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Structural, electrical and optical properties of radio frequency sputteredindium tin oxide thin films modified by annealing in silicon oiland vacuum

Ram Narayan Chauhan a, R.S. Anand b, Jitendra Kumar a,⁎a Materials Science Programme, Indian Institute of Technology Kanpur, Kanpur 208016, Indiab Department of Electrical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India

a b s t r a c ta r t i c l e i n f o

Article history:Received 22 December 2012Received in revised form 30 January 2014Accepted 5 February 2014Available online 15 February 2014

Keywords:Thin filmsR.F. sputteringElectrical propertyOptical transmittanceElectron paramagnetic resonance

Indium tin oxide thin films (thickness ~300 nm) have been deposited on glass at the substrate temperature of65 °C by radio frequencymagnetron sputteringwith the power density of 1.25W cm−2 under argon atmosphereand annealed subsequently in silicon oil at 200° and 350 °C to investigate systematically the effects on their struc-tural, optical and electrical properties. As-deposited thin films after annealing at 350 °C exhibit marked changesin the microstructure with emergence of crystallites (average size ~51 nm), high optical transmittance(~86%) in the visible range, and electrical resistivity as low as 1.24 × 10−3 Ω-cm with high figure of meritof 5.35 × 10−3 Ω−1 square — indicating their suitability as transparent conducting anode for opto-electronic devices. Further, the above findings are compared with those observed in case of films annealedin vacuum (~4 × 10−4 Pa) at 350 °C.

© 2014 Elsevier B.V. All rights reserved.

1. Introduction

The deposition of indium tin oxide (ITO) thin films on glass at lowsubstrate temperatures (b100 °C) yields thin films that are comprisedof small crystallites. Hence, light absorption no doubt increases due toenlargement of grain boundaries but conductivity decreases too be-cause of enhanced trapping of charge carriers. As a result, polymersolar cell fabricated with ITO film anode displays high short circuit cur-rent density with limited open circuit voltage and low fill factor [1].There is a need therefore to develop suitable transparent conductingelectrodes for improved device performance. The conduction in ITOthin films depends largely on grain growth and oxygen vacancies [2].It can possibly be increased by proper selection of film depositionmeth-od and subsequent treatment processes. The ITO thin films prepared bydifferent techniques, viz., sputtering (d.c./radio frequency), evaporation,chemical vapor deposition, sol–gel, and spray pyrolysis, display dissim-ilar characteristics [3,4]. Among these, radio frequency sputtering issimple, safe and produces dense uniform films at low substrate temper-ature over a large areawith high deposition rates [5]. Such ITOfilms dis-play low resistivity (10−3–10−4 Ω-cm) and high transparency (N80%).Nevertheless, their properties can still be improved further by post-de-position heat treatment process, e.g., decrease of resistivity by annealing

in vacuum [6]. This requires a vacuum furnacewhich is costly and cum-bersome. A cheap and simple process which involves annealing in sili-con oil is therefore suggested here to obtain high quality ITO thinfilms. This paper essentially deals with their preparation by radio fre-quency (r.f.) sputtering to study the effect of annealing in silicon oil onthe film microstructure and opto-electronic properties. In addition,films have been annealed in vacuum (4× 10−4 Pa) at 350 °C formakingcomparison of the characteristics with those annealed in silicon oil.

2. Experimental details

Indium tin oxide (ITO) thin films of thickness ~300 nm have beendeposited on glass substrates by r.f. sputtering using In2O3:SnO2

(90:10 wt.%) target of 99.99% purity. The glass substrate was RCAcleaned, dried in air andmounted inside the sputtering chamber at a dis-tance of 12 cm from the target. The chamber was evacuated to a basepressure of 1 × 10−4 Pa prior to (i) heating the glass substrate at100 °C for the removal of the moisture and (ii) film deposition at a rateof 1.2 Å s−1 by sputtering in argon gas plasma using 1.25 W cm−2 r.f.power density. During film deposition, the argon gas pressure in thechamber was maintained at 0.10 Pa. The substrate was initially held at55 °C but reached ~65 °C during the course of deposition. The filmswere annealed in silicon oil at 200° and 350 °C each for 1 h 30min. In ad-dition, ITOfilmswere annealed in vacuum (~4×10−4 Pa) at 350 °C for 1h 30 min for comparative studies. The phase, morphology, optical trans-mittance and sheet resistance of ITO films were investigated with a

Thin Solid Films 556 (2014) 253–259

⁎ Corresponding author. Tel.: +91 512 2597107.E-mail addresses: [email protected] (R.N. Chauhan), [email protected]

(R.S. Anand), [email protected] (J. Kumar).

http://dx.doi.org/10.1016/j.tsf.2014.02.0230040-6090/© 2014 Elsevier B.V. All rights reserved.

Contents lists available at ScienceDirect

Thin Solid Films

j ourna l homepage: www.e lsev ie r .com/ locate / ts f


Thermo Electron ARL X'TRA X-ray diffractometer with copper, CuKα1

radiation (wavelength λ= 1.54056 Å), Carl Zeiss SUPRA 40 VP scanningelectronmicroscope (operated at 10 kV in SEmode), an Ocean optic fiberspectrometer model USB 2000, and a four-point resistivity probe, respec-tively. The film thickness was measured by a Dektak 6M Stylus profiler.Also, Hall measurements were made for the determination of the carrierconcentration (n) and the mobility (μ) [7]. The photoluminescence (PL)was recorded with a fluorescence spectrometer (Edinburgh instrumentsFLSP 920) to identify the defects present in films. The electron paramag-netic resonance spectra of films were obtained using a Bruker electronspin resonance spectrometer to detect singly ionized paramagneticand doubly ionized diamagnetic oxygen vacancies with a modulationfrequency of 100 kHz at amplitude of 0.5 mT and a sweep width of800 mT [8]. A Horiba model Jobin YUON HR800 UV Raman spectrometerwas used to record the Raman spectra with an excitation wavelength of632.7 nm to check various vibration modes present.

3. Results and discussion

3.1. Impact of annealing in silicon oil

3.1.1. Structure and morphologyThe XRD patterns of ITO thin films are shown in Fig. 1. As-deposited

films exhibit poor crystallinity. The films annealed in silicon oil at 200°and 350 °C show diffraction patterns corresponding to a body centeredcubic phase similar to In2O3 (a = 10.110 Å, Z = 16, space group Ia

–3;

JCPDS file # 88-2160) and display no evidence of individual tin or itsoxides. This suggests the incorporation of tin in In2O3. However, thelattice parameter of as-deposited ITO film is slightly larger (10.212 Å).This enlargement is possibly caused by the presence of stress and tinin ITO films [9]. Shigesato et al. [10] have also reported increase in latticeparameter for ITO powder and attributed that to the presence of Sn4+ inIn2O3. After annealing the ITO films at 200° and 350 °C, the lattice pa-rameter decreases to 10.134 Å and 10.126 Å, respectively due to stressrelief. Kumar and Mansingh have observed (222) preferred orientationin In2O3 films when the substrate was held in thermalized region [11].The preferred orientation (222) or (400) occurs depending upon theprocessing conditions, e.g., at moderate pressure (0.7 Pa) adatomsmove actively upon arrival on the substrate and yield (400) orientedgrains. On the other hand, (222) preferred orientation results whenadatoms have low density or restricted movement due to insufficientenergy [12,13]. In the present case, the film is deposited at low argongas pressure (0.1 Pa) and hence corresponds to poor adatoms' densityhaving little interaction, resulting in (222) preferred orientation. Thepeak intensity ratio (I222/I400) which defines texturing increases from1.45 to 2.24 after annealing the films in oil at 200 °C but rises up to2.12 only at 350 °C. The deviation in texturing of films with annealingtemperature may be associated with improved crystallinity and graingrowth [14]. The average crystallite size (D) has been found usingScherrer formula (D = 0.9 λ / β cosθ, where λ is X-ray wavelength, βis corrected full width at half maximum, θ is the Bragg angle) [15]. Thevalues of D as deduced from diffraction data of 222 peak are 44 and51 nm for films annealed in silicon oil at 200° and 350 °C, respectively.As-deposited films show poor crystallinity because the crystallizationtemperature of ITO is 150 °C and prolonged bombardment of ions thatoccur at a low argon pressure (0.1 Pa) raises the substrate temperatureto 65 °C only [16,17]. The morphology of ITO films shown in Fig. 2 re-veals granular structure with grain growth after annealing in siliconoil at 350 °C. On the contrary, vacuum annealing process inhibits thegrain growth somehow and yields smaller grains (Fig. 2d).

3.1.2. Raman studiesRaman spectra of ITO films deposited by r.f. sputtering as such and

after annealing in silicon oil at 200° and 350 °C each for 1 h 30 minare presented in Fig. 3 alongwith the respective Gaussiandeconvolutioncurves (continuous, gray color). Indium oxide (In2O3) belongs to

bixbyite-type body centered cubic structure (a = 10.110 Å, Z = 16with space group Ia

–3) and contains two types of cations: 8 In3+ ions

at ‘b’ sites with–3 symmetry and 24 In3+ at ‘d’ sites with 2-fold point

symmetry. Also, 48 oxygen ions occupy ‘e’ sites with no symmetry. Forsuch a structure, six possible vibrational modes predicted are [18]

4Ag 4Eg 14Tg 5Au 5Eu 16Tu

Fig. 1. XRD patterns of r.f. sputtered ITO thin films: (a) as-deposited (b, c) after annealingin silicon oil at 200° and 350 °C, and (d) after vacuum annealing at 350 °C.

254 R.N. Chauhan et al. / Thin Solid Films 556 (2014) 253–259


where Ag, Eg, and Tg symmetry vibrations are Raman active but IRinactive modes. On the other hand, Tu vibration modes are IR activebut Raman inactive. The remaining Au and Eu vibrations are inactive(IR and Raman both). Thus, the total Raman activemodes can be twentytwo only. The active modes observed in In2O3 so far by different groupscorrespond to Raman shifts 109, 135, 144, 175, 240, 248, 307, 325, 329,366, 433, 471, 476, 495, 504, 517, 584, 630, 637 and 707 cm−1 [18–21].The ITO films exhibit Raman shifts as 109, 135, 307, 366, 495, 517, and630 cm−1 of host In2O3 itself [20]. Also, Sn–O links give rise to aRaman shift of 633 cm−1 [20]. As-deposited ITO films depict a strongbut broad asymmetric signal at 555 cm−1 with a poor peak around210 cm−1 (Fig. 3a). The Gaussian deconvolution fit (continuous, graycolor) reveals five Raman shifts at ~210, 407, 476, 555, and 631 cm−1

(Fig. 3a). While the peak at 210 cm−1 is attributed to Sn–O [22], the re-maining signals may arise from In2O3:Sn or In2O3. After annealing filmsat 200° and 350 °C, peak at ~210 cm−1 disappears whereas a new oneemerges at ~322 cm−1 (Fig. 3b and c) due to non-stoichiometry orIn2O3 itself [23,24].

3.1.3. Electrical propertiesThe electrical parameters, viz., sheet resistance (Rsh), electrical resis-

tivity, (ρ) and mobility (μ) of ITO thin films are given in Table 1. Theelectrical resistivity has been deduced from ρ = (Rsh t) using thesheet resistance (Rsh) data and film thickness (t = 300 nm). Noticethat the sheet resistance and electrical resistivity decrease significantlyby annealing the films at 200° and 350 °C in silicon oil, e.g., the valuesbecomeRsh=41.4 Ω/square and ρ=1.24×10−3Ω-cmafter annealingat 350 °C for 1 h 30 min. The electron concentration (n) values deter-mined from Hall measurements in ITO films annealed at 200° and350 °C are 5.43 × 1020 and 6.09 × 1020 cm−3, respectively. Their mobil-ity (μ) data obtained using ρ values and the relation ρ= 1/neμ (where nis carrier concentration and e is electronic charge) correspond to 7.5,and 8.3 cm2/V-s, respectively [25]. Notice that these figures are lowerthan ~42 cm2/V-s of bulk ITO [26]. The mobility is limited by scatteringof charge carriers due to phonons, grain boundaries and electron/ionized impurities [27]. The phonon scattering is expected to be insig-nificant here as measurements are made at the room temperature.The grain boundary scattering becomes appreciable with small crystal-lites/grains. Also, grain boundaries act as sink for species and charge

carriers. As a consequence, a potential barrier (ϕ) is developed thereand causes hindrance in carriermovement. The barrier (ϕ) is proportion-al to (w− f D)2, where w is barrier width determined by the number ofdisorder atom layers, D is the grain size, and f is a fraction in the range 1/15–1/50 [1]. Obviously, ϕ increases with decrease in ‘D’ and in turn re-sponsible for lowering the mobility. The scattering from ionized impuri-ties becomes effective if their density is high and comparable to theelectron concentration. In this situation, electrons themselves interacttoo and retard mobility [28]. Since the electron concentration of ITOfilms is significant and lies in the range (2.47–6.09) × 1020 cm−3 withgrain size marginally different (44 and 51 nm), electron–electron/impu-rity scattering mechanism seems to be largely limiting the mobility [29].The high carrier concentration is related to oxygen deficiency and tindoping in In2O3. Each oxygen vacancy acts as an ionized donor and con-tributes one or two electrons. Also, Sn4+ substitutes In3+ and creates adonor level near the conduction band comprises of indium 5 s or 5 p[30]. These processes can be described as [31]

Oo→Vþþo þ 2 eþ 1

2O2 gð Þ↑ ð1aÞ

Oo→Vþo þ eþ 1

2O2 gð Þ↑ ð1bÞ

Oo→Vo þ12O2 gð Þ↑ ð1cÞ

2 SnO2→2 SnþIn þ 3 Oo þ 2 eþ 1

2O2 gð Þ↑: ð2Þ

The grain growth may also release trapped electrons and raise thecarrier concentration further.

3.1.4. Optical propertiesThe optical transmittance spectra of ITOfilms shown in Fig. 4a reveal

significant increase in transmittance (80–92%) in the visible region afterannealing in silicon oil at 200° and 350 °C. The absorption coefficient

100 nm

(d)

(a) (b)

(c)

Fig. 2. Scanning electron micrographs of r.f. sputtered thin films: (a) as-deposited (b, c) after annealing in silicon oil at 200° and 350 °C, and (d) after vacuum annealing at 350 °C.

255R.N. Chauhan et al. / Thin Solid Films 556 (2014) 253–259


(α) is deduced from transmittance (T) data in the transition zone (usingα=t−1 ln (1 / T), where t is the film thickness) and plottedwith its de-rivative [dα / d(hν)] as a function hν (Fig. 4b). Notice the shift in the ab-sorption edge towards a lower wavelength (or higher energy) in thecase of films annealed at a higher temperature. This clearly indicateswidening of the band gap [24]. With increase in carrier density, twocompetitive processes occur simultaneously, viz., i) partialfilling of con-duction band causing widening of band gap (ΔEBM) or Burstein–Mossshift and (ii) band gap narrowing (ΔEBGN) or shifts of bands towardseach other due to electron–electron and electron–impurity scattering[32]. According to Hamberg and Granqvist [33], the absorption edgecan be assumed at the point of maximum derivative in the (α) versus

hν plot. The corresponding energy can be therefore taken as the mea-sured optical band gap (Egop), such that

Eopg ¼ Ego þ ΔEBM−ΔEBGN ð3Þ

with Ego being the intrinsic direct band gap of In2O3 (3.55 eV). The aboveexercise gives Egop value for as-deposited ITO films as 3.80 eV. The Egop in-creases to 3.97 and 4.01 eV after annealingfilms in silicon oil at 200° and350 °C, respectively (Fig. 4b). Burstein–Moss shift (ΔEBM) is expressedas [34,35]

ΔEBM ¼ π2 h2

2 m�e

3 nπ

� �2=3ð4Þ

where h is Planck's constant, n is the carrier concentration, and me⁎

(=0.31mo for ITO; mo is themass of free electron). OnceΔEBM is calcu-lated for a given ‘n’ from Eq. (4),ΔEBGN can be deduced from Eq. (3) tak-ing Ego = 3.55 eV. The values of Egop, n, ΔEBM and ΔEBGN are listed inTable 1 for all ITO thin films. The band gap narrowing (ΔEBGN) is givenby [36]

ΔEBGN ¼ A n1=3 1− nc=nð Þ1=3h i

ð5Þ

where nc is the critical carrier density for onset of bandgapnarrowing andA is the fitting parameter. The intercept at abscissa and slope of ΔEBGN vsn1/3 plot give nc and A as 2.34 × 1019 cm−3 and 6.72 × 10−8 eV cm, re-spectively (Fig. 5a). Incidentally, the experimental data lie on the ΔEBGNvs n plot (Fig. 5b), produced using Eq. (5) with A and nc given above.

The energy gap (Egop) of the film is related to its linear refractiveindex (no) and expressed as [37]

ffiffiffiffiffiffiffi5Eopg

s¼ n2

0 þ 26

: ð6Þ

The values of refractive index (no) of as-deposited and annealed ITOthin films fall in the range 2.17–2.21 (Table 1). These figures are close tothe refractive index 2.1 of ITO films reported by Yang et al. [38]. The de-crease in refractive index of films annealed at a higher temperature isassociated with increase of Egop due to rise in the carrier concentration[39].

Thefigure ofmerit (FTC) of a transparent conductor is defined by [40]

FTC ¼ T10 Rshð Þ−1 ð7Þ

where Rsh is the sheet resistance and T is the fractional transmittance ata particularwavelength (λ). So, films exhibiting high transmittance andlow sheet resistance correspond to high figure of merit. Thus, ITO filmsannealed at 350 °C in silicon oil with transmittance of 86% at 500 nmcorrespond to figure of merit of 5.35 × 10−3 Ω−1 square (Table 1).This value is larger than 1.20 × 10−3 and 2.15 × 10−3 Ω−1 square butcomparable to 5.50 × 10−3 Ω−1 square reported for ITO films grownby spray pyrolysis [41–43].

3.1.5. PL and EPR studiesPL spectra of ITO films recorded with excitation wavelength of

298 nm are shown in Fig. 6. As-deposited films exhibit broad and asym-metric PL spectrum extended from UV to green region. The Gaussian fit(continuous, gray color) depicts four symmetric peaks (Fig. 6a) centeredat 398 nm (3.12 eV), 437 nm (2.84 eV), 467 nm (2.66 eV), and 548 nm(2.26 eV). The peak at 398 nm is assigned to near band edge transitionwherein electrons in the defect level near the conduction band recom-binewith holes at a level near the valence band through a radiative pro-cess [44]. By annealing the films in silicon at 200° and 350 °C, emissionintensity of near band edge transition increases due to improved crys-tallinity (Fig. 6). The emission peaks centered at 437 nm (2.84 eV),467 nm (2.66 eV), and 548 nm (2.26 eV) originate from the various

Fig. 3. Raman spectra with Gaussian fitting curves of r.f. sputtered ITO thin films: (a) as-deposited and (b, c) after annealing in silicon oil at (b) 200° and (c) 350 °C.



oxygen vacancies (Vo, Vo+, Vo

++), respectively [45–49]. Evidence for thepresence of singly ionized paramagnetic oxygen vacancies (Vo

+) comesof EPR data (described below).

Annealing of films in silicon oil causes

• shift of the near band emission towards lower wavelength (386 and380 nm) with enhanced intensity (Fig. 6b and c).

• no change in emission peak positions of 437, 467 and 548 nm.Markedimprovement in blue emission at 437 nm (Fig. 6b and c).

The emissions at 2.84, 2.66, and2.26 eV canbe attributed to transitionsVo+ → Valence band, Vo

+ → (VIn − Vo) hole and Vo++ → (VIn − Vo) hole,

respectively. With the increase of the annealing temperature more oxy-gen vacancies are formed and this leads to the increase in the intensityof emission peaks. This fact is more prominent in films annealed at350 °C (Fig. 6c). The creation of anion vacancies involves adsorption of sil-icon species by ITO film and subsequent reaction with oxygen to form avolatile SiOx compound. The oxygen vacancies in ITO may be neutral(Vo), singly ionized (paramagnetic Vo

+) and doubly ionized (diamagneticVo++ species) [47]. Electron paramagnetic resonance (EPR) spectra of ITO

Table 1Structural, electrical and optical parameters of r.f. sputtered 300 nm thick ITO films as-deposited and after annealing in silicon oil or vacuum for 1 h 30 min at specified temper-atures.

Parameters As deposited Annealing atmosphere

Silicon oil Vacuum

200 °C 350 °C 350 °C

2θ (degree) 30.281 30.518 30.547 30.589Crystallite size, D (nm) 44 44 51 43Lattice parameter, (a) (Å) 10.212 10.134 10.126 10.111Carrier concentration, n (1020 cm−3) 2.79 5.43 6.09 6.40Sheet resistance, Rsh (Ω/square) 82.36 51.31 41.35 40.26Resistivity, ρ (10−3 Ω-cm) 2.47 1.54 1.24 1.21Mobility, μ (cm2/V-s) 9.10 7.50 8.30 8.10Optical band gap, Egop (eV) 3.80 3.97 4.01 4.02Burstein–Moss shift (ΔEBM) (meV) 500 780 840 864Band gap narrowing (ΔEBGN) (meV) 250 360 380 394Refractive index, no 2.21 2.18 2.17 2.17Transmittance value for wavelength500 nm (T%)

70 83 86 86

Figure of merit, FTC (10−3 Ω−1square) 0.343 3.02 5.35 5.50

Tra

nsm

itta

nce

(T%

)dα

/ d(

hv)

Wavelength (nm)

hv (eV)

(a)

(b)

Fig. 4. (a) Optical transmittance spectra of ITO thin films, and (b) showing the correspond-ing {dα / d(hν)} versus hν plots.

n1/3 (106 cm−1)

(a)

ΔE B

GN

(meV

)ΔE

BG

N (m

eV)

n (1021 cm-3)

(b)

Fig. 5. (a)ΔEBGN versus n1/3 plot of ITO thinfilms, and (b) showingΔEBGN versus n plot fol-lowing ΔEBGN = A n1/3 {1− (nc / n)1/3} [36]; the experimental data are also presented.



films shown in Fig. 7 exhibit peaks at 331.6mT and correspond to g-factorof 2.03 against 2.0023 of free electrons [21]. This result provides evidencefor the existence of singly ionized paramagnetic oxygen vacancies (Vo

+)in ITO films. PL emission peaks at lower wavelengths, i.e., 365 nm(3.397 eV), 380 nm (3.263 eV), and 386 nm (3.212 eV) are possibly

originating due to the reduced (of course, to different extent) nature ofITO films in line with the reports of rutile TiO2 − x system [49–51].

3.2. Impact of vacuum annealing

Thediffraction pattern of the r.f. sputtered ITO thinfilms after vacuumannealing at 350 °C is similar to that observed after heating in silicon oilat 200 °C in terms of (222) preferred orientation and average grain size~43 nm, but, with a slightly lower lattice parameter 10.111 Å. Obviously,grain growth is poor in vacuum annealed ITO films (Fig. 2c and d). Theelectrical parameters are given in Table 1. The values of electrical resistivity(ρ), electron concentration (n), and mobility (μ) are 1.21 × 10−3 Ω-cm,6.40 × 1020 cm−3 and 8.10 cm2/V-s, respectively; the lower electricalresistivity is due to high electron density resulting through the creationof anion vacancies via oxygen desorption during the vacuum annealingat 350 °C. The films exhibit optical transmittance of ~86% in the visibleregion and the optical band gap (Egop) of 4.02 eV (Fig. 4b).

In summary, post-deposition annealing in silicon oil at 350 °C im-proves the crystallinity, optical transmittance and electrical propertiesof r.f. sputtered ITO thin films so that they become suitable for photovol-taic applications. The focus of the study has been to demonstrate a costeffective and distinct heat treatment process in replace of an expensiveand cumbersome vacuum annealing technique used currently. Notethat the r.f. sputtered ITO thin films upon annealing in silicon oil at350 °C exhibit electrical and optical properties similar to those achievedafter vacuum treatment (Table 1) and with better grain growth. Duringannealing at 350 °C, silicon species penetrate into the pores of ITO filmsand undergo an exothermic reaction with oxygen to form volatile SiOx

compounds (e.g., enthalpy of SiO2 = −910.70 kJ mol−1) [52]. The

Fig. 6. Photoluminescence spectrawith Gaussian fitting curves in thewavelength range of340–575 nm for ITO thin films: (a) as-deposited (b, c) after annealing in silicon oil at 200°and 350 °C, and (d) after vacuum annealing at 350 °C.

Fig. 7. (a) EPR absorption spectra and (b) derivative of absorption as a function ofmagnet-ic field for ITO thin films as-deposited and after annealing in silicon oil at each 200° and350 °C for 1 h 30 min.



large amount of heat evolved in the process raises the local temperatureand facilitates grain growth.

4. Conclusions

ITO thin films (thickness ~300 nm) deposited by radio frequencysputtering on glass with 1.25 W cm−2 power density at substrate tem-perature of ~65 °C can be annealed effectively in silicon oil at 350 °C toimprove their characteristics (optical transmittance ~86%, and electricalresistivity ~1.2 × 10−3 Ω-cm) to become suitable for photovoltaicapplications.

Acknowledgments

Thanks are due toDepartment of Science andTechnology, NewDelhifor providing thefinancial support andDr. Sri Sivakumar, Department ofChemical Engineering, IIT Kanpur for extending the Photoluminescencemeasurements facility.

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