ud

2

n a

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Received 3 February 2014; received in revised form 25 April 2014; accepted 29 April 2014

in the annealing of the structure in the presence of a source have been reported. The wet method consists in the immer-sion of the solar cell in a CdCl2 solution with a subsequentthermal annealing (Khaled et al., 2012; Chun et al., 2013);the dry methods are the annealing of the cell in a thermallygenerated CdCl2 vapor (Ferekides et al., 2004; Rios-Flores

Corresponding author. Tel.: +52 999 942 9400x2260.E-mail address: nhernandez@mda.cinvestav.mx

(E. Hernandez-Rodrguez).

Available online at www.sciencedirect.com

ScienceDirect

Solar Energy 107 (2014Keywords: CdS/CdTe chlorination; CdTe annealing; CHClF2; Grain boundaries; Chlorine incorporation

1. Introduction

The CdS/CdTe solar cells have achieved an eciency of19.6% in lab-scale and commercial modules with 16.1% e-ciency are available (http://www.rstsolar.com, 2013). Theactivation process of the CdS/CdTe structure before thedeposition of the back contact is the most critical step dur-ing the device fabrication in order to achieve high photo-conversion eciencies (Morales-Acevdo, 2006). It consists

of chlorine species. The main eect of the activation is topromote the recrystallization of the CdTe lm, whichresults in the grain growth, grain boundary passivation,doping of the CdTe and decrease in resistivity (Moutinhoet al., 1999; Ikhmayies and Ahmad-Bitar, 2012; Razykovet al., 2013); in the CdS/CdTe junction the lattice mismatchis reduced because of the interdiusion and the formationof the CdTexSlx/CdSyTely interface (McCandless et al.,1999; Xuanzhi, 2004). For activation, wet and dry methodsCommunicated by: Associate Editor Nicola Romeo

Abstract

The eect of annealing in CHClF2O2 gas mixture on morphological and chemical properties of CdTe thin lms deposited by con-ventional close space sublimation (CSS) has been investigated. Annealing was done at 400 C for 5 min in a mixture of CHClF2 and O2with partial pressures of 50 and 160 mbar, respectively, and to reach a total pressure of 800 mbar the annealing chamber was lled withAr. After annealing, residuals at the surface of lms were not removed in order to be study. High Resolution Scanning Electron Micros-copy (HR-SEM) and X-ray Photoelectron Spectroscopy (XPS) were employed for analysis. The annealing promotes the etching of theCdTe grains at faces and edges; as a consequence, the surface became smooth with a compact structure. The main improvement on mor-phology by the inclusion of O2 during the annealing was the reduction of the grain boundary width of lms. Chemical analysis of samplesannealed in CHClF2 with and without mixed oxygen showed that the oxygen in the gas mixture acts as a catalyst in the decomposition ofthe CHClF2. Annealing with the CHClF2O2 mixture reduces the oxidized compounds at the surface of lms and promotes incorpora-tion of Cl in the bulk. The experimental results give a clear demonstration why CdS/CdTe solar cells fabricated using CHClF2O2 duringchlorination treatments have better performance, as referred in a previous work. 2014 Elsevier Ltd. All rights reserved.Morphological and chemical stin CHClF2O

E. Hernandez-Rodrguez a,, V. RejoaApplied Physics Department, CINVESTAV-IP

bMaterials Science Laboratory, Faculty of Engineering, Uhttp://dx.doi.org/10.1016/j.solener.2014.04.032

0038-092X/ 2014 Elsevier Ltd. All rights reserved.y of CdTe thin lms annealedgas mixture

, I. Riech b, M. Acosta b, J.L. Pena a

Merida, C.P. 97310 Merida, Yucatan, Mexico

ersity of Yucatan, C.P. 97130 Merida, Yucatan, Mexico

www.elsevier.com/locate/solener

) 305313

Solet al., 2010) and the annealing in a gas mixture containingCHClF2 gas (Romeo et al., 2009; Rejon et al., 2013). Forindustrial application, the dry methods are more suitablebecause exposure to chlorine species and the annealingare made into one step, reducing the processing time. Also,the liquid waste obtained in the wet method is avoided.Romeo, has reported CdS/CdTe solar cells with eciencyclose to 16% by annealing the cells in the ArCHClF2gas mixture (Romeo et al., 2010); the CHClF2 is thermallydecomposed at 400 C and Cl in gaseous form is able toreact with the CdTe surface favoring its recrystallization.Recently, we have demonstrated that the annealing inCHClF2O2 gas mixtures improves the eciency of thesolar cells and therefore the solar cell parameters: open-circuit voltage (Voc), short-circuit current density (Jsc)and ll factor (FF) (Rejon et al., 2013), beyond the resultsobtained by annealing only in CHClF2 gas. In this work,we report our investigation on the morphological andchemical properties of CdTe thin lms annealed in ArCHClF2O2 gas mixture developed to understand the rolethat oxygen plays in the activation process which results inthe improvement of the CdS/CdTe solar cell eciency. Toevidence the inuence of each component in the ArCHClF2O2 gas mixture, three sets of samples we pre-pared. The rst one, used as a reference, was annealedusing just Ar; in the second and third set, the samples wereannealed by using ArCHClF2 and ArCHClF2O2 mix-tures, respectively.

On the other hand, the chlorouorocarbons are knownto be environmental pollutants and the destruction of theearth ozone layer has been associated to its diusion inthe stratosphere (Molina and Rowland, 1974). It has beenshowed that CHClF2, a chlorouorocarbon, can be decom-posed catalytically in the presence of a metal oxide andoxygen gas, with the selective formation of the CO, CO2,CHF3 and C2 byproducts (Li et al., 1996); these latest com-pounds being risk-free for the ozone layer.

Here, we show that the use of oxygen in the ArCHClF2O2 gas mixture improves the thermal decomposi-tion of the CHClF2 during the activation process. Then,our developed activation methodology not only enhancesthe solar cell eciency, but also it is suitable for technolog-ical application, because decomposition of CHClF2reduces the releasing of chlorinated compounds in gaseousform to the atmosphere, which are responsible for degrada-tion of the ozone layer.

2. Experimental procedure

The CdTe thin lms, with a thickness of 8 lm, weregrown on glass substrates by conventional CSS using tworectangular graphite blocks (10 10 0.5 cm), heated byhalogen lamps. The separation between graphite blockswas 35 mm and the atmosphere during the growth was0.1 mbar of O2 and 0.4 mbar of Ar. The source and sub-

306 E. Hernandez-Rodrguez et al. /strate temperature were 590 C and 550 C, respectively.The deposition rate of the CdTe lms was 1 lm/min. Afterthe CdTe thin lms were deposited, they were placed into aquartz ampoule within a total pressure of 800 mbar andwere annealed by using Ar (S1), ArCHClF2 (S2) andArCHClF2O2 (S3) gas mixtures. The partial pressuresused in the experiments for studying the CdTe thin lmsare shown in Table 1. The annealing was done at 400 Cfor 5 min. In order to study the chemical residuals at thesurface, the quartz ampoule was cooled down withoutremoving the gases after the annealing process. In thiswork, the setup of the annealing system is the same asthe one reported by Romeo (Romeo et al., 2010). Becausethe quartz ampoule is composed mainly by SiO2, it is akind of oxide that acts as a catalyst in the thermal decom-position of the CHClF2 in presence of O2 in the gas mix-ture, as can be seen in (Li et al., 1996). To study thechemical compounds formed during the annealing, theresiduals after activation were not removed from the CdTesurface. The HR-SEM, Backscattering Electron (BSE)imaging and chemical mapping were made by using aJEOL equipment model 7600F. The chemical bondingstate was investigated by XPS carried out in a ThermoScientic equipment model K-Alpha; XPS spectra wererecorded using a scanning step of 0.1 eV for high resolutionanalysis. Depth-proling was performed by sputtering thesamples during 15 s and after that, recording the XPS spec-tra; cycles were repeated until a cumulative sputtering timeof 285 s was achieved; spectra were calibrated by using theC1s emission at 284.6 eV. Atomic concentrations wereobtained by using standard sensitivity factors for ourXPS equipment.

3. Results and discussion

3.1. Morphological analysis

Fig. 1 shows the top view micrographs of as-grown andannealed samples. The as-grown sample is homogeneous,without cracks or pinholes; the grains are hexagonalshaped with size ranging from 2 to 7 lm, as can be seenin Fig. 1a. Samples S1 and S2 annealed in Ar and ArCHClF2, respectively, presented grains etched preferen-tially along the side faces, as can be observed in Figs. 1band c. However, the higher density of pores and the soften-ing of the grain edges showed by the micrograph in Fig. 1care evidence that etching is higher in S2 than in S1. Also, itcan be observed that new and small particles were formedin sample S2, which is attributed to the presence ofCHClF2 in the annealing atmosphere. In sample S3,annealed in ArCHClF2O2, etching of grains not onlyoccurred at the grain faces, but also at the grain edges, asshowed by the micrograph in Fig. 1d; in this sample, theformation of the new small particles was more evident thanin S2. Because of the annealing, the surface of sample S3became smooth with a compact structure, but as the mainfeature, the annealing made with CHClF2 mixed with O2

ar Energy 107 (2014) 305313originates the decrease of the grain boundary width. Bycomparison of the micrographs, it is quite evident the

enhancement of the morphologic characteristics in sampleannealed in the ArCHClF2O2 mixture (Fig. 1d) com-pared with sample annealed in the ArCHClF2 mixture(Fig. 1c). The details of the grains can be seen in the insetsof Fig. 1ad. In samples S1 and S2 etching was in form ofpores, but in sample S3 it was homogeneous around thegrains.

The formation of new particles at the CdTe surface afterthe annealing has been attributed to the thermal decompo-sition of the CHClF2 which promotes a recrystallizationprocess (Romeo et al., 2010). In our samples, micrographsshow that density of these small particles is higher insample S3 (Fig. 1d) than in sample S2 (Fig. 1c). Therefore,this is evidence that the presence of O2 in the gas mixtureduring the annealing enhances the CdTe recrystallization.

mixture enhances the recrystallization, improves the sur-face quality and decreases the grain boundary width ofthe CdTe decreasing the shunting probability.

3.2. Chemical analysis

The chemical analysis was performed by using XPS,BSE images and chemical mapping. The XPS analysiswas done both at the surface of the lms and in thedepth-proling mode, while BSE images and chemicalmappings were done at the surface.

3.2.1. Surface analysis

Fig. 2 shows the normalized Cd3d5/2 core level emissionof the as-grown, S1, S2 and S3 samples; it is possible toidentify one peak located at a binding energy of 404.9 eVin all spectra. This peak corresponds to the photoemissionassociated with CdTe bonds, according to the CdTe com-pound (Zapata-Navarro et al., 1994). However, the spectraof sample S3 has a shoulder at higher binding energies.Fig. 3 shows the detail of this spectrum; the experimentaldata was decomposed into two components with an energydierence of 0.9 eV; for these two components, the one

Table 1Partial pressure of the gases for the annealing process.

Sample CHClF2(mbar)

O2(mbar)

Ar(mbar)

Total pressure(mbar)

S1 0 0 800 800S2 50 0 750 800S3 50 160 590 800

E. Hernandez-Rodrguez et al. / Solar Energy 107 (2014) 305313 307In a previous work (Rejon et al., 2013), we have reportedthe photovoltaic characteristics of CdTe-based solar cellsactivated by using the same gas mixtures as used for theannealing of samples S1, S2 and S3; we have demonstratedthat the addition of O2 in the gas mixture enhances theelectrical characteristics and consequently the solar cellseciency. This better performance of the solar cells isexplained by our ndings here, because the O2 in the gasFig. 1. Top view SEM images of CdTe thin lms (a) as-grown, (b) Ar anlocated at the lower binding energy side corresponds tothe CdTe compound, while the other one at higher bindingenergy, 405.8 eV, is the Cd3d5/2 emission related to CdClbonds in the CdCl2 compound, in agreement with thereported in the literature (Niles et al., 1998).

In Fig. 4 the O1s core level emission of samples isshown. In the spectra, one peak can be identied at thebinding energy of 530.3 eV; it is correlated to the presencenealed, (c) ArCHClF2 annealed and (d) ArCHClF2O2 annealed.

SolFig. 2. Cd3d5/2 spectra of as-grown and annealed samples under dierentatmosphere conditions.

308 E. Hernandez-Rodrguez et al. /of native CdTe oxide at the surface of the lms (Niles et al.,1998). On the other hand, the shoulder at lower bindingenergy corresponds to water molecules adsorbed at the sur-face due to air exposure of samples (Azimirad et al., 2007).

The Te3d5/2 core level emission of samples is presentedin Fig. 5. In all spectra two peaks were identied at bindingenergies of 572.2 and 576.9 eV. The peak at 572.2 eV corre-sponds to an emission of the Te with valence 2, consistentwith the CdTe compound, as showed above by the Cd3d5/2emission. In the case of the peak at 576.9 eV, it correspondsto the emission of Te with valence +4, associated withTeO bonds (Zapata-Navarro et al., 1994; Khaled et al.,2012), which is according to the presence of oxygen showedby the O1s emission.

From the results described above, it is possible to ana-lyze the compounds present at the surface of samples.The Cd3d5/2 and Te3d5/2 emissions showed the presenceof CdTe in all samples as expected. Also, the Te3d5/2 andO1s emissions showed the presence of TeO bonds, whichare evidence of the presence of TeO2 compound and thenative CdTe oxide; the native CdTe oxide is composed

Fig. 3. Cd3d5/2 spectra of sample annealed under ArCHClF2O2atmosphere at 400 C.Fig. 4. O1s spectra of as-grown and annealed samples at 400 C underdierent atmosphere conditions.

ar Energy 107 (2014) 305313mainly by the CdTeO3 compound (Zapata-Navarroet al., 1994; Choi and Lucovsky, 1988) and from atomcounting it can be considered as CdTeO3 = CdO + TeO2(Niles et al., 1998), therefore, the signal from TeO bondsshowed by the Te3d5/2 core level emission comes fromTeO2 and native CdTe oxide, because in both compoundsthe valence of Te is +4. Comparing the intensity of this sig-nal for the as-grown and annealed samples, it can be seenthat annealing in the atmosphere with mixed oxygen (sam-ple S3) results in a substantial reduction of oxidized com-pounds at the surface.

In the case of samples S2 and S3 annealed in the atmo-spheres containing CHClF2 gas, the XPS showed the pres-ence of Cl, which demonstrates that the CHClF2 acts as aCl source at 400 C, however, the Cl concentration isgreater in S3 than in S2, as is showed by the elementalquantication presented in Table 2.

The oxygen mixed with CHClF2 plays an important rolefor incorporating more Cl in the CdTe lm. The higherconcentration of Cl in sample S3 explains the better etchingand recrystallization of the grains, as showed in the SEMimages in Fig. 1d. The O2 in the gas mixture improves

Fig. 5. Te3d5/2 emission of as-grown and annealed samples at 400 Cunder dierent atmosphere conditions.

Fig. 8e and f conrm its incorporation in samples S2 andS3, respectively; an important feature is that Cl mappingof S3 shows localized zones with high Cl content. TheseCl rich zones correspond with those which are Te decient,furthermore, its distribution match with the distribution ofthe new particles formed after the annealing. Therefore, itcan be concluded that these new particles are formed bythe CdCl2 compound.

Solthe thermal decomposition of the CHClF2 in the presenceof an oxide-catalyst, as is the case of the quartz ampoule(SiO2 mainly) in our activation system, by means of the fol-lowing chemical reactions:

CHClF2!O2 COHCl 2F

CHClF2!O2 CO2 HCl 2F

(

F CHClF2 ! CHF3 Cl

as has been reported (Li et al., 1996). In our experiment,the SiO2 from the quartz ampoule, the temperature andthe O2 in the gas atmosphere accelerate the CHClF2decomposition and the CO, CO2 and CHF3 compoundsare formed (Li et al., 1996). Therefore, the annealing underthe ArCHClF2O2 atmosphere delivers more Cl atomsavailable to react with the lm surface, resulting in a higheratomic concentration of Cl in sample S3 than in sample S2.More detail can be seen in Fig. 6; it shows the Cl2p spectraof samples S2 and S3 where the doublet Cl2p3/2 and Cl2p1/2is observed at binding energies of 198.5 and 199.9 eV,respectively; the binding energy position of this doubletcorresponds to a valence 1 of the Cl (Niles et al., 1998).It means that only compounds with the Cl having a valence1 can be formed. This fact conrms the presence of CdCl2in sample S3, as was analyzed from the Cd3d5/2 emission inFig. 3. In the case of sample S2, it was not possible toobserve any change in the shape of the Cd3d5/2 emissionas an evidence of the CdCl2 compound, however, it canbe due most likely because the lower concentration of Clin this sample, and therefore, a small amount of the CdCl2compound.

Another possibility for the Cl with a valence of 1 is theformation of tellurium oxychloride (Te6Cl2O11) which isassumed to be composed by the TeCl2O+5TeO2 molecules.An analysis of the oxidized part in the Te3d5/2 emission(Fig. 5) shows that for sample S2 the Te+4 signal increases

Table 2Surface atomic concentration of the as-grown and samples annealed underdierent gas mixtures.

Sample Te (%) Cd (%) O (%) Cl (%)

As-grown 25.5 31.7 42.8 S1 21.6 28.8 49.6 S2 18.9 24.9 47.1 9.1S3 22.7 33.3 20.7 23.3

E. Hernandez-Rodrguez et al. /with respect to the same signal in the as-grown and S1 sam-ples. This can be explained if the tellurium oxychloride ispresent in the sample because in TeO2 and TeCl2O thechemical valence of Te is +4, and therefore the Te3d5/2emission in both compounds is at the same binding energyposition. Then, incorporation of Cl in the lm promotesthe formation of the oxychloride that increases the Te+4signal.

Fig. 7 shows the BSE images of the samples; a contrastpicture is produced because the intensity of the backscat-tered electrons is strongly related to the atomic numberof atoms in the specimen, therefore, BSE images can showthe distribution of dierent chemical phases. Fig. 7a and bare the BSE images from the as-grown and S1 samples;they show a uniform chemical composition in the grainsalong of the analyzed area. The BSE image from sampleS2 (Fig. 7c) shows small dark points, and image of sampleS3 (Fig. 7d) shows dark clusters distributed along the sur-face and intermediate contrast zones along the grainboundaries, which indicates the presence of dierent chem-ical compounds. The analysis of SEM and BSE imagesshows that dierent chemical composition zones corre-spond to the particles formed after annealing.

The EDS elemental mappings showed that Cd and Te(images not presented for simplicity) are uniformly distrib-uted along the surface in the as-gown, S1 and S2 samples,but in S3, while Cd was uniformly distributed, there wereTe decient zones. Mappings in Fig. 8 show the O andCl distribution. As can be seen, O is along the grains inall samples (Fig. 8ad); however, a less brightness imagewas obtained for S3, which conrms the reduction of oxi-dized compounds. In the case of Cl, the mappings in

Fig. 6. Cl2p spectra of samples S2 and S3 corresponding to valence 1.

ar Energy 107 (2014) 305313 309Combining the XPS results, BSE images and the chem-ical distribution of Cd, Te, Cl and O in sample S3, thechemistry at the surface of the samples can be resumed asfollows: the grains in the as-grown sample and the sampleannealed in the Ar atmosphere (S1) are formed by CdTe,TeO2 and native CdTe oxide; these compounds are uni-formly distributed along the surface. In samples annealedin presence of CHClF2 (S2 and S3), the Cl is incorporated,and besides the CdTe, TeO2 and native CdTe oxide, CdCl2and Te oxychloride compounds are formed at the surface,however, in S3 where O2 was mixed in the annealing

Sol310 E. Hernandez-Rodrguez et al. /atmosphere a higher amount of Cl is in this sample. Thedark and bright zones in BSE images from samples S2and S3 indicated dierent chemical composition along thesurface of lms; because the dark zones in Fig. 8b are Tedecient and Cl rich as showed by the Fig. 8c, it is evidencethat CdCl2 is present at the lms. Distribution of thesedark and bright zones match with the distribution of thenew grains formed after the annealing of samples S2 and

Fig. 7. Backscattering electron image of sampl

Fig. 8. Oxygen mapping of (a) as-grown, (b) S1, (c) S2 and (dar Energy 107 (2014) 305313S3 as showed in SEM images (Fig. 1), therefore, thesenew grains are CdCl2. The grains are small and have lowerconcentration in sample S2 than in sample S3, it agreeswith the lower concentration of Cl showed by the XPSquantication for sample S2. The CdCl2 grains are distrib-uted along the grain boundaries, but they also form someclusters distributed over the lm surface. We can concludethat CHClF2 decomposes during the annealing and delivers

es: (a) as-grown, (b) S1, (c) S2 and (d) S3.

) S3 samples and Cl mapping of (e) S2 and (f) S3 samples.

Cl, which is incorporated in the lms and therefore recrys-tallization, grain etching and CdCl2 grains formation arepromoted.

It is important to remark that in our activation processthe O2 plays an important role for a higher decompositionof CHClF2, that makes it environmentally friendly, andtherefore suitable for industrial application because of the

main products obtained due to the decomposition ofCHClF2O2 at 400 C are CO, CO2 and CHF3 (Li et al.,1996).

3.2.2. Depth prole analysis

The evolution of the Cd3d5/2, Te3d5/2, O1s and Cl2pcore level emissions as function of the sputtering time is

E. Hernandez-Rodrguez et al. / Solar Energy 107 (2014) 305313 311Fig. 9. High resolution XPS scans of (a) Cd, (b) Te, (c) O and (d) Cl from samples S1, S2 and S3 as function of the sputtering time.

Solshown in Fig. 9. The Cd3d5/2 signal is constant in depth inall samples, as showed in Fig. 9a. The component of theTe3d5/2 signal at lower binding energies (2 valence)increases after the rst sputtering cycle and remains con-stant in the bulk of the lms, as can be seen in Fig. 9b;the increase in the signal is explained because sputteringremoves oxidized and/or chlorinated compounds fromthe surface, as has been described in Section 3.2.1, andexposes the CdTe. The component of the Te3d5/2 signalat higher binding energies (+4 valence) corroborates thisassumption; in Fig. 9b it can be seen that after sputteringthe intensity of this component decreases on samples S1and S2, which is according with the removal of oxidizedand chlorinated material; in the case of sample S3 its inten-sity is lower at the surface and does not change signicantlyafter sputtering.

The O1s core level emissions are presented in Fig. 9c; theintensity for samples S1 and S2 is higher in the surface, butafter sputtering, it decreases and then remains constant inthe bulk. On the other hand, for sample S3 the intensityis almost equal at the surface than in the bulk. The evolu-tion of the O1s emission is according with the evolution ofthe oxidized part of the Te3d5/2 emission and conrms thatthe formation of oxidized material in samples S1 and S2 ishigher than in sample S3. In the case of the Cl2p core levelemission, for sample S2, after few sputtering cycles, its sig-nal is nearly undetected, but in sample S3 it remains higherdepth in the lm; even after a sputtering time of 285 s, theCl signal is detected and seems to have reached a constantvalue. From the results described above, it can be con-cluded that oxygen added to form the ArCHClF2O2 mix-ture, is working not only for decomposition of CHClF2and to deliver more Cl, but also helps to incorporate Clin the CdTe bulk, as was demonstrated in S3. Moreover,a lower content of oxidized material was at the surface ofsample S3 than in samples annealed without mixing theO2. The improvement of the eciency and electrical char-acteristics of the CdTe solar cells reported in previous work(Rejon et al., 2013) by using the ArCHClF2O2 gasmixture during the annealing, can be explained by theincorporation of Cl in the bulk as showed here, becauseCl acts as a trigger of the recrystallization and passivatesthe grain boundaries of the CdTe thin lms (Moutinhoet al., 1999). Furthermore, the reduction of oxidized com-pounds at the surface under this activation methodologyimproves the CdTe surface for a good back contact basedon Cu/Mo (Rejon et al., 2013).

4. Conclusions

In summary, eects of thermal annealing under ArCHClF2O2 gas mixture on the morphological and chemi-cal properties of CdTe thin lms grown by the CSS processwere investigated. The as-grown CdTe thin lms were uni-form with a grain size of 27 lm. The grains of lms

312 E. Hernandez-Rodrguez et al. /annealed at 400 C in Ar and ArCHClF2 gas mixtureswere preferentially etched at the side faces. For sampleannealed in ArCHClF2O2 the main feature was thenarrowing of the grain boundaries, but this sample alsoshowed a smooth and compact surface with grainsuniformly etched at faces and edges. The CHClF2 wasthermally decomposed at 400 C; the O2 and quartzampoule acted as a catalyst on its decomposition, resultingin a higher content of Cl in the surface of sample annealedin ArCHClF2O2. The surface of as-grown and Arannealed samples were composed by CdTe, TeO2 andnative CdTe oxide, but annealing in the ArCHClF2 andArCHClF2O2 mixtures resulted in surfaces with CdTe,TeO2, native CdTe oxide, Te oxychloride and CdCl2 com-pounds. Annealing in the ArCHClF2O2 mixture resultedin the formation of CdCl2 grains distributed along thegrain boundaries and forming clusters in the lm surface.The inclusion of O2 gas in the annealing atmosphere pro-moted the incorporation of Cl in the bulk of the lm.

Acknowledgements

This work has been supported by CONACYT-Mexicounder contract CONACYT-SENER-SUSTENTABILI-DAD ENERGETICA (No. 207450), FORDECYT(No. 116157), FOMIX (No. 172298) and CeMIE-Sol PY-207450/25. Measurements were performed at LANNBIOCINVESTAV-Merida, under support from projectsFOMIX-Yucatan 2008-108160, CONACYT LAB-2009-01No. 123913 and CB2012/178947. E. Hernandez-Rodrguezacknowledges the nancial support of CONACY-Mexicofor the postdoctoral training at CINVESTAV-Merida(205760). The authors acknowledge O. Gomez, W. Cauich,D. Aguilar and D. Huerta for technical support andL. Pinelo for its secretarial assistance.

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Morphological and chemical study of CdTe thin films annealed in CHClF2O2 gas mixture1 Introduction2 Experimental procedure3 Results and discussion3.1 Morphological analysis3.2 Chemical analysis3.2.1 Surface analysis3.2.2 Depth profile analysis

4 ConclusionsAcknowledgementsReferences