Radiation Effect on the optical& structural properties of CdTe: Zn thin Films @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹1a26@@ÖÜ»€a@I2@‚b«@H2013 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 26 (2) 2013 Radiation Effect on the Optical& Structural Properties of CdTe: Zn thin Films Suad I. Issa Dept.of Physics/College of Education For Pure Science (Ibn Al- Haitham)/ University of Baghdad Received in : 29 May 2012 , Accepted in : 16 April 2013 Abstract The Films of CdTe:Zn were prepared on a glass by using vacuum vapor deposition technique .The x-ray diffraction pattern revealed that the films have polycrystalline with FCC structure and the preferred orientation was along (111) plane. The films were exposed to a low dose of gamma ray.(5µCi for 30 days) Transmission and absorptance spectra were recorded in the range of (400-1100) nm before and after irradiation. It was found that irradiation has a clear effect on the optical and structural properties which include the transmition and absorption spectra, extinction coefficient, refractive index, and the energy gap. Keywords: CdTe thin films , Vacuum Evaporation , XRD 150 | Physics @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹1a26@@ÖÜ»€a@I2@‚b«@H2013 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 26 (2) 2013 Introduction CdTe has emerged as a promising thin film material for a number of reasons. Thin films of CdTe are usually p-type semiconductors, but can be made both p-type and n-type.[1] Its 1.5eV direct band gap is nearly ideal for terrestrial energy conversion. It has a very high absorption coefficient, meaning that relatively thin layers can be used to make functional devices.[2] CdTe is an important II -VI semiconductor material, which is very useful for a variety of electro-optical devices and solar energy conversion [3-4]. The theoretical limit of conversion efficiency for polycrystalline CdTe is 29%.[5] By 1982, Kodak researchers Tyan and Perez- Albuerne had produced the first cell with 10% efficiency.[2] Having a large exciton Bohr diameter (15.0 nm), and its high absorption coefficient (~105 cm- 1) [4]. There are some rearranged reports about the deposition methods available for the preparation of CdTe thin films such as close spaced sublimation (CSS), physical vapor deposition (PVD), vacuum evaporation, vapor transport deposition (VTD), closed space vapor transport, electrodeposition, screen printing, spray pyrolysis, metalorganic chemical vapor deposition (MOCVD), and RF sputtering.[6]The aim of the work is to study effect of X-ray and gamma ray on the optical and structural properties of the CdTe:Zn films. Experimental CdTe thin films were deposited on to well-cleaned glass substrates by physical vapor deposition technique. The samples under study were prepared using the following deposition parameter: the source (evaporator), substrate distance was (10cm) , source temperature was 300K ,and the films were deposited under a pressure of 3×10-5 mbar[7-8]. the films thickness was determined by the weight method from the equal : 𝑡 = ∆𝑚 𝜌𝐴 (1) where: t : thickness ∆m: different between the weight and the weight substrate before and after the film deposition. ρ: density of the material deposition (gm/cm3) A: substrate area (cm2). All films had nearly about or equal to thickness (500nm). The optical and absorption measurement were recorded using one beam (UV-Visible 1800 spectra photometer) in the 400-1100 wavelength. The thin film CdTe:Zn with two percent deposited 2% was radiation by gamma ray from CO60 5µci within 30 days, after that the transmition and absorption spectra were recorded and we studied the effect of radiation on the optical and structural properties. Structural properties The prepared sample CdTe:Zn thin films on thin glass slides substrates reveal that the nature of the structures of films were polycrystalline and typed cubic [9].Applying Brag's Law using (hkl Miller indices) these faces are in agreement with (ASTM) standards card as well as previous studies[10-11] .Figures (1),(2) show the x-ray diffraction spectra (CdTe:Zn) before and after irradiation .Fig(1) clarifies strong diffraction peaks at (23.5˚,25.5˚) it is before irradiation and Fig(2) clarifies strong diffraction peaks only at(23.5˚) after irradiation . 151 | Physics @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹1a26@@ÖÜ»€a@I2@‚b«@H2013 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 26 (2) 2013 Results and Discussion By studying optical properties (transmission and absorption spectra, refractive index dispersion) of CdTe:Zn films, information can be obtained about energy band-gap , characteristics of optical transitions , etc.[5] The optical transmission spectra before irradiation as a function of wavelength in the range of (400-1100)nm is shown in Fig(3) for CdTe:Zn The ratio of deposition was 2% it is obvious from the Figure that CdTe:Zn has a larger transmittance for wavelength 270 nm. The CdTe:Zn film after irradiation is decreased with transition which indicates the increment with absorbance. The absorbance of the films as a function of wavelength is presented in Fig(4) the absorbance spectra before irradiation is increased with wavelength and after irradiation decreased with absorbance in visible range (500-700)nm. The extinction coefficient k was calculated from the relation [12]. k =𝛼ג 4𝜋 (2) Where: α: Absorption coefficient. .wavelength for the incident light :ג It could be noticed that k before irradiation increases in 2.9eV and after irradiation is decreased and it is shown in Fig (5). The refractive index was calculated from the relation [13] n= [ (1+𝑅)² (1−𝑅)² −k ² +1]½ − 1+𝑅 1−𝑅 (3) Where: R: Reflectance and calculated with the relation [14] R=1-A-T (4) Figure (6) depicts the variation of refractive index with photon energy for films. Therefore the refractive index decreases after irradiation from (20.1) to (9.2) and shift in energy gap from a value of (1.8eV) to a value of (1.6eV). Fig (7) and Fig (8) clarifies the relation between (αhν)² and hν. The relation between absorption α and the incident photon energy hν can be written as [15] αhν=C1 (hν-Eig )² ,indirect transition (5) αhν=C2 (hv-Edg )1/² ,direct transition (6) where C1 and C2 are constants Eig is the indirect transition band gap energy Edg is the direct band gap. The (αhν)2 are plotted against the photon energy (hν) the intercept point with the energy axis gives the edge of the allowed direct transition. It has been observed that direct band gap energy increased before irradiation was (1.6eV) and the value of the after irradiation decreased to (1.58eV). Conclusions It was found that irradiation has a clear effect on the optical and structural properties by studying optical properties (transmission and absorption spectra , refractive index dispersion) of CdTe:Zn films. 152 | Physics @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹1a26@@ÖÜ»€a@I2@‚b«@H2013 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 26 (2) 2013 References 1. Kazmerski ,( 2002), L. L. 29th IEEE PhotoVoltaics Specialists’ Conf., 21. 2. Ali,A. ;Shah, N. A. ; Aqili ,A. K. S. and Maqsood , A. (2006 ) , Impact of Evaporation Rates of Cd and Te on Structural, Morphological, Optical, and Electrical Properties of CdTe Thin Films Deposited by a Two-Sourced Evaporation Technique , Crystal Growth & Design , 6 (9) : 2149 - 2154 . 3. Tan, G. L. ;Wu, N. and Zheng, J. G. ( 2006), Optical absorption and valence band photoemission from uncapped CdTe nanocrystals.” J Phys Chem B. 110: 2125. 4. Becerril, M. ; Zelaya-Angel, O. , and Vargas-Garcia, J. R. ( 2001), J Phys Chem Solids , “Effects of Cd vacancies on the electrical properties of polycrystalline CdTe sputtered films.” J Phys Chem Solids , 62: 1081. 5. Kolosov,S. A.; Klevkov,Yu. V., and Plotnikov ,A. F. ,(2004), Electrical Properties of Fine- Grained Polycrystalline CdTe, Semiconductors, 38 (4): 455 – 460. 6. Kumaravel ,R. and Krishnakumar , V. ( 2010), Effect of annealing on the electrical, optical and structural properties of cadmium stannate thin films prepared by spray pyrolysis technique, Thin Solid Films, 518 : 2271–2274. رسالة ماجستیر، Znالمشوبة بـ CdTeْالغشیة دراسة الخواص التركیبیة والبصریة ، )2011سرمد مھدي (علي ، .7 ./ ابن الھیثم ، جامعة بغداد للعلوم الصرفة كلیة التربیة 8. Misho, R. H. and Murad, W. A. (1992) Solar Eneryy Mats, And solar cells state comm. 27:335-340. 9. Yousif , M.G. (1989) solid state physics , Vol.1,University of Baghdad book. 10. Srinrasa Murty,N.and Jawalekar,S.R. (1983) Thin Solid Films,100 :219-225 11. Zhengtian Gu , Peihui Liang , Xiaolin , and Weiqing Zhang , Anovelsen , (2000) scheme of determining the optical parameters of the thin films by polarized reflect Meas.Sci Tch., 11 (4):(56-61) 12. Marque , E, Ewen ,P. and Owen , A. (1992) , J.phys.D.Appl.Phys, 25:535. 13. Donald ,N.A, (1992) semiconductor physics and Devices, University of New Mexico. 14. Khashan ,M.A. and Naggar , A.M.Al, (2000) , Optics communications , 174:445. 15. Padmanabha Sharma , H , Subramanian , V, Rangarajan , N. and Murali ,k.R. (1995) , Bull.Mater.Sci, 18 , 875. Fig (1): X-ray diffraction before irradiation 0 500 1000 1500 2000 2500 3000 3500 4000 20 30 40 50 60 70 tn te ns it y (a .u .) 2θ 153 | Physics @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹1a26@@ÖÜ»€a@I2@‚b«@H2013 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 26 (2) 2013 Fig (2): X-ray diffraction after irradiation Fig. (3) :Transmittance as a function with wavelength 154 | Physics @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹1a26@@ÖÜ»€a@I2@‚b«@H2013 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 26 (2) 2013 Fig. (4): Absorbance as a function with wavelength Fig. (5): Extinction coefficient as a function of photon energy Fig. (6) Refractive index as a function of photon energy 155 | Physics @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹1a26@@ÖÜ»€a@I2@‚b«@H2013 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 26 (2) 2013 Fig. (7) (αhv)² as a function with photon energy (before irradiation) (α hν )² Photon energy (eV) Fig. (8) (αhv)² as a function with photon energy (after irradiation) (α hν )² Photon energy (eV) 156 | Physics @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ÚÓ‘Ój�n€a@Î@Úœäñ€a@‚Ï‹»‹€@·rÓ:a@Âig@Ú‹©@Ü‹1a26@@ÖÜ»€a@I2@‚b«@H2013 Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 26 (2) 2013 الخواص البصریة والتركیبیة الغشیة تیلراید الكادمیوم فياثیر التشعیع ت المشوبة بالزنك عیسى سعاد عمران جامعة بغداد / )أبن الھیثم( للعلوم الصرفة كلیة التربیة/الفیزیاء علوم سم ق 2013نیسان 16، قبل البحث 2012آیار 29أستلم البحث الخالصة حضرت اغشیة تیلراید الكادمیوم الرقیقة المشوبة بالزنك باستخدام تقنیة التبخیر الحراري في الفراغ على قواعد من بلور وامتالكھا تركیب مكعب تال ةالزجاج. ظھر من طراز حیود االشعة السینیة لالغشیة المشوبة قبل التشعیع انھا متعدد FCC ضت ھذه االغشیة لجرعة من اشعة كاما 111 )(وباتجاھیة یوماً، سجل طیف النفادیة 30مدة 5µCiُعرِّ في. لقد وجد ان التشعیع قد اثر وبشكل واضح وبعده ) لھذه االغشیة قبل التشعیعnm)400-1100 واالمتصاصیة من مدى الخواص البصریة والتركیبیة والمتضمنة طیفي النفادیة واالمتصاصیة، معامل الخمود، معامل االنكسار، وفجوة الطاقة المحظورة. حیود االشعة السینیة، التبخیر الفراغيالنقیة ، CdTeأغشیة الكلمات المفتاحیة: 157 | Physics