1994 Preparation and Properties of Sprayed

7/30/2019 1994 Preparation and Properties of Sprayed

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Thi n Soli d Fil ms, 248 (1994) 131- 139

Letter

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Preparation and properties of sprayedantimony trisulphide filmsC. H. Bhosale, M. D. Uplane, P. S. Patil andC. D. LockhandeDepartment of Physics, Shivaji U niv ersit y, Kol hapur-416 004, Indi a(Received January 17, 1994; acceped May 11, 1994)

AbstractSemiconducting Sb2S3 thin films have been prepared on glasssubstrates by spray pyrolysis. The films were deposited atoptimised conditions of substrate temperature and solutionconcentration and have been characterised for their struc-tural, optical and electrical properties. The films are semicon-ducting and amorphous. From the optical absorption study,the (indirect) bandgap is estimated to be 1.55 eV.

1. IntroductionRecently considerable attention has been given to the

preparation of thin metal chalcogenide films by varioustechniques [l-3]. Among various metal sulphides, anti-mony trisulphide finds some special applications in thetarget material for television cameras [4], microwavedevices [5], switching devices [6], and various optoelec-tronic devices [ 7-91. Savadago and Mandal [lo] andLockhande [ll] have deposited Sb2S, thin films bychemical bath deposition. Pawar et al. [ 121have preparedthe films using the solution gas interface technique, whileGeorge and Radhakrisshnan [91prepared them by a threetemperature method. Badachhape and Goswami [ 131obtained Sb2S3 films by vacuum evaporation.

Many bindary and ternary semiconductors on a varietyof substrates have been prepared by the spray pyrolysistechnique; the more important examples being CdS,CdSe, CdTe, CuInS,, CuInSe,, Bi,CdS, [ 141, CdSb,S[ 151, etc. However, no reports are available in theliterature on the preparation of Sb,S, thin films by spraypyrolysis. Merely spraying mixed solutions of antimonytrichloride and thiourea in an appropriate volume ontohot substrates does not form thin films of Sb,& on thesubstrates. Further, it it difficult to change the pH of thesolution from acidic to alkaline simply by adding NaOHor NH,OH solution.

We report here, for the first time, the deposition ofSb2S3 thin films by spray pyrolysis. Oxalic acid is addedas a complexing agent and thioacetamide is used as asulphide ion source. The deposited films have beencharacterised by X-ray diffraction (XRD) scanningelectron microscopy (SEM), optical and electrical mea-surements.

2. Experimental detailsThe films prepared by taking equimolar solutions of

antimony trichloride and thioacetamide in appropriatevolumes to obtain a Sb:S ratio of 2:3. Oxalic acid wasused as the complexing agent. 20 cm3 of 2 M oxalic acidwas mixed with 100 cm3 of 0.1 M antimony trichloride.This retards sulphide precipitate formation betweenantimony trichloride and thioacetamide. 150 cm3 of0.1 M thioacetamide solution was mixed with the com-pelxed antimony trichloride solution. The mixed solu-tion was immediately sprayed onto hot glass substrates(300 C). The spray rate was 14 cm3 min- and air wasused to atomise the solution.

The structural characterisation of the Sb,S, films wascarried out by analysing the X-ray diffraction patternobtained using a Philips X-ray diffractometer modelPW-1710 (1 = 1.5405 A for Cu Ka). The surface mor-phology was studied using SEM. The thickness of thefilms were determined by weight difference. Opticalabsorption spectra of the film were recorded by using aUV-VIS-NIR spectrophotometer model Hitachi-330(Japan). Resistivity was measured by a two probemethod in the temperature range 300-500 K.

3. Results and discussion

Spray pyrolysis is a simple and inexpensive methodfor preparing thin film semiconductors. The startingmaterials required to form the desired compound are inthe form of solutions which are sprayed onto preheatedsubstrates, resulting in the formation of thin films onthe substrates.

The direct mixing of antimony trichloride and thioac-etamide solutions results in a yellowish turbidity whichprohibits the spraying process. Oxalic acid forms astrong complex with antimony, and therefore the addi-tion of thioacetamide solution does not cause this tur-bidity. This mixed solution remains stable for about

Elsevier Science S.A.SSDI 0040-6090(94)09459-K


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10 min. When fine droplets of spray solution reach thehot substrates, owing to pyrolytic decomposition of thesolution, uniform, well adherent and dark grey coloredfilms of Sb,S, are formed on the substrates. Thepreparative parameters were optimised as substratetemperature 300 C and solution concentration 0.1 M.The film thickness was between 2 and 3 urn.

The X-ray diffraction pattern of the as-depositedSb,S, film is studied. The appearance of the broadX-ray spectrum suggests that the films are amorphous.A similar amorphous nature was reported for chemi-

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tally deposited Sb*S, film by Savadogo and Mandal[lo] and for vacuum evaporated films by Ghosh andVarma [ 161. SEM has been used for studying the sur-face morphology of the films. Figures l(a) - l(c) showSEM micrographs at three different magnifications. Themicrographs show voids and holes at relatively highermagnification. The film clearly demonstrates an unevensurface morphology devoid of any irregular crystallinegrowth. The optical absorption spectrum of the Sb,S3films is shown in Fig. 2. The optical absorption co-efficient a is of the order of lo4 cm-. The indirectbandgap was estimated by plotting (c&v) I* versus hv(Fig. 3). The extrapolation of the straight portion to the

(b)

Fig. 1. SEM micrographs of Sb,S, films at magnifications: (a) 100 x ,(b) 500x, (c) 3000x. Fig.

5.6 _

4.6

0I 3.4502Bk3m 2.24

1.0 I300 450 600 750 900

WAVELENGTH (nm )Fig. 2. Plot of optical absorption coefficient a versus wavelength 1.

0.0 1.5 3.0hu(eV 1

3. Plot of (ah~)~ versus hv.


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2. 5 12. 0 2. 2 2. 4 2.6 28 3. 0

( f 1x103

Fig. 4. Plot of log p versus l/T.

energy axis gives a bandgap of 1.55 eV. This valueagrees with values reported by other workers [ 10, Ill.The two probe method was used to measure the

electrical resistivity of the films in the temperaturerange 300-500 K. Figure 4 show the plot of log pversus l/T. The activation energy was estimated to be0.28 eV. The variation of resistivity with temperaturereveals that the films are semiconducting in nature.

4. ConclusionsThin films of Sb2S, have been deposited from an

oxalate bath using spray pyrolysis. The deposited

films are amorphous. The room temperature elec-trical resistivity was of the order of 10 Q cm. TheSb,S, was found to have an indirect bandgap ofEg = 1.55 eV.

References

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J. R. Lince, J. Mat. Res., 5(1990) 218.K. C. Mandal and 0. Savadogo, J. Mater. Chem., 1 (1991)301.C. D. Lockhande, Mat. Chem. Phys., 27 (1991) I.D. Cope, US Patent No. 2,875,359 (1959).J. Grigas, J. Meshkanskas and Orlimas, Phys. Stat. Solidi (A), 37(1976) 10.M. S. Ablowa, A. A. Andreev, T. T. Deb Akaev, B. T. Melekh, A.B. Peutsow, N. S. Sheridel and L. N. Shivilona, Sou. Phys.Semicond., 10 (1976) 629.M. J. Chokahngam, K. Nagarajo Rao, R. Rangarajan and C. V.Suryanarayana, J. Phys. D., 3 (1970) 1641.E. Montrimass and A. Pazera, Thin Solid Films, 34 (1976)65.J. George and M. K. Radhakrishnan, Solid State Commun., 33(1980) 987.0. Savadogo and K. C. Mandal, Sol. Energy Mater. Solar Cells,26(1992) 117.C. D. Lokhande, Ind. J. Pure Appl. Phys., 29 (1991) 300.S. H. Pawar, Shobha Tamhankar, P. N. Bhosale and M. D.Uplane, Ind. J. Pure Appl. Phys., 21 (1983) 665.S. B. Badachhape and Goswami, Ind. J. Pure Appl. Phys., 5( 1967) 477.R. Krishnakumar, V. Subramanian, Y. Ramprakash and A. S.Lakshimanan, Mat. Chem. Phys., I5 (1987) 385.S. H. Pawar, C. H. Bhosale and A. J. Pawar, Ind. J. Pure Appl.Phys., 26 (1988) 323.C. Ghosh and B. P. Varma, Solid State Commun., 31 (1979)683.

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1994 Preparation and Properties of Sprayed