples and 5.172×10-8 for undoped PbS thin film sample. The optical band gap energy has inverse relation with grain size and electrical conductivity is closely related to structural parameters like grain size, crystallinity and microstrain. The estimated lattice parameter, grain size, optical band gaps and electrical properties were correlated with Al concentration in the cationic solution. © 2014 Elsevier Ltd.


Preetha K.C.,Sree Narayana College | Remadevi T.L.,Pazhassi Raja Nss College
Journal of Materials Science: Materials in Electronics | Year: 2014

Lead selenide (PbSe) thin films have been synthesized by the established photochemical deposition technique using lead nitrate and lead acetate as sources for the metal ions and sodium seleno sulphate as the selenium source along with triethanolamine, ammonia and hydrazine hydrate as complexing agents. A comprehensive study of the effect of substrate materials on physical properties of as deposited PbSe thin films is reported in this work. Two substrates were used in this investigation, namely soda lime glass slides and gold coin corning glass slides. The solution is irradiated with UV light and the photochemical reactions in the aqueous solution resulted in highly adherent metallic thin films. X-ray diffraction (XRD), scanning electron microscopy, optical and electrical measurement techniques were used for film characterization. The XRD analysis confirmed that all films were cubic, regardless of the cationic precursors and substrates used. The scanning electron microscope micrographs showed variations in morphology. The optical studies revealed that the films have good absorption in the visible region. The remarkable success of our effort was that we have been able to modify optical band gap of PbSe thin films over a wide spectral range by a cost effective route. The band gaps estimated from the transmission spectra were in the range 1.32-1.40 eV for films deposited on soda lime glass substrates and 1.46-1.55 eV for corning glass substrates. The room temperature conductivity of the PbSe films were in the range of 3.71 × 10-7-513 × 10 -7 (Ω cm)-1. The as deposited PbSe thin films with low transmittance in the visible region coupled with an appreciable reflectance in infrared region were found to satisfy the basic requirements for solar control coatings for window glazing applications in warm climates. Through this work we established that irrespective of metal salts, soda lime glass substrate was superior to corning glass substrate. © 2014 Springer Science+Business Media New York.


Preetha K.C.,Kannur University | Preetha K.C.,Sree Narayana College | Murali K.V.,Kannur University | Murali K.V.,Nehru Arts and Science College | And 6 more authors.
Current Applied Physics | Year: 2012

The lead sulfide (PbS) thin films were deposited on glass substrate using successive ionic layer adsorption and reaction (SILAR) method at different pH of the cationic precursor, keeping the pH of the anionic precursor invariant. In this work, we establish that the pH of the cationic precursor and in turn the size of the crystallites affects the optical and electrical properties of PbS thin films. The characterization of the film was carried out using X-ray diffraction, scanning electron microscopy, optical and electrical measurement techniques. The presence of nanocrystallites was revealed by optical absorption and structural measurements. The PbS thin films obtained under optimal deposition conditions were found to be polycrystalline with face centered cubic structure. The lattice parameter, grain size, micro strain, average internal stress and dislocation density in the film were calculated and correlated with pH of the solution. The values of average crystallite size were found to be in the range 16-23 nm. Optical studies revealed the existence of direct and indirect band gap values in the range 0.99-1.84 eV and 0.60-0.92 eV, respectively. The room temperature resistivity of the synthesized PbS films was in the range of 1.2 × 107 to 3.5 × 107 cm. © 2011 Elsevier B.V. All rights reserved.

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