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Gamnn Railiation Effect on the Inter-Band Transitionsof SnO2Thin Films
N. F. Htbubi, T. H, Abood, A. H. Dagir
At-fuIustonsiriya University -College of Education
ABSTRACTSnOz thin films have been prepared by chemical spray pyrolysis
technique. The absorption and transmission spectra has been
checked for the dePosited films before and after irradiation b)'
Gamma-rays in order to determine the influerce of the absorbed
dose on the absorptance, absorption coefficient aod the forbiddenererry gap in all kinds of transitions. It has been shorvn that / -rlys
affected these parameters by decr€asing the absorptance, the
absorption coeflicient and increased the value of the energr gap forall kinds of transitions.
idril(,-+!,J+-. ,qJrJ-.i s,.l-++sil ++.,.:t rq,rl drr:'J+ iiii SnOr
'*'iil '')'-
}.U ij-*. J..l ur,i!iJ ul ,.,.!l.i gJ! r,.i # il,j;y Jl5l reiuj,IJ ir..L.!fl
C+ ,rl.1;-t*.1 ijll'I tJ+i ro.L-.:..)l &! .l+alr:''Jl .rb L':"J1 :tJ+ll
eL.l&J:t . l--.i.Yl ,'. tr. Or !' J-.lJrI .f. sb oJil tru iJ (,l 5.J il .,iYui,'yl
.€Jt&)l 'sts
s! iJJB'j! iiG! ;J+! Lri 'r.ll rjlJ o'1":'!l
INTRODUCTION
Thin films of tin Oride (SnO2), that are coming under the category
of transparent and conducting oxides (tCOs) haYe attracted the
researches because of their wide applications in both industry and
resesrch [11. This oxide are used Ior a varietY of applicatiorsincluding architectural windows, flat-panel display' thin Iilmphotovoltaic, smart window and polymer based electronics' Among
ihe available (TCOs), SnOz thin films on glass substrate are used
ertensirely on ghss windows for en€r$/ consert'rtion and as
electrodes in thin films [2-5].Generally SnCIr is used as a precursor for Sn and limited work had
been reported using SnCll instead of SnC[ [61. Since usrge of SnC.ll
is more economical compared to Snclr, it is worthwbile
investigating the proPerties of pure SnOl thin film prepared from
the former, using a new preparrtion cotrditions for the first time in
Iraq.The aim of this erperimental work is to investigrte the changes in
some optical Properties of SnO2 thin films under the influence ofGamma-ra1s.
Experimental Dettils
Thin nlms of SoO: were prepared by homemade spray pyrolysis
setup from SnCl: prec[rsor. The details on the experimental s€tup
can be found elservhere [?1. An llg of SnCl:.2H:O dissolved in
concentnted HCI by heating at 90 'C for l0 minutes and
subsequently diluted with ethanol formed the starting solution' The
films were preprred rvith the oPtimizcd substrrte temPerature of
650 K. The overall amount of solutioD in erch case was prepared up
to 100 ml aod the same amount of solutiotr was spraycd on pre-
heated glass substrates. The r€Peatcd srperiments for this
deposition showed that lilms could be reproduced easily' Aneriensive care wts taken in giving sulficient sPray inten'al behveen
successire sprays for the substrate get back to deposition
temperature tfter uodergoing thermal dccomposition'The transmittrnce and absorPtioo spectra were obtlined using
Pye-Unicom Double beam spectrophotometer in the waYelength
range (200-900) nm.Theie lilms were exposed to T'rays resulc from Co-60 with activity
38 pci for t$'o inten'als of absorbed dosc each interval rvas for one
rveek and for each inlen'rl the tralsmittrnce and absorbance rvere
recorded,
Results and Discussion
The absorption sPectra for the lilm dePosited at 650 K are shown in
figu re (t). it can be clearly seen that the lbsorptance was reduced as
the exposure dose increased.The same behaviour rlas seen in ligure (2) for the absorption
coelficient (a ) lvhich was calcuhted from the relation [8]:
ヤ
a = 2.303::....... (l)d'
where A is the absorbance, d is the thickness of the lilm.The type of optical trrnsition, $hether direct or indirect cln be
determined by studying the dependence of a on the photon ener$''(iv) for direct/indirect oPtical transition betreen parabolic band.The relation between the absorption coeflicient and photon enerryis given by: [91(ahv)= 111r, - 9, t g,,)' ..... (2)
where A is essertitlly a constlnt, Ep is the Phonon energr and E, isthe cnerry gap. ln direcl transition (Ee=0) n is equrl to 0.5 and 1.5
for allowed and forbidden trlnsition resPectiYely' For indir€cttrrnsition n=2 for atlowed transition and 3 for forbidden transition.The optical band gaps of these lilms such as the direct allowed and
forbidden transition and indirect brnd gap for the allorved
trrnsition were determined from a plot ol (ahv)'1,(qhv)t'1 '(ahv)"
t
versus photon energy resPectively. These yield struight lines with rninterc€pt on the ,varis. Since there is no evidence for the eristenceof indirect forbidden transition.These transitions were shown in figures (3-5) and table (l)represents the value for etch case, we see that the enerry glpincreased as the absorbed dose increased. That was due to highenergr radiation, such as 1-ra1's chrnge the Ph!'sical Prop€rties ofthe material they peoetrate. Tbe chrnges are strorgly dependent on
the internal structure of the absorbed substrrces. It is believed thrtionizing radiation c!uses structurll defects (called color centers ororygen vacancies in orides) leading to their density change on theerposure to y-rays [01.
Conclusions
l- The preparing conditions used in this work were successfullyenhanced the deposited thin films. They were be more adherent and
highly free from pinhole in comparison with other preparingconditions.2- y-ra]'s affected all the parsmeters ulder int'estigation and thislerds us to conclude that 1-rr!'r decreased the degree of cr,vstlllinity'
Samples
Direct allowed
transition (ohr)r
(ev)
Direct Forbidden
transition
(αh171"(eD
Indireci allowed
transition (crhr,)la
(eD
Unirritation 255130
090
irritation(one
week)
irritation (two
weeks)178
Table(1)
References
1- A. L. Dawar, J. C. Joshi, J. N1at. Sci.' 19' 1(198"1).
2- P. S. Patil, l\Iatter Chem. Phys., 59, f85 O999).
3- J. L. Vosser, Phys. Thin Films' 9' l(1977).
4- E. Elangovan, II. P. Singh' M.S. Dharmaprkash, K'
Ramamurthi, J. of Optoelctronics and Advanced ldaterials, 6' 197
(2004).
5- T. W. Kim, D. V. Lee, D' C. Choo, Ir1. Jung, V. S. Yoon, J. of
Applied Physics,90, lll (2001).
6- B. Thangaraju, Thin Solid Films, 402'71(2002).
7- O. P. Agnihotri, NI. T. Mohamed, A. K. Abass, K, L. Arshak'
Solid State Commum., 47, 195 (1983).
8- N. F. Habubi, A. A. Yousif, S. S. Chaid' J. of College of
Education, 4, l(200{).
9- D. Pathinettam Padit'an, A. Illarikani, K. R. IlIurali, Crlst. Res'
Technol., 35, 9-19 (2000).
l0- K. Arshak, O' KorosR'nska, Sensors' 2' 3'17(2002).
r Before initation
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O After irritation (one week)
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Figure (l): Shorvs absorptance againstphoton energy beforethe unirritation and after irritation (for one \\'eek, and two weeks)
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Figure (2): Shorvs absorption coefficient against photon energy beforethe uninitation and after irritation (for one u'eek, and trvo rveeks)
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Figure (3): t"r,o' "g"in.tlilt;;;-t ror the samples underinYestigation
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