Journal of Physics and Chemistry of Solids 73 (2012) 839–845

Contents lists available at SciVerse ScienceDirect

Journal of Physics and Chemistry of Solids

0022-36

doi:10.1

n Tel.:

E-m

journal homepage: www.elsevier.com/locate/jpcs

Factors affecting the electro-optical and structural characteristics of nanocrystalline Cu doped (Cd–Zn)S films

Ayush Khare n

Department of Physics, National Institute of Technology, G E Road, Raipur 492010 Chhattisgarh, India

a r t i c l e i n f o

Article history:

Received 25 August 2011

Received in revised form

19 November 2011

Accepted 14 February 2012Available online 3 March 2012

Keywords:

A. Nanostructures

C. X-ray diffraction

D. Optical properties

D. Luminescence

97/$ - see front matter & 2012 Elsevier Ltd. A

016/j.jpcs.2012.02.022

þ91 771 4052486; fax: þ91 771 2254600.

ail address: akhare.phy@nitrr.ac.in

a b s t r a c t

This work investigates the effects of the temperature, deposition time and annealing ambient on the

electro-optical and structural properties of nano crystalline (Cd–Zn)S films prepared by chemical bath

deposition (CBD). The deposited films being uniform and adherent to the glass substrates are

amorphous in nature and the crystallinity as well as the grain size is found to increase on post-

deposition annealing. The obtained specimens are thoroughly characterized before and after annealing

paying particular attention to their structure, composition and morphology. Annealing in air reduces

the extent of disorder in grain boundaries and energy band-gap. A correlation between the structural

and optical properties is investigated in detail. The surface morphology and structural properties of the

as-deposited and annealed (Cd–Zn)S thin films are studied using X-ray diffraction (XRD), scanning

electron microscope (SEM) and optical transmission spectra. The optical transmission spectra are

recorded within the range of 300–800 nm and 300–900 nm. The electroluminescent (EL) intensity is

found to be maximum at a particular temperature, which decreases with further increase in

temperature and peaks of photoluminescent (PL) and EL spectra are centered at 546 nm and 592 nm.

The emission intensity also increases with increasing thickness of the film.

& 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Optical, electronic, and structural properties of semiconduct-ing nano crystals have gained prominence due to their greatpotential in many applications ranging from DNA makers to lightemitting displays (LEDs) [1–3]. The success in converting theirproperties in technologically viable products lies in the ability tosynthesize highly pure, well characterized nano crystals andfabricating device structures based on them. In this context, nanosized semiconductors have attracted much attention in bothfundamental research as well as advanced technological applica-tions owing to their unique size dependent optical and electronicproperties. Furthermore, sulfide based phosphors such as ZnS andCdS (EgE3.7 eV and E2.5 eV, respectively) [3–6] have beenpotential candidates for their promising applications in electro-luminescent (EL), photoluminescent (PL) and photoconductive(PC) devices. Khare and Bhushan [7] reported some results of ELon (Zn–Cd)S:Cu, F films prepared by CBD technique whileBhushan and Pillai [8,9] discussed the results of PC and PL inchemically deposited (Cd–Zn)S:CdCl2, Ho films. The functionalproperties of these materials can suitably be tailored by varying

ll rights reserved.

the compositions of the Zn1�xCdxS ternary phase (0rxr1) [10],thus enabling the preparation of the phosphors with tunableemission wavelength and fluorescent screens.

Apart from the above, the size dependence of the band-gap isthe most identified aspect of quantum confinement in semicon-ductors. The band-gap increases as the particle size decreases[11]. In alloy nano crystals, the color-tuning emission propertiesare controlled by changing their constituent stoichiometry with-out changing the particle size [12–16]. Zhong et al. [13] and Vepet al. [14] found ternary alloyed nano crystals at high tempera-tures (250–330 1C). Other researchers opine that the compositionand internal structure are two important factors, which tune theoptical properties of phosphors [17].

Annealing has been used by many researchers as a tool toenhance the electro-optical characteristics and to study band-gapchanges in thin films [18,19]. Annealing is basically done to removeinstability followed by cooling so that the room temperature (RT)structure remains stable and strain free. It also assists in homo-genizing the structure and improving mechanical, physical, elec-trical and optical properties. Schottky type vacancies are commonin ionic-bonded semiconductors like ZnS and CdS. Hence postannealing has a major role in compensating such vacancies [20,21]and lowering the substrate temperature during deposition [22].

The properties of thin films prepared through different meth-ods are critically dependent on the nature of preparational

A. Khare / Journal of Physics and Chemistry of Solids 73 (2012) 839–845840

techniques. Among the various existing techniques of preparingthin films, chemical bath deposition (CBD) [23] is extremelyattractive because of its advantageous features over other thinfilm deposition techniques. It is relatively simple, cost effectiveand capable of depositing good quality, optically smooth, largearea, uniform and homogeneous films. The CBD process isperformed by slow release of S2� and controlled free Zn2þ andCd2þ ions in an aqueous solution. The use of CBD for preparingthin films is justified in the sense that the EL and PL cellsfabricated using these films are highly efficient and long lastingas discussed in detail later.

This paper reports and discusses the dependence of structuraland optical properties on deposition time, film thickness andtemperature. Simultaneously it explains elaborately the effects ofannealing on various characteristics of the film. The novelty ofpresent work lies in its being unique as far as dependence ofstructural and optical properties of (Cd0.7–Zn0.3)S films on anneal-ing is concerned.

2. Experimental details

2.1. Samples preparation

First of all a conducting layer, having resistivity E20 O cm islaid on glass substrate by spraying stannous oxide by spray-pyrolysis method [24,25] using stannous chloride (SnCl2 �2H2O)as the original chemical. The samples for EL studies are preparedthrough vertically dipping the cleaned substrates of highly trans-parent conducting glass plates (dimension¼75�24�2 mm3) in awater bath. The films are exposed at different temperatures fordifferent times on micro glass slide substrates, cleaned withdouble distilled water, acetone and ultrasonic cleaner. A 25 mlbeaker is used as a container for the reaction of chemicals. Thisbeaker is immersed in a water bath and heated to the desiredtemperature. The aqueous solution taken in the beaker containshighly pure and analytical reagent (AR) grade 1 M cadmiumacetate [Cd(CH3COO)2], zinc acetate [Zn(CH3COO)2], (zinc aceta-teþcadmium acetate¼7.00 ml), thiourea [SC(NH2)2], triethanola-mine (HOCH2CH2)3N (TEA) and 30% aqueous ammoniumhydroxide (NH4OH) (mixture’s pHE11). Thiourea and triethano-lamine are two commonly used sulphiding agents [26]. In thischemical reaction TEA acts as a complexing agent and pHbalancer. Appropriate amounts of 0.01 M solutions of copperacetate Cu [(CH3COO)3] (0.50 ml) and sodium fluoride (NaF)(2.00 ml) are also introduced in the original mixture beforeplacing the beaker into water bath. The beaker containing aqu-eous solution of the chemicals is covered with another invertedbigger beaker to prevent possible ammonia loss at highertemperature.

In above solution, F from NaF helps in the proper substitutionof Cu and thus the emission is due to Cu–F combination. Role ofNaF in photo conducting CdS powders prepared by firing at 500 1Cfor 1 h is found to be two fold [27,28] (i) it acts as a flux becauselanthanide impurities can not turn effective dopant in its absenceand, (ii) it acts as a dopant, since at its particular concentrationthe highest photo response is noticed in the system. If it acts asdopant in the present system, particularly F as co-activator helpsin the incorporation of Cu as activator. F from NaF also assists inthe compensation of charge.

In the beginning when precipitation starts, the solution isstirred for few minutes and no further stirring is done during thedeposition. The deposition is made in the static condition byplacing glass substrates inclined vertically to the walls of thebeaker until solution reaches a desired temperature. The tem-perature of bath is digitally controlled from outside with a timer.

After desired temperature is attained, the substrate is removedfrom the beaker and treated with distilled water to wash out theuneven overgrowth of grains at the surface and then dried bykeeping in open atmosphere under sun light until it completelydries. This helps in achieving longer operating life of EL and PLcell. The dried film is quite adherent to the substrate surface andis irremovable. Bhushan and Chandra [29] reported that chemi-cally deposited films have operating life of more than two years.The films are annealed at a temperature of 350 1C for 2 min in airusing a tubular furnace. Here, the subscripts to Cd and Znrepresent their percentage compositions in the solution.

The best annealing temperature from optical properties per-spective for CBD grown (Cd0.7–Zn0.3)S films in air is found to be350 1C above which the film starts deteriorating and film materialleaves the substrate surface. At higher temperatures glass platemay get deshaped due to which fabrication of EL cell turns difficult.

2.2. Measuring techniques

Optical transmission spectra are recorded with a Varian (UV–vis) DMS-100 spectrophotometer in 300–800 nm and 300–900 nm wavelength range. The various X-ray analyses are madeusing a computerized Philips diffractometer with Cu/K-alpharadiations. Further, SEM studies are performed with a LEO (430)scanning electron microscope. The EL and PL emission spectracollected with RCA-6217 photomultiplier tube (PMT) are recordedusing a Thermo-Jarrel Ash grating monochromator (Model-82415). The film thickness is measured through mass-differencemethod and is found to lay between 1 mm and 2 mm. In thismethod the sample is weighed before and after film deposition,then the thickness is calculated by distributing the difference ofmass on the film area.

2.3. Construction of EL cell

For EL studies, a thin layer of dielectric material (thickness�4 mm) is coated on the film using centrifuge (P8C LaboratoryCentrifuge) followed by an aluminum electrode sizing area 1 cm2,the last layer in fabrication and formed by coating it (thickness�100 A1) with 12// Hind Hivac vacuum coating unit (model-12A4D). The conducting glass plate and aluminum contact(area¼1 cm2) serve as the working electrodes for the device.

The EL cell discussed above is an example of metal–insulator–semiconductor (MIS) structure first proposed by Russ andKeneddy [30] where forward junction leads to recombination ofminority carriers in the sulfide layers leading to luminescence[31]. The reason for using aluminum as the electrode material isits high reflectivity, ability to prevent breakdown spread and goodadhesiveness to the insulating layer.

3. Results and discussion

3.1. Characterization studies

3.1.1. Scanning electron microscopy (SEM)

In order to determine the morphology and size of the grains,typical scanning electron microscopy measurements were car-ried. Fig. 1(a) and (b) display a typical SEM image of the (Cd0.7–Zn0.3)S films carried out at 10 k magnification, which revealsappreciable difference for as-deposited and annealed (in air)films. Non-uniformly distributed and nearly spherical grains areobserved in as-deposited sample; they are either single or in theform of clusters. In general, films are uniform across the substratesurface, but some vacant spaces still exist [Fig. 1(a)]. Afterannealing the distribution of grains turns more ordered and

Fig. 1. (a) SEM micrographs of unannealed (Cd0.7–Zn0.3)S film (magnification¼10 k). (b) SEM micrographs of annealed (Cd0.7–Zn0.3)S film (magnification¼10 k).

Fig. 2. (a) SEM micrographs of unannealed (Cd0.7–Zn0.3)S:NaF film (magnification¼10 k). (b) SEM micrographs of annealed (Cd0.7–Zn0.3)S:NaF film (magnification¼10 k).

A. Khare / Journal of Physics and Chemistry of Solids 73 (2012) 839–845 841

vacant spaces get occupied. This indicates the increase in crystal-linity of the films upon annealing. The diameter of grains inunannealed condition is found to lay around 180 nm, which afterthermal treatment becomes 200 nm. From this it is concludedthat grain size is larger after annealing, which may be due toelimination of point defects upon annealing, if there are less pointdefects, grains are to be bigger.

Fig. 2 presents the SEM micrographs of (Cd0.7–Zn0.3)S:NaFfilms in unannealed and annealed (in air) conditions(magnification¼10 k). In as-deposited sample, grains are seen inthe form of nano fibers along with a flower shaped cluster, whichupon annealing get combined and exhibit cabbage like structure.This is not the overall appearance of the film at high magnifica-tion but just an interesting feature of the film surface. In thesemicrographs the average fiber diameter is found to range between40 nm and 50 nm. This calculation is based upon Heyn’s interceptmethod [32] in which the total number of grains falling over astraight line are counted and using magnification value, averagegrain size is estimated. Addition of NaF to the original mixtureleads to more and more adhesion of grains, which grows in acabbage type structure. After annealing the cabbage shapedcluster of grains turns into flower shaped structure and nowentire sample is occupied by particles.

3.1.2. X-ray diffraction (XRD)

The crystalline phases of nano particles are identified by X-raydiffraction. Fig. 3 presents the comparison of the XRD patterns of

(Cd0.7–Zn0.3)S nano crystal alloy before and after annealing. Boththese diffractograms exhibit cubic phases with prominent diffrac-tion peaks of ZnS and CdS indexed as (111)c, (220)c and (311)c

planes. The assignment of diffraction lines is made by comparingwith JCPDS files of ZnS (cubic, JCPDS 05-0566) and CdS (cubic,JCPDS 10-454) and the evaluated and reported values of para-meters like lattice interval, lattice constant and Miller indices. Inannealed diffractogram, no new peak is observed and it isconcluded that irrespective of thermal treatment all the resultingfilms are nano structured. This feature suggests that nano crystal-line dimensions are almost unaffected by annealing inducedgrowth processes and are primarily influenced by the adoptedCBD conditions.

The average grain size (g.s.) of the nano crystalline film isestimated using Debye–Scherrer’s formula [33,34]

g:s:¼ Kl=bcosy ð1Þ

where l is the wavelength of X-ray radiatios, b the full width athalf maxima (FWHM) of the peak, K a constant and y is theBragg’s angle. The observed peaks are quite broad in both thecases, which again is an indicative [35] of nano sized particles. Forannealed case, resulting films are nano structured with averagegrain size �200 nm. The crystallite sizes are found to increaseupon annealing. Here it is important to mention that the cabbageis a chunk of homogenously nucleated precipitate that settles onto the real film that is underneath cabbage. The XRD datacorresponding to two cases are summarized in Table 1. Generally,in CBD technique, the average particle size of the precipitate is

Fig. 3. X-ray diffractograms of unannealed (upper) and annealed (lower) (Cd0.7–Zn0.3)S film.

Table 1Observed and reported XRD data of (Cd0.7–Zn0.3)S films.

System Latticeinterval (A1)

Millerindices(hkl)

Intensity ofdiffractedX-rays

Latticeconstant (A1)

Obs.

values

Rep.

values

Obs.

values

Rep.

values

Obs.

values

Rep.

values

(Cd0.7–Zn0.3)S

unannealed

3.34 3.36 (111)c-CdS 100 100 5.78 5.82

2.04 2.06 (220)c-CdS 40 80 5.79 5.82

1.89 1.91 (220)c-ZnS 36 51 5.39 5.41

1.64 1.63 (311)c-ZnS 29 30 5.18 5.41

(Cd0.7–Zn0.3)S

annealed

3.34 3.36 (111)c-CdS 100 100 5.76 5.82

2.03 2.06 (220)c-CdS 37 80 5.74 5.82

1.88 1.91 (220)c-ZnS 28 51 5.88 5.41

1.62 1.63 (311)c-ZnS 31 30 5.33 5.41

Fig. 4. Plots of film thickness with deposition time as a function of deposition

temperature.

A. Khare / Journal of Physics and Chemistry of Solids 73 (2012) 839–845842

much larger than the average grain size of the polycrystalline film[36,37].

3.2. Effect of deposition time, film thickness and growth temperature

on the optical properties

The variation in film thickness with deposition temperature atdifferent deposition times is shown in Fig. 4. From the figure, it is

evident that at lower temperatures the film thickness varieslinearly with deposition time, i.e. at lower temperatures rate ofdeposition is constant whereas at higher temperatures the filmthickness varies faster followed by saturation. If the thickness ofvarious samples at a particular deposition time are compared, it isobserved that lesser is the time of deposition, more is the film

Film Thickness (nm)800

Em

issi

on I

nten

sity

96

98

100

102

104

106

108

110

112

114

116

1000 1200 1400 1600 1800 2000 2200

Fig. 5. Variation of emission intensity with film thickness.

1.05

1.1

1.15

1.2

1.25

1.3

1.35

0Temperature (°C)

Film

Thi

ckne

ss (µ

m)

20 40 60 80 100

Fig. 6. Film thickness variations with bath temperature (Deposition time¼70 min).

Fig. 7. Variation of EL brightness with temperature for (Cd0.7–Zn0.3)S: Cu,

NaF film.

A. Khare / Journal of Physics and Chemistry of Solids 73 (2012) 839–845 843

thickness. This can be understood on the basis that at lowertemperatures, particles face less resistance and are more mobileresulting in lesser adhesion of these films to the substrate [38].

Fig. 5 presents the variation of emission intensity with filmthickness. It is noticed that as the film gets thicker, the intensity ofthe near band-edge emission increases. This is explained on the basisthat with increasing thickness, more and more material on the film isnow available for the excitation. This enhancement in intensity mayalso be due to decrease in auto-doped defect concentration andimprovement in crystalline quality of the films [39,40].

Various temperatures from 40 1C to 80 1C in steps of 10 1C havebeen used in the co-depositing (Cd0.7–Zn0.3)S film to obtain theoptimum temperature. Fig. 6 shows an increase in film thickness asthe temperature increases from 40 1C to 70 1C followed by decreasetill 80 1C. The rise in the film thickness is due to the increase in thehydrolysis of SC(NH2)2 as the temperature increases [41], providingthe S2� necessary for the metal chalcogenide formation. Thereaction rate and kinetic energy also increase at higher tempera-tures, bringing about increased interaction and subsequent deposi-tion at volume nucleation centers of the substrate [42]. Theobserved decrease in film thickness at temperatures above 70 1Cis due to the decrease in ammonia concentration because at hightemperatures, the rate of evaporation is high. Although the beakercontaining aqueous solution is properly covered, yet completeprevention of ammonia loss is not manageable.

3.3. Temperature dependence of optical properties

The temperature dependence of EL brightness for (Cd0.7–Zn0.3)S: Cu, NaF film is shown in Fig. 7. It is observed that withincreasing temperature, EL brightness increases nearly linearly,becomes maximum at a particular temperature (of sample) of40 1C followed by decrease at further higher temperatures. It islearnt that a maximum emission takes place at around 40 1Ctemperature. From this observation, it is clear that traps areinvolved in this process, which after release of electrons at atemperature close to 40 1C, give rise to free carrier generationresulting in the maximum emission [43]. The increase in ELbrightness is attributed mainly to the increased carriers in thequantum wells for radiative recombination. Also, due to a betterspatial overlap of electrons and holes in the quantum wells, theincreased number of carriers can be more efficiently recombinedin the nano rod device. Higher EL implies more radiative recom-binations and is an indicative of less defects, imperfections,impurities etc. [44]. The results are analyzed with the tempera-ture dependence of electron tunneling rate from discrete level toband following the phonon assisted tunneling theory [45]. Thedecrease in EL brightness at higher temperatures occurs due tothe temperature quenching effect of thermally induced dissocia-tion of the exciton and the exciton–phonon interaction [46]. Inthis condition the electrons move back to the ground statewithout emitting any photon.

It is earlier reported [47] that the EL intensity increases withthe applied voltage and frequency. At low frequencies theincrease in EL intensity is fast, which tends towards saturationat higher frequencies. These results suggest that the nano phos-phors based ac EL devices are better suited for the low voltageapplications. According to acceleration–collision mechanism theelectrons liberated from donors or traps by the action of field areaccelerated sufficiently to produce collisions with the electrons inthe activator centers, which ionize or excite the activator centers.The emission takes place in the later part of the AC cycle when itis reversing.

3.4. Effect of annealing on the optical properties

The annealing is carried out at the temperature of 350 1C for2 min in air and then samples are allowed to cool to room

Fig. 8. PL emission spectra of (Cd0.7–Zn0.3)S film in unannealed (______) and

annealed (———————) conditions.

0

200

400

600

800

1000

1200

0

Unannealed

Annealed

Wavelength (nm)

EL

Inte

nsity

(Arb

. Uni

ts)

200 400 600 800

Fig. 9. EL spectra of (Cd0.7–Zn0.3)S film.

Fig. 10. Optical transmission spectra of (Cd0.7–Zn0.3)S film in unannealed (______)

and annealed (———————) conditions.

A. Khare / Journal of Physics and Chemistry of Solids 73 (2012) 839–845844

temperature naturally. The PL spectra of unannealed andannealed (Cd0.7–Zn0.3)S:Cu, NaF film in the wavelength rangefrom 350 nm to 500 nm are presented in Fig. 8. The emission peakis centered at 425 nm, which shifts to 414 nm after annealing.This can be understood on the basis that upon annealing, there isenhanced proper substitution of impurities resulting in improvedemission intensity [48]. This results due to change in band-gapand increase in grain sizes of the polycrystalline film. This isattributed to the band to band transition of the host. Thisobservation is supported by SEM studies also where in annealedcase, grain distribution is more ordered and defect free. Theenhancement in the emission is due to the fact that high band-gap ZnS shell material suppresses the tunneling of the chargecarriers from the CdS nano fibers to the surface atoms of the shellresulting into more photo-generated electrons and holes confinedinside the CdS cores. Consequently, passivated non-radiativerecombination sites that exist on the core surfaces lead toenhanced PL efficiency [49]. This can also be understood on thebasis of SEM micrographs where in annealed case empty spacenow gets occupied leading to more excitation.

Fig. 9 shows the distribution of EL intensity for as-depositedand annealed (Cd0.7–Zn0.3)S:Cu, NaF samples. They almost matchwith the corresponding PL spectra. Apparently, the emissionprocesses are the same for both PL and EL. The investigated EL

films exhibited blue emission and a brightness of 90 cd/m2 undersinusoidal excitation. It is earlier observed and reported [47] thatdue to increase in concentration of Cu, the emission peak changes,which indicates that Cu is mainly responsible for the emission[50]. The electroluminescence spectrum ranges from about 300–700 nm and there is peak at 439 nm for as-deposited sample,which gets blue-shifted to 421 nm in case of annealed film. This isbecause upon annealing more and more Cuþ2 may substituteCd2þ/Zn2þ , either in the substitutional or interstitial positions. Itshould be noted that the ionic radii of Znþ2, Cdþ2 and Cuþ2 are0.74 A1, 0.97 A1 and 0.72 A1, respectively. Cu ions also play therole of a sensitizer and form acceptor levels whose energy levelsare anomalously deep (beyond 2.7 eV above the top of valenceband) and located near the bottom of conduction band [51];hence shift towards lower wavelength side compared to theband-gap is expected. The substitution of Cu is facilitated inpresence of the anion like F (NaF). Thus, the emission is correlatedto presence of Cu, F combination. Also, Cu can assist in theformation of conducting layer for realizing the excitation of thematerials with the field.

The optical transmission spectrum is an important tool to studycomposite films. It is considered to analyze the optical character-istics and constants of the film material. Fig. 10 shows the opticaltransmission spectra recorded for (Cd0.7–Zn0.3)S film in unannealedand annealed conditions. The film is quite transparent with theaverage transmittance reaching values up to 60%, over 800 nm inannealed case. It is noted that after annealing the film becomesmore transparent to incident light. This is probably due to refillingand homogenizing of the structure upon annealing [52]. Theimprovement in transmittance is also attributed to the enhance-ment in the crystallinity and decrease in surface roughness. Theoptical transmittance of a film is known to strongly depend on itssurface morphology. The increase in transmittance upon annealingis associated to an increase in the grain-size as can be seen in theSEM images. As the grain size increases, grain boundary scatteringis reduced, so that the transmittance is improved.

Fig. 11 shows the optical transmission spectra of (Cd0.7–Zn0.3)Sfilms at different growth times. It is evident from the figure that thetransmission intensity decreases with increasing deposition time.With increase in deposition time a red-shift is also noticed in thespectra, which proves that the rate of Cd2þ integrated into CdZnSsystem is faster than the rate of Zn2þ during the growth of CdZnSfilm. The band-gap values of the as-deposited thin films vary from2.5 eV to 2.42 eV before and after annealing. These values arecalculated from Tauc’s plots using corresponding absorption spectra,

Fig. 11. Optical transmission spectra of (Cd0.7–Zn0.3)S film at different

deposition times.

A. Khare / Journal of Physics and Chemistry of Solids 73 (2012) 839–845 845

which are considered to be complementary of transmission spectra.The absorption coefficient (a) and the band-gap Eg are related by thefollowing expression in direct band gap materials [53]

a¼Cðhv�EgÞ

1=2

hvð2Þ

where Eg is the optical band-gap and C the speed of light. Thedecreased band-gap of the films after annealing is due to theimproved crystalline nature of the material [54].

4. Conclusions

The CBD technique is a simple and suitable method forobtaining smooth, uniform, high reflecting and strong adherentCdZnS thin films. Annealing of the films leads to homogenizingand ordering of distributed grains. SEM studies exhibit non-uniform distribution of grains, which after thermal treatmentturn ordered. XRD results reveal cubic phases along with promi-nent lines of ZnS and CdS. The average grain-size, estimated fromthese studies, lies in the nano range. The variation in filmthickness with deposition time is linear at lower temperaturesand attains saturation at higher temperatures while for a parti-cular deposition time; film thickness is maximum at a particulartemperature and decreases at higher temperatures. Temperaturedependence of EL brightness shows a maximum at 40 1C followedby decrease due to temperature quenching. Annealing of filmsalso results in greater PL intensity with peak shifting towardslower wavelength side indicating increase in grain-size of thepolycrystalline film. Comparison of EL intensity distribution foras-deposited and annealed sample shows blue shift in wave-length. Transmission spectra of these films show improvement intransparency upon annealing, which is due to smoothening of thefilm surface. Thus, it is inferred that CBD is a simple and viabletechnique for film deposition and the corresponding parametersare strongly affected by the factors like annealing, temperatureand deposition time.

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