ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Hai tham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 Annealing Effect on the Optical Properties of (ZnO)x(CdO)1-x Films Obtained by Spray Pyrolysis W. H. Abass Departme nt of Science , College of Basic Education, Unive rsity of Al- Mustansiriyah Received in: 7 April 2011, Accepte d in: 20 September 2011 Abstract The effect of the annealin g on the op tical transmission , absorp tion coefficient, dielectric constants (εr),( εi) ,Skin depth and the optical ener gy gap of (ZnO)x(CdO)1-x thin films with (x=0.05) deposited on p reheated glass substrates at a temp erature of (450 C°) by chemical p y roly sis technique were p erformed . These f ilms show direct allowed inter band transition that influenced by annealing at ( 450 C°) for two hours . And it also found that the optical ener gy gap has been increased fro m about (2.50 eV) b efore annealing to about (2.65 eV) after annealin g , fro m the analy sis of the absorp tion and transmission sp ectra in the wavelength range (380-900nm) . The results show that all these parameters were affected by annealin g. Key words: (ZnO)x(CdO)1-x thin film, op tical p rop erties, Chemical Sp ray py roly sis, annealin g effect Introduction Transp arent conducting oxide (TCO) thin films have been widely used in solar cells applications. CdO and ZnO have high transp arency in the visible region of the electromagn etic sp ectrum and show n-type conductivity , mainly due to oxy gen vacan cies[1]. Cadmium o xide is an oxy gen deficient n- type conducting due to oxy gen vacancies [1], and has NaCl structure [2]. Cadmium oxide has been consider ed as a p romising material for solar cells [3] , due to high electrical conductivity and its high transp arency in the visible region, also for these p rop erties , CdO could be used as a gas sensor , low-emissivity windows, wear resistant app lications, flat p anel disp lay s , Thin film resistor, light emitt ing diode ,heat reflectors [4-7]. ZnO materials have received broad att ention due to their well-known p erformance in electronics, op tics and p hotonics. The interest in dop ing ZnO is to exp lore the possibility of tailorin g its electrical, magnetic and op tical p rop erties. Zinc oxide can be dop ed with a wide variety of ions to meet t he demands of several app lication fields [8]. Z nO can be found easi ly as n-type because of Zn interst itials and oxy gen v acancies. Recently, the dop ing of different elements has been att emp ted to induce new interesting p rop erties, such as for transp arent electrodes [9]. For the development of optoelectronic devices with ZnO, it is necessary to have high quality materials of bot h n-type and p -type. we report the effect of annealing at (450 ºC) on the optical p rop erties of (ZnO)x(CdO)1-x grown by sp ray py roly sis. Experime ntal De tails Thin films of (Z nO)x(CdO)1-x have been p rep ared by chemical py rolysis technique ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Hai tham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 The sp ray py rolysis was done with a laboratory design ed glass atomizer, which has an outp ut nozzle about 1 mm. The films were dep osited on p reheated glass substrates at temp erature of 450°C, the chemical solution was achieved by addin g 2.974 gm of (Zn (NO3)2 6H2O) on 100 ml of distilled water , and adding of 3.0847gm of (Cd(NO3)24H2O) on 100 ml of distilled water by using magnitin g st irrer achieved by taking 0.1 M of dissolve in distilled water as equations[9]: )..................... 1000 (1 VMwt Wt M  Where: M: Concent rat ion mol. Mwt : Mo lecular weight from (Zn (NO3)2 6H2O) an d (Cd(NO3)24H2O). Wt: want ed weight dissolved in dist illed wat er. V: Vol ume of dist illed wat er. The opt imized condit ions were the following paramet ers, spray t ime (15 sec) and t he spray interval (2 min) , average deposit ion (10 cm 3 /min ) , distance between nozzle and substrat e ( 30 cm) and t he carrier gas (filt ered compressed air) was maint ained at a p ressure of 10 5 Nm -2 . Thicknesses of t he samples were measured using the weight ing method. The accuracy of t hickness measurements was (750 nm) These films were annealed at (450 ºC ) for t wo hours , Optical t ransmitt ance and absorbance were recorded in the wavelength ran ge (380-900nm) using UV-v isible spect rophotom et er (Shimadzu Comp any Japan). Results and Discussions Fig. (1) shows t he sp ectral distribution of transmittance for the as dep osited and annealed (ZnO)x(CdO)1-x films at (450 °C) in the wavelength range (300-900) nm. In this sp ectral region, transmittance of annealed (ZnO)x(CdO)1-x film is h igher than that for as deposited on. The increasin g of transmission for (ZnO)x(CdO)1-x might be due to decrease scatt ering of p hotons by crystal defects, and the free carr ier absorp tion of p hotons contributed to the reduction in op tical transmittance, or might be du e to increase of the crystallite size. The increased rou ghness of the annealed thin films contributed to the drastic decrease of op tical transmittance [10], From this figure it is observed that the transmittance decreases at the low wavelength region, which is the sp ectral region of fundamental absorption, in this region the inco min g p hotons have sufficient ener gy to excite electrons from the valence band to the conduction band and thus these p hotons are absorbed within the material to decr ease the transmittance. For this reason, this region carries the information of the band gap of the material [11]. Figure (2) shows the absorption coefficient (α) of annealed and as deposited (ZnO)x(CdO)1-x films versus p hoton energy , from this fi gure α (annealed (ZnO)x(CdO)1-x ) > α (as deposited (ZnO)x(CdO)1-x), this might be att ributed to the increase of defect st ates which leads to incr ease absorp tion coefficient. Absorption of p hotons creates electron-hole p airs. In turn, the field of such p airs may modify the elect ronic structure and hence of optical propert ies of (ZnO)x(CdO)1-x film [12]. According to the solid band t heory , the relation bet ween the absorpt ion coefficient an d t he energy of incident light is given by (αhf) n =B(hf-Eg) [13] , in which B is a constant ,Eg is the op tical band gap energy and n is the ½ and 2 for the allouued transition bein g indir ect and direct ,resp ectively . ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Hai tham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 Figure (3) shows a p lot of (αhf) 2 as a function of photon energy .The direct (n=2) band gap value of annealed and as deposited(ZnO)x(CdO)1-x films are d etermined fro m the curve extrapolation. These valu es are 2.65 e V and 2. 50 eV resp ectively . This may be the cause for the decrease in b and tail width, and then increase energy gap. Refractive index is one of the fundamental p rop erties for an op tical material , because it is closely related to the electronic polarizability of ions and the local field inside materials. The refractive index (no) is related to the op tical reflectance (R) by the following relation [14]: (1) -------------                   1 1 )1( 4 2/1 2 R R K R R n o Where (K) is the extinction coefficient. The behavior of refractive index is nearly similar to the reflectance , the refractive index increases with annealing ,We can observe from Fig.(4) ,The decrease in refractive index could be attributed to the decrease of optical absorp tion in this range. The extinction coefficient (k°) can be determined by using the relation [15]: (2) -------------    4 k o Where is the absorp tion coefficient and (λ) is the wavelength of the incident p hoton. Figure (4) Shows the variation in (k°) as a function of the Phot on energy , It can be noticed that the extinction coefficient increases with annealing. The variation of the real (r) and imaginary (i) p arts of the dielectric constant values versus Photon energy for (ZnO)x(CdO)1-x films before and after annealing are shown in Figure (5). The behavior of r is similar to t hat of refractive index because the smaller valu e of( k° 2 ) comp ared with (n° 2 ) [16]: εr = n° 2 -k° 2 ------------(3) while (i) is mainly depends on the (k°) values, which are related to t he variation of absorp tion coefficient [16]: εi =2n° k°-------------(4) The variations of these two p arameters with incident p hoton energy were shown in Figure (5). From these curves It is found that r and i increases after annealing. The real and imaginary p arts of the dielectric constant indicate the same p att ern and the values of real part are higher than imaginary p art [16]. It is useful to define a characteristic ‘‘skin’’ thickn ess that is subject to an app reciable density of optical ener gy .A convenient form used widely is simply the inverse of α, i. e. χ ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Hai tham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 = 1 / α . In other words, t he electromagn etic wave will have amp litude reduced by a factor 'e' after traversing a t hickness (called t he skin depth) [17] . The behaviors of the curves in Figure (6) can be divided in t o two part s . In the first region below λ=440 nm, skin dept h decreases wit h annealing . While for the secon d region higher than λ=440 nm ,the skin depth increases wit h annealing as compared wit h t he depo sit ed on. due to increase the pro bability of absorpt ion wit h annealing. Conclusions (ZnO)x(CdO)1-x thin films were deposit ed ont o glass subst rat es heat ed at 450C 0 , by chemical pyroly sis t echnique . T he heat treat ment ch anges t he opt ical charact erist ics under invest igat ion in this study. T he result sho w t hat the Eg is (2.50 eV) before ann ealing an d (2.65eV) aft er annealing. Re ferences 1. Boeeze, A. and p erkins, P.G. (1973), solid st ate p hy sics , Cadmium Oxide (CdO) Opt ical and photoelectric ,dielectric constants, 13, 1031. 2. Altwein, M .; Finkenrath, H.; Konak, C.; st uke, J. and Zimmerer, G. (1968), solid st ate p hy sics The Electronic Structure of CdO II. Sp ectral Dist ribution of Optical Const ants, 29, 203. 3. Vigil ,O. ; Vaillant, L. ; Cruz, F.; Santana, G.; M orales-Acevedoc, A.and Contreras- Puente G., (2000) Thin Solid Films 361–362, 53. 4. M artin, E.; Yan, M . ; Lane, M . ; Ireland, J. ; Kann ewurf ,C. and Chang ,R.H. (2004), T hin Solid Fi lms 461, 309. 5. Carballeda-Galicia, D.; Castanedo-Pérez , R.; Jiménez-Sandov al, O.; Jimén ez – Sandoval, S.; Torres-Delgado, G.; C. Zúňi ga-Romero, (2000) ,Thin Solid Films 371 , 105 . 6. Kim, H. ; Gilmor e , C.M . ; Pique, A. ; Horwitz , J.S. ; M att oussi , H. ; M urata , H. ; Kafafi ,Z.H.; Chrisey, D.B., J. (1999) , solid st ate p hy sics ," Electrical, op tical, and st ructural p rop erties of indium–tin–oxide thin films for or ganic light-emitting devices". 11 ,6451. 7. Anandan , S., Curr. ,(2008) , Ap p l. Phys. 8 , 99. 8. Seeber, W. T. ; Abou-Helal ,M . O. ; Barth, S. ; Beil , D. ; HoÈ che, T. ; Afify , H. H. and Demian , S. E., (1999) , M aterials Science in Semiconductor Processin g ,"Transp arent Semiconducting ZnO:Al Thin Films Prep ared by Sp ray Py roly sis", 2 , 45-55. 9. Jeung Hun Park, Hy uk K. Pak and Chae-Ry ung Cho, (2006) , Journal of the Korean Physical Society , Dep osition-Temp erature Effects on AZO Thin Films Prep ared by RF M agnetron Sputtering and Their Phy sical Prop erties, 49, 584- 588. 10. Tigau , N. ; Ciup ina ,V. ; Prodan, G. ; Rusu ,G. I. ; Gheorghies ,C. and Vasile, E. (2003) Opt oelectronics Advance M aterials , Structural, optical and electrical p rop erties of Sb2O3 thin films with different thickness , 8 , 1 37-42. 11. Banerjee1,A.N. ; Ghosh ,C.K., Das , S. ; Chatt op adhy ay , K.K., (2005)..Phy sica B 370, 264–276. 12. Afaf Abdel-Aali, Bahiga Abdel-Hameed M ansoour, Hoda M ohamed EISSA3,(2005) T urk J. Phy s, Some Phy sical Prop erties of g Irradiated Gex(As2Te3)100 - x Chalcogenide Sy st em,. 29 ,223 - 232. 13. Balitska, V. O. ; Shp oty uk ,O. I., (1998) , Non-Cryst Solids ,"On the problem of electron- induced an isotropy effect in As2S3-based glasses" , 227, 723. 14. Ezekoy e, B. A. ; Okkek ,C. E., (2006) ,The Pacific Journal of Science and Techno logy , 7,108. 15. Chinese journal of p hysics(2007), 45, 2-I APRIL . 16. Shokr, E. K. ; Wakkad, M . M . ; M ater, J., (1992), Sci. Effect of laser irradiation on the optical p rop erties of amorphous Se96-xTe4Gax thin films , 27, 1197. 17. Eloy J. F. (1984), National School of Physics, Power Lasers , Grenoble, France, John Wiley & Sons , 59. ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Hai tham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 Fig. (1): O ptical transmi ttance of (ZnO )x(CdO)1-x films. The inse t shows Absorptance versus Wa velength Fi g. (2 ): Absorption coe fficient ve rsus Ph oton energy for (ZnO )x(C dO) 1-x thin film be fore an d afte r anne aling ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Hai tham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 Fi g. (3 ): O pti cal ban d gap Eg estimation for(ZnO )x(C dO) 1-x thin film befo re and after annealing Fig.(4): (n°)&(k°) versus Photon energy for (ZnO )x(CdO)1-x thin film before and after annealing ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Hai tham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 Fi g.(5): εr & εi versus Photon ene rgy fo r (ZnO)x(C dO) 1-x thin film befo re and after anneali ng. Fig. (6): S kin Depth versus Wavelength for (ZnO )x(CdO)1-x thin film before and after annealing ة مجلة إبن الھیثم للعلوم الصرفة و التطبیقی 2012 السنة 25 المجلد 1 العدد Ibn A l-Hai tham Journal f or Pure and Applied Science No. 1 Vol. 25 Year 2012 x(CdO)1-x(ZnO)تأثیرات المعاملة الحراریة في الخصائص البصریة ألغشیة المحضرة بطریقة التحلل الكیمیائي الحراري وداد هنو عباس قسم العلوم، كلیة التربیة األساسیة، الجامعة المستنصریة 2011 ایلول 20: قبل البحث في، 2011 نیسان 7:استلم البحث في الخالصة ، وعمـق االختـراق ،وثابت العزل الحقیقي والخیالي ،ومعامل االمتصاص ،درس تأثیر التلدین في النفاذیة البصریة المرسـبة علـى قواعـد زجاجیـة مـسخنة لدرجـة )x=0.05(الرقیقـة وبنـسبة x(CdO)1-x(ZnO)ألغـشیة وفجوة الطاقة البـصریة )C° 450 ( والمحـضرة بــسمك)nm 750 ( أظهــرت هــذه األغــشیة فجــوة طاقــة مباشــرة . بطریقــة التحلــل الكیمیــائي الحــراري قیمـة فجـوة الطاقـة البـصریة ازدادت مـن وكـذلك وجـد أن. ولمدة سـاعتین ) C°) 450 مسموحة متأثرة بالتلدین بدرجة حرارة )eV 2.50 ( قبــل التلــدین إلـى)eV 2.65 ( طیــف االمتــصاصیة والنفاذیـة فــي مــدى األطــوال ومــن تحلیـل ، بعــد التلــدین . كافة قد تغیرت بسبب التلدینان هذه المعلماتأظهرت النتائج ، (900nm-380)الموجیة عاملة الحراریةمتأثیر ال، الحراري التحلل الكیمیائي، الخواص البصریة، x(CdO)1-x(ZnO) غشیة أ:الكلمات المفتاحیة