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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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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