Research Journal of Engineering Sciences _________________________ ______ ____ ________ ISSN 2278 – 9472 Vol. 2 ( 7 ), 1 5 - 1 9 , Ju ly (201 3 ) Res. J. Engineering Sci. International Science Congress Association 15 Growth and Characterization of Lead Selenide (PbSe) Thin Fi lm, by Chemical Bath Deposition Isi P. O 1 ., Ekwo P. I. 2 1 Department of Physics, Paul University Awka, Anambra State, NIGERIA 2 Department of Physics and Industrial Physics, Nnamdi Azikiwe University, Awka, Anambra State , NIGERIA Available online at: www.isca.in Received 12 th June 201 3 , revised 23 rd June 201 3 , accepted 20 th July 201 3 Abstract Lead Selenide (PbSe) thin film has been grown on glass slides by Chemical Bath Deposition method at 300k. Characterization of optical and structural properties of the films were carried out using a Jane way 6405 UV - VIS Spectrophotometer and an X - ray mini - d iffraction (MD - 10) using Cukα radiation with λ = 1.5406 nm . The absorbance of the deposited films was high while the transmittance was almost zero within the visible and infrared regions of electromagnetic spectrum. The optical band gap of the deposited f ilm was found to be 0.28eV. The deposited thin films of Lead Selenide were found to be polycrystalline in nature. XRD studies reveals cubic structure with preferred orientation along (200) plane. The lattice constant was found to be 5.84Å. Keywords: Lead Selenide, Chemical bath, Thin films, Optical and structural properties . Introduction Metal chalcogenides compounds, have semiconducting properties for which reason they are for technical interest in the production of electronics and electro - optical devices. For past years, research works have been carried out on the fabrication and characterization of these compounds in the form of thin film 1 . Lead Selenide thin film has motivated many researchers due to its application in solar cell technology 2 - 6 . There exist many methods for the deposition of PbSe thin films which were reported in the literature, these deposition methods are of two categories; chemical and physical deposition methods. Examples of chemical d eposition methods are chemical bath deposition (solution growth technique), spin coating deposition, atomic layer deposition etc. while the physical deposition methods are sputtering deposition, electro spray deposition, cathodic arc deposition etc 7 - 15 . L ead Selenide thin films are mostly used as a major material in infrared sensor, grating, photo resistor, lenses and various optoelectronic devices 16 - 18 . In this paper, optical and structural properties of PbSe thin film prepared by chemical bath deposition method at 300k are presented. Material and Methods The films used for this experiment were synthesized by chemical bath deposition (CBD) method. The chemical reaction for the deposition of PbSe thin film was based on the reaction between lead acetate {( CH 3 COO) 2 Pb. 3H 2 O)} as the source of lead ions, EDTA Di Sodium salt as the complexing agent, Selenium sulphate (SeSO 4 ) as the source of selenium ions, and Ammonia (NH 3 ) as pH adjuster at 300k. In this experiment, five chemical reaction baths (50mls beakers ) were used. 5mls of lead acetate was measured into a 50ml beaker using burette; 2mls of EDTA was then added and stirred gently to achieve uniform mixture. The reaction is exothermic. 5mls of selenium sulphate was then added, 2mls, 4mls, 6mls, 8mls and 10m ls of ammonia solution were then added to the mixtures in the reaction baths respectively. The mixtures were then topped with distilled water to 50mls mark and stirred to achieve uniform mixture. A glass substrate was dipped vertically into all of the five reaction baths. The baths were left to stand for 24 hours (as indicated in Table 1) after which the substrates were removed after 24 hours, rinsed with distilled water and dried in clean air. The slides were observed to have been coated with thin films. T he optimal parameter was found to be pH of 10.38. The optical characterization of PbSe thin films was done using Janeway 6405 UV - VIS model of spectrophotometer while the X - ray mini - diffraction (MD - 10) using Cukα radiation with λ = 1.5406 nm was used to s tudy the structural properties. Chemical equations for the deposition are: (CH 3 COO) 2 Pb .3H 2 O+EDTA↔[Pb (EDTA)] 2+ +2(CH 2 COOH) + 2 (OH) - +H 2 O Pb(EDTA) 2+ ↔ Pb 2+ + EDTA SeSO 4 + 2(OH) - ↔ SO 4 2 - + (OH) 2 Se (OH) 2 Se + 2(OH) - ↔ Se 2 - + 2H 2 O+O 2 PbS + + Se 2 - ↔ PbSe Results and Discussion Figure - 1 and 2 shows the plots of transmittance and absorbance as a function of wavelength (λ) for PbSe thin film. The transmittance spectra displayed in figure - 1, shows vibration of atomic constituent of PbSe in U V region and zero transmittance was shown in Vis and Infrared region of electromagnetic spectrum, while high absorbance was observed within visible Research Journal of Engineering Sciences ___________ _________ _____ __________________ ______ ____ ___ ISSN 2278 – 9472 Vol. 2 ( 7 ), 1 5 - 1 9 , Ju ly (201 3 ) Res. J. Engineering Sci. International Science Congress Association 16 and infrared regions of electromagnetic spectrum, hence the films can be used in fabrication of solar cells and also be for spectral selective windows and diachronic mirrors. Table - 1 Variation of pH for 24 hours for PbSe thin film Volume of reagents used (mls) Reagents used Slide 6 Slide 7 Slide 8 Slide 9 Side 10 (CH 3 COO)Pb.3H 2 O 5 5 5 5 5 EDTA 2 2 2 2 2 SeSO 4 5 5 5 5 5 NH 4 2 4 6 8 10 Distilled H 2 O 36 34 33 30 28 pH value (no unit) 9.34 9.37 9.96 10.14 10.38 Figure - 1 Transmittance as a function of wavelength (λ) for PbSe thin film Figure - 2 Absorbance as function of wavelength (λ) for PbSe thin film Research Journal of Engineering Sciences ___________ _________ _____ __________________ ______ ____ ___ ISSN 2278 – 9472 Vol. 2 ( 7 ), 1 5 - 1 9 , Ju ly (201 3 ) Res. J. Engineering Sci. International Science Congress Association 17 Figure - 3 Absorption coefficient (α) as function photon energy (hν) for PbSe thin film Photon energy hν (eV) Figure - 4 Square root of absorption coefficient (α 1/2 ) as a function of photon energy (hν) Figure - 4 shows p lot of square root of absorption coefficient (α 1/2 ) as a function of photon energy (hν), which gives the intercept of the inverted curve with the photon energy axis, when α 1/2 = 0 gives the band gap of 0.28eV. Figure - 5 shows a plot of reference slide (a clean slide that has no deposition on its surface), which has no prominent peak because there was no deposition on it, and this confirms that glass is amorphous in nature. Figure - 6 shows prominent peak in 2θ values which correspond to (200) plane and oth er peaks at different 2θ values which also correspond to (220) and (111) planes respectively. The film is polycrystalline in nature due to the presences of the peaks 20 . The predominant growth of crystallites perpendicular to (200) plane gave rise to the cl austhalite cubic structure with lattice constant 5.84Å and is in close agreement with Okereke 21 . The predominant orientation in the (200) plane has been reported by Prabahars 22 . Research Journal of Engineering Sciences ___________ _________ _____ __________________ ______ ____ ___ ISSN 2278 – 9472 Vol. 2 ( 7 ), 1 5 - 1 9 , Ju ly (201 3 ) Res. J. Engineering Sci. International Science Congress Association 18 Figure - 5 X - ray spectra for uncoated slide (control slide) Figure - 6 X - ray spectra for coated slide at 300k Research Journal of Engineering Sciences ___________ _________ _____ __________________ ______ ____ ___ ISSN 2278 – 9472 Vol. 2 ( 7 ), 1 5 - 1 9 , Ju ly (201 3 ) Res. J. Engineering Sci. International Science Congress Association 19 Figure – 7 XRD diffrac tion pattern for PbSe thin film Conclusion Thin films of Lead Selenide were successfully grown on glass slides by chemical bath deposition method. The reaction bath was formed with the solutions of (CH 3 COO) 2 Pb.3H 2 O, SeSO 4 , EDTA and NH 3 in 50mls beaker. PbSe thin films were found to have zero transmittance within visible and infrared region of electromagnetic spectrum while the absorbance was high within VIS and decr eased a little within infrared regions of electromagnetic spectrum. It therefore provides an opaque coating on glass which can be applied for thermal window glass coating. It also can be used in fabrication of solar cells. The energy band gap was determine d to be 0.28eV. Structural characterization reveals that the films are crystalline of cubic structure. The relative intensity was maximum at 2θ = 29.1406 0 corresponding to the (200) plane. The lattice constant was calculated to be 5.84Å. 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