2010) 1( 23مجلة ابن الھیثم للعلوم الصرفة والتطبیقیة المجلد الخصائص البصریة والتركیبیة ألغشیة SnO2 المحضرة بطریقة الترذیذ صالح قدوري ھزاع قسم الفیزیاء ،كلیة التربیة ،الجامعة المستنصریة الخالصة ـــر ـــیة ت حضـ ـــذ الرقیقــــة وبســــمكین مختلفــــ SnO2أغشـ ـــى ســــطوح زجاجیــــة باســــتخدام طریقــــة الترذیــ ین علـ لمحضـره ذات ا لنمـاذجاوأظهرت النتـائج بـان . درس التركیب البلوري واتجاه األغشیة باستخدام طیف األشعة السینیة المغناطیسي ساويیوجد بأنه و حسب حجم الحبیبة . متعددة التبلور تركیب nm (25.35, 28.8) باسـتخدام لغشــاء ومكوناتـهلقیق لـددرس التركیــب السـطحي اSEM ألسـطح كلهــا اوكانـت EDX و بعــض الثوابــت البصـــریة مثــل معامـــل و )eV (3.85 كانــت مســـاویةفجــوة الطاقــة المباشـــرة و تحســـب. متجانســة ومرصوصــة -nm )300معامل الخمود والمركبة الحقیقیة والخیالیة لثابت العزل الكهربائي من خـالل طیـف النفاذیـة ضـمن المـدى ،االنكسار 900(. IBN AL- HAITHAM J. FO R PURE & APPL. SC I VO L.23 (1) 2010 Optical and Structural Prope rties of SnO2 Thin Films Prepare d by Sputte ring Method S. K. Haza’a Departme nt of Physics , College of Education, Al-Mustansiriyah Unive rsity Abstract SnO2 thin films of different two thicknesses were p repared an glass substrate by DC magnetron sp uttering. The cryst al st ructure and orientation of the films were invest igated by XRD p att erns. All the deposited films are polycryst alline. The grain size was calculated as 25.35, 28.8 nm. M orp hological and comp ositions of the films were p erformed by SEM and EDX analyses resp ectively. The films app eared comp act and rougher surface in nature. The allowed direct band gap was evaluated as 3.85 eV, and other op tical constants such as refractive index, extinction coefficient, real and imaginary p arts of dielectric constants were determined from transmittance sp ectrum in the wavelength range (300-900) nm and also analyzed. Introduction Transp arent conducting oxide thin films are of great interest, due to their variety of app lication. Consequently , thin films with high op tical transp arency and electrical conductivity have been a subject of invest igation since last century [1-3]. Thin oxide is one of the most p romising materials for op toelectronic and sensor app lications owing to its high transmittance and electrical conductivity . The SnO2 films are n-ty p e semiconductors with a direct op tical band gap of about (3.87-4.3) eV [4-5]. The structure of the material in its bulk form is tetragonal rutile with lattice parameters a=b=4.737 o A and c= 3.816 o A [6]. However in thin film form depending on the deposition technique its st ructure can be p olycryst alline or amorp hous [7]. The grain size is ty p ically (200-400) o A, which is highly dependant on deposition technique, temp erature, dop ing level etc. [4-5]. SnO2 films close to st oichiometric condition have low free carrier concentration and high resistivity , but non-st oichiometric SnO2 films have high carrier concentration, conductivity and transp arency. This comes about from an oxy gen vacancy in the st ructure so that the formula for the thin film material in SnO2-x, where x is the deviation from st oichiometry [4]. There are several dep osition techniques t o grow SnO2 thin films including chemical vapor depositions [8], magnetron sp uttering [9], sp ray p y rolysis [10] etc. In this work, we have invest igated the op tical p rop erties of SnO2 thin films p repared by sp uttering techniques. Experime ntal The SnO2 films were p repared by DC magnetron sp uttering. Fig.(1) is the schematic diagram of the equip ment. The glass substrate is p ositioned obliquely above the target. The substrate heater is p ositioned in the anode, and substrate temp erature is controlled by a thermocouple, and held constant at 200 o C. The substrate makes thermal contact with the anode through the cop p er subst rate holder, and the target anode dist ance is kep t at about 30mm. Tine oxide SnO2 was carried out by using magnetron sp utter source coupled to 60W dc p ower sup p lies. The vacuum was evacuated by an Edwards 306 p umping sy st em , the vacuum IBN AL- HAITHAM J. FO R PURE & APPL. SC I VO L.23 (1) 2010 chamber was exhausted by an oil-diffusion p ump at 2x10 -6 Torr in around 30 minutes, in an atmosp here of argon and oxy gen Ar 95% and O2 5% resp ectively, and magnetic field 370 gauss. Tin Oxide was sp uttered from targets on the glass substrate at temp erature 200 o C. The targets material are in the form of p lates with 60mm diameter and 2mm thickness and made from SnO2 p owder. The cryst al st ructure, surface morphology , and thickness of the films were analyzed by using x-ray diffraction (XRD) and scanning electron microscope (SEM ). The op tical transmittance measurements were p erformed with UV/VIS/NIR sp ectrop hotometer with a double beam in the wavelength range of (300-900) nm. Re sults and Discussion Fig. (2) Shows the diffraction patt erns of SnO2 thin films. As seen in this figure, the films are p olycryst alline, and characterized by the p resence of stronger but broader characteristic p eaks located at 2 = 26.6, 33.9, 37.8, 46.4, 51.7, 61.9, 65.4, arising out of reflection from (110), (101), (200), (210), (211), (310), and plan (301) resp ectively. The average grain size g can be estimated by using Scherreris formula. [11] G = 0.9 λ/ β cos (1) Where β is the full width at half maximum (FWHM ) of distinctive p eak (read),  the Braggs angle, and λ = 0.154 nm Cukα. The cry st allite size is estimated about 25.35, 28.8 nm for 0.802, 0.705 nm thickness resp ectively. The increase in films thickness enhances the p referred orientation with an increase in grain size and intensities The EDX sp ectra of the films are shown in Fig. (3), these sp ectra show that t he exp ected elements exist in the solid films. Fig.(4) shows scanning electron microscopy SEM of films at 20000X magnification. The films app eared to be compact and rougher surface in nature, the average grain size was measured between ( 200-250) nm To calculate the thickness of t he films, we used SEM p icture of the cross sections of the films as shown in fig. (5). The films t hickness was found to be 0.802 and 0.705 nm ap p roximately. For most app lications, high transmission in the visible range is very imp ortant. Fig. (6) Shows transmittance of SnO2 films. The average transmittance value of the films is >80 in the visible range, and it is evident that the transmittance decreases with the increase of thickness .T his is due to a decrease in light scatt ering losses. The absorpt ion coefficient α was calculated by using the following exp ression [12]  T t ln 1 a (2) Where T is transmittance, t is the films thickness. T he direct op tical band gap Eg was determined by using equation  2 1 gEhh  uua (3) IBN AL- HAITHAM J. FO R PURE & APPL. SC I VO L.23 (1) 2010 Where β is a const ant, Eg is determined by extrapolating the straight line portion of the sp ectrum to (αhυ) 2 =0. From this drawing, the optical energy gap, Eg = 3.85 eV is deduced and indep endent on the film thickness, as shown in Fig. (7). This value is very close to the p reviously reported data of SnO2 thin films ( 3-5). The complex op tical refractive index of the films is describ ed by the following relation [12] )()(  iknn  (4) Where n is t he real and k is the imaginary p art (extinction coefficient) of comp lex refractive ind ex. The refractive index and extinction coefficient of the films were determined from the followin g relations [12] 2 1 2 2 1 )1( 1 1 1 1                      k R R R R n (5)  a 4 K (6) Where R is t he reflectance. The n and k value decrease up to certain value with t he increasing wave length λ as shown in Fig. (8) and Fig. (9). This result is in a good agreement with earlier results [3،10] The dielectric constant ε is defined as [13] )()()( eee ir i (7) The real εr and imaginary p arts εi of dielectric const ant are related to t he n and k values, the εr and εi values were calculated by using the formulas [13] )()()( 22 e knr  (8) )()(2 e kni  (9) Both εr and εi values decrease with the increasing wavelength as shown in Fig.(10) and Fig.(11). It is clear that t he op tical constant has the same behavior, decreases up to certain value with the increasing wavelength and the effect of t hickness is only at log wave length. Conclusions The X-ray diffraction analysis showed that the SnO2 films are p olycryst alline in nature, and the increase, in film thickness enhances the preferred orientation with an increase in the grain size and intensities. Op tical measurements show that the film possesses high transmittance over 80% in the visible region and sharp absorp tion edge near 325 nm. The film has a direct band gap of 3.85 eV which is indep endent on the thickness. Op tical constants slitly depend on the film thickness. Re ferences 1.Penza, M .; Cozzi, S.; Tagliente, M .A.; M irenghi, L.; M artucci, C. and Quirini, A. (1999) thin solid Films., 71:349 2.Ishibashi, S.; Ota ,Y. and Nakamura, K. (1998), J. Vac. Sci Technol., A8 IBN AL- HAITHAM J. FO R PURE & APPL. SC I VO L.23 (1) 2010 3.Joseph, J.; M athew, V.; M athew, J.and Abraham, K.E., (2009), Turk. J. p hy s. , 33 4.Chop ra, K.L.; M ajor, S. and Pandya, D.k. (1983) thin solid Films, 102 5.Coutts, T.J.; Young, D.L., and Li ,X. (2000)M RS., Bull., 25:58. 6.Dawar, A.L. and Joshi, J.C., (1984) M ater J., Sci., 19: 91. 7.Bagh eri, M .M . - M ohagheri and M . Shokooh - Saremi, (2004), J. p hy s. D: App l. Phys., 37:1248. 8. Kojima, M .; Kato, H.; lmai ,A.and Yoshid a, A., (1988) J. App l. Phys. 64:1902 9.Stjerma, B. ; Olsson,E. and Granqrist C.G., (1994), J. App l. Phy s., 76:3797. 10.Shamala, K. S., Bull. (2001), M ater. Sci., 27 :295 11.Yang, X.C., (2002), M ater. Sci. Eng. B 93: 249 12.Gümüs, C.; Oz kendir, O. M .; Kavk H.and Ufuktepe, Y. (2006) Op toelectronics J. and advanced materials, 8:299. 13.Ilican, S.; Caglar, X.; C aglar, M .; Demirici, B. (2008), J. of Op toelectronics and advanced materials, 10:2592 Fi g. (1 ) :Schem ati c di agram of s pu tte rin g e quipmen t Fig. (2): X-ray spectra of S nO 2: a- 0.702 nm b- 0.805 nm thi ckness. DC-Diode Subst rate Anode SnO2 Target M agnet Cathode Bell-jar IBN AL- HAITHAM J. FO R PURE & APPL. SC I VO L.23 (1) 2010 Fig.(3): EDX spectra of S nO 2 Fig. (4): S EM image of S nO2 IBN AL- HAITHAM J. FO R PURE & APPL. SC I VO L.23 (1) 2010 Fig. (5): S EM picture of S nO2 thickness Fig. (6 ) Optica transmittance of SnO2 vs. wav e length. 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0 3 0 0 4 00 5 00 600 7 00 800 900 wavelength nm T % t=0.805 nm t=0.702 nm Fig.( 7 ) (ahu)2vs. photon en ergy. 0.0E+00 2.0E+10 4.0E+10 6.0E+10 8.0E+10 1.0E+11 1.2E+11 2.5 3 3.5 4 hu eV ( a h u )2 ( c m -1 e V )2 t=0.805 nm t=.0702 nm IBN AL- HAITHAM J. FO R PURE & APPL. SC I VO L.23 (1) 2010 Fig. ( 8) Re fractive index v s.wave length. 0 2 4 6 8 10 300 500 700 900 wavelength nm n t=0 .805 nm t=0 .702 nm Fi g. ( 9 ) extinction coefficie nt vs . wave length. 0 0.05 0.1 0.15 0.2 0.25 300 4 00 500 600 7 00 800 9 00 wavelen gth n m k t=0.805 nm t=0.702nm Fig.( 10 ) Real part of dielectric constant vs. wavel ength. 0 20 40 60 80 100 300 400 500 600 700 800 900 wavelength nm e r t=0.805 nm t=0.702 nm Fig.(11 ) Imaginary part of dielectric constant vs. wavele ngth. 0 0.5 1 1.5 2 300 500 700 900 wavelength nm e i t=0.805 nm t=0.702 nm