Journal of Crystal Growth 394 (2014) 39–48 Contents lists available at ScienceDirect Journal of Crystal Growth journal homepage: www.elsevier.com/locate/jcrysgro Deposition of binary, ternary and quaternary metal selenide thin films from diisopropyldiselenophosphinato-metal precursors Sumera Mahboob a,b, Sajid N Malik a,c, Nazre Haider d, C Q Nguyen e, Mohammad A Malik a, Paul O’Brien a,n a Schools of Chemistry and Materials, The University of Manchester, Oxford Road, Manchester M13 9PL, UK Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan c School of Chemical & Materials Engineering, National University of Sciences and Technology, Islamabad 44000, Pakistan d National Engineering and Scientific Commission, Islamabad 44000, Pakistan e Faculty of Chemistry, University of Science, Vietnam National University, Hochiminh City, Vietnam b art ic l e i nf o a b s t r a c t Article history: Received October 2013 Received in revised form 20 January 2014 Accepted 23 January 2014 Communicated by R Fornari Available online 11 February 2014 The tetragonal chalcopyrite phases CuInSe2, CuGaSe2 and CuIn0.7Ga0.3Se2 have been deposited onto the glass substates by Aerosol Assisted Chemical Vapour Deposition (AACVD) from a mixture of [Mx(iPr2PSe2)y] complexes (M¼ In, Ga, Cu) at temperatures between 300 1C and 500 1C The thin films were characterized by powder X-ray diffraction (p-XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) The bulk compositional properties have been studied by energy dispersive X-ray (EDX) analysis SEM and AFM studies demonstrate a significant variation in morphology of the deposited materials at different deposition temperatures & 2014 Elsevier B.V All rights reserved Keywords: A1 Thin films B1 Chalcopyrite CIS AACVD CIGS Introduction Metal chalcogenide semiconductor thin films have attracted significant research attention during the past few decades because of their exciting photoelectrical characteristics Copper selenide, a member of II–VI family of semiconductors, has found diverse applications in the photothermal therapy of cancer [1] and in electronic and optoelectronic devices like solar cells [2], optical filters [3], thermoelectric converters [4], and super ionic conductors [5] Indium selenide, a III–VI semiconductor, consists of Se–In– In–Se sheets which are two dimensionally arranged to give a hexagonal crystalline structure By virtue of such a layered structure, indium selenide exhibits highly anisotropic optical and electronic properties [6] Indium selenide is a potentially suitable material for solar photovoltaics and electrochemical devices like photodetectors [7], ion batteries [8], and solid solution electrodes [9,10] Similarly, copper indium diselenide (CIS) and related copper chalcopyrite semiconductors are among the most important photoabsorbing materials for polycrystalline thin film solar photovoltaics These direct band gap materials offer high absorption coefcients n Corresponding author Tel./fax: ỵ 44 161 2751411 E-mail address: paul.obrien@manchester.ac.uk (P O’Brien) http://dx.doi.org/10.1016/j.jcrysgro.2014.01.049 0022-0248 & 2014 Elsevier B.V All rights reserved (4105 cm À 1), greater photo-irradiation stability and very little/no toxicity [11] CuInSe2 has a direct band gap of 1.04 eV which is considerably lower than the optimal value for terrestrial solar cell applications whereas its gallium analogue copper gallium diselenide (CuGaSe2) has a band gap of 1.68 eV [12] Copper indium gallium diselenide (CIGS) may be considered as a pseudobinary alloy of ternary CuInSe2 and CuGaSe2 materials, in which indium (In) atoms in the CIS superlattice are gradually replaced by the gallium (Ga) atoms This system may be generally represented as CuIn1À xGaxSe2 and offers flexible band gap engineering of the material from 1.04 eV to 1.68 eV by gradual substitution of Ga for In atoms Recently, Jackson et al., have reported 20.1% and 20.3% efficiencies for CIGS thin-film solar cells [13] A number of stoichiometric compositions (CuSe, Cu2Se, CuSe2, Cu3Se2, Cu5Se4, Cu7Se4 etc.) and non-stoichiometric composition (Cu2 À xSe), have been reported for copper selenide [14–18] The copper selenide thin films have been deposited by using a variety of techniques like vacuum evaporation [19], solvothermal method [20], melting of elemental copper and selenium [21], electrodeposition [22], D.C magnetron sputtering [23],solution phase growth [24], chemical bath deposition [25] and chemical vapour deposition (CVD) [26] Similarly, the In2Se3 thin films have been grown by a number of techniques like elemental evaporation [27], spray pyrolysis [28], sol–gel synthesis [29], electrodeposition [30], molecular beam epitaxy [31] and MOCVD including LPCVD 40 S Mahboob et al / Journal of Crystal Growth 394 (2014) 39–48 and AACVD [32,33] The absorber layer in CIGS solar cells and the modules with record efficiency has been deposited by the coevaporation process [34] Moreover other techniques have also been used for deposition of CuInSe2 and related copper chalcopyrite thin films These techniques include molecular beam epitaxy (MBE) [35], chemical vapor deposition (CVD) [36], chemical bath deposition (CBD) [37], sputtering [38], successive ionic layer absorption and reaction (SILAR) method [39], electrodeposition [40], spray deposition [41], pulsed laser deposition [42] and microwave irradiation [43] Generally, the deposition of a metal selenide thin films is encountered with problems of obtaining a polyphasic mixture or the materials with bad orientation, unless expensive deposition techniques are employed It is still a challenge to precisely control the grain size, shape and the stoichiometric composition of deposited material, especially while scaling up the process CVD has a remarkable potential for scaling up the technology as has already been demonstrated in the process of deposition of self cleaning TiO2 coatings onto soda lime glass [44] The dilemma of finding chemical precursors with optimal volatility, however, limits the usefulness of the conventional CVD technique AACVD circumvents this difficulty and offers relatively better control over the stoichiometric composition of the deposited materials Marchand et al have recently reviewed diverse applications and advantages of the AACVD process in materials fabrication [45] Therefore, our previous efforts include precursor design and the deposition of semiconductor materials by a variety of techniques, especially AACVD We have successfully used a single source precursor approach for the deposition of good quality thin films of metal chalcogenides Previously, we have reported the deposition of Cu2 À xSe thin films by LP-MOCVD and AACVD using carbamato-compound Cu [E2CNMenHex]2 as a single source precursor [46] Our previous research efforts also include deposition of In2Se3and Ga2Se3thin films from [In{Se2CN(Me)Hex}3 [47], In[(SePiPr2)2N]2Cl [48], [Me2In(Se2PiPr2)2N], [Et2In(Se2PiPr2)2N] and [Me2Ga(SePiPr2)2N] precursors [49] We have also reported the deposition of CuInSe2, CuInS2, and CuGaS2 thin films using Cu(II) and In(III) complexes of methyl-n-hexyl-diselenocarbamate as dual-source precursors by LP-CVD and AACVD [50] Similarly, we have also used Cu(II) and In(III) complexes of iminobis(diisopropylphosphineselenide), for the deposition of CuInSe2 thin films by AACVD [51] Our previous efforts also include a facile and reproducible synthesis of air and moisture stable [HNEt3][iPr2PSe2] ligand and its complexes with a variety of metals [52] Herein, we report the deposition of phase pure polycrystalline thin films of In2Se3, Cu2À xSe, CuInSe2, CuGaSe2 and CuIn0.7Ga0.3Se2 from diisopropyldiselenophosphinato-metal complexes as precursors Experimental Chlorodiisopropylphosphine, triethylsilane, triethylamine, Se powder $ 100 mesh, indium(III) chloride, gallium(III) chloride, copper(II) chloride, copper(I) chloride and hexane were obtained from SigmaAldrich and used as received Synthesis of ligand salt [HNEt3][iPr2PSe2] and its complexes with indium(III), gallium(III) and copper(I) was carried out in accordance with the previously reported procedures [52] Solvents toluene and methanol were dried through distillation over sodium/benzophenone and calcium hydride prior to use All synthetic manipulations were carried out under nitrogen atmosphere by employing the Schlenk line techniques A glove box filled with nitrogen was used to handle pyrophoric and air sensitive chemicals (e.g GaCl3) The glassware was flame dried along with evacuation followed by purging with dry nitrogen to remove moisture before each experiment 1H NMR spectra were recorded on Bruker AC300 FT-NMR spectrometer and a Kratos Concept 1S instrument was used to record mass spectra Elemental analyses were performed on CHN Analyzer LECO model CHNS-932 Melting points were recorded using a Stuart melting point apparatus and are uncorrected 2.1 Deposition of thin films by AACVD The substrates used for the deposition of thin films were glass slides (1  cm) which were thoroughly cleaned to remove any possible contamination All AACVD experiments for the deposition of thin films were performed using a self designed AACVD Kit described elsewhere [53] In a typical experiment, 150 mg of the precursor (or a precursor mixture in the desired ratio in case of ternary and quaternary thin films) in 15 mL toluene was added in a two-necked 100 mL round-bottom flask with a gas inlet that allowed the carrier gas (argon) to pass through the solution and aid transport of the aerosols This flask was connected to the reactor tube by a piece of reinforced tubing A Platon flow gauge was used to control argon flow rate at 130 mL/min Six glass substrates were positioned in the reactor tube which was in turn placed in a Carbolite furnace A round-bottom flask containing the precursor solution was placed in a water bath just above the piezoelectric modulator of a PIFCO ultrasonic humidifier Carrier gas transferred thus generated aerosols to the hot zone of the reactor Both the solvent and the precursor underwent thermolysis at the hot substrate surface where the deposition of film took place as a result of thermally induced reaction Deposition was carried out at different temperatures i.e 300 1C, 350 1C, 400 1C, 450 1C and 500 1C at a constant argon flow rate on substrates for 1.5 h A Bruker D8 AXE diffractometer (Cu-Kα) was used to record p-XRD patterns of the thin films The samples were scanned from 20 degrees to 80 degrees, in a step size of 0.05 Edwards E-306A coating system was used for carbon coating of the thin films Film morphology was investigated by using a Philips XL 30 FEGSEM and film composition was studied by EDX analysis using a DX4 instrument AFM images were recorded on Veeco-CP II microscope Results and discussion The ligand salt [HNEt3][iPr2PSe2] was synthesized using literature procedure except that a 20% excess of triethylamine was used in the reaction Excess triethylamine ensures the availability of [HNEt3] ỵ in the reaction medium and suppresses the formation of bis(diisopropylselenophosphinyl)-selenide (R2PSe)2Se thus significantly improving the yield of reaction Reaction of the ligand salt [HNEt3][iPr2PSe2] with metal halides (CuCl, InCl3 and GaCl3) at room temperature yielded air and moisture stable complexes with a fair purity and in a good yield These complexes were characterized and subsequently used as precursors for the deposition of metal chalcogenide thin films 3.1 Thermogravimetric analyses Thermogravimetric analyses (TGA) were carried out to assess the thermal decomposition behaviour of the complexes TGA curves of the copper, indium and gallium complexes are shown in Fig The TGA curve of [Cu4(iPr2PSe2)4] shows that the copper precursor decomposes cleanly in one step at around 340 1C with residue (43.8%) in close accordance with the CuSe percentage (42.1%) in the precursor The TGA curve for [In(iPr2PSe2)3] shows that the complex decomposes in steps; at 350 1C (62% weight loss) and at 475 1C (5% weight loss) Above 480 1C the residue is 23.5%, which is in a good agreement with the calculated value for In2Se3 (24.8%) TGA analysis of [Ga(iPr2PSe2)3] demonstrates that S Mahboob et al / Journal of Crystal Growth 394 (2014) 39–48 Fig TGA curves showing decomposition behavior of (a) [Cu4(iPr2PSe2)4], (b) [Ga(iPr2PSe2)3] and (c) [In(iPr2PSe2)3] precursors decomposition of this complex is not clean and occurs in two steps Therefore, this complex may not be a suitable precursor for deposition of Ga2Se3 material, especially at a temperature below 500 1C This inference was later confirmed experimentally as AACVD experiments using this precursor alone gave no appreciable deposition of Ga2Se3 onto the substrates up to 500 1C 3.2 Deposition of copper selenide thin films Copper selenide thin films were deposited from [Cu4(iPr2PSe2)4] by AACVD at temperatures ranging from 300 1C to 500 1C At 300 1C, no deposition was observed on the substrates However, experiments at 350 1C and higher temperatures gave the uniform deposition of a black, shiny and well adhered material The powder X-ray diffraction (p-XRD) patterns of thin films grown at 350 1C, 400 1C, 450 1C and 500 1C are shown in Fig 2A Analysis of the p-XRD patterns revealed that the berzelianite phase of Cu2 À xSe (ICDD pattern 00-006-680) was deposited at all temperatures No peaks corresponding to other phases of copper selenide were observed in the diffraction pattern Relatively narrow and sharper peaks were observed for thin films deposited at 450 1C and 500 1C This indicates a larger grain size and better crystallinity of the Cu2 À xSe material deposited at higher temperatures The surface morphology of as deposited films was studied using scanning electron microscopy Representative SEM images of Cu2 À xSe films deposited at various temperatures are shown in Fig 2B It was evident that the shape of the deposited grains varies significantly with the deposition temperature Randomly distributed globular grains are formed at 350 1C whereas deposition at higher temperature yields a granular and predominantly triangular morphology At 500 1C, large grains with multiple triangular faceting were clearly visible EDX analysis shows deviation from normal stoichiometric ratio of 2:1 for copper and selenium Materials obtained at 350 1C and 400 1C temperatures were slightly Cu deficient having Cu to Se ratio of 1.92:1 while those obtained at 450 1C and 500 1C were even more Cu deficient having 1.85:1 stoichiometry A summary of EDX results of the thin films deposited at different temperatures is given in Table 3.3 Deposition of indium selenide thin films [In(iPr2PSe2)3] was used as a single source precursor (SSP) for the deposition of In2Se3 thin films at temperatures ranging from 300 1C to 500 1C AACVD experiments at all temperatures resulted 41 in the deposition of a reddish black indium selenide material; however, the best deposition was achieved at 450 1C The films deposited at this temperature were well adhered to the substrate and successfully passed the scotch-tape test Crystallographic phase of the deposited material was determined by using p-XRD technique Fig 3A shows p-XRD patterns of the thin films deposited at different temperatures The p-XRD patterns revealed that the material deposited at all the temperatures corresponds to γ-phase of In2Se3 (standard ICDD pattern 00-040-1407) which was preferentially oriented along (1 0) plane The crystallinity of the In2Se3 material was reflected by sharpness of the XRD peaks Furthermore, appearance of no additional peaks indicates that material is significantly pure and monophasic as no other phases of indium selenide were observed SEM images of the as deposited thin films (Fig 3B) were obtained to study the surface morphology and microstructure of the deposited material The SEM images showed uniform coverage of the substrates with highly crystalline grains deposited Different morphologies of the grains were obtained at different deposition temperatures The deposition at 350 1C and 400 1C yielded flake like structures whereas cylindrical grains with approximate dimensions of 1.27–1.36 μm  1.79–1.95 μm were deposited at 450 1C The deposition experiments at 500 1C resulted in randomly oriented plates A homogeneous distribution of grains on the surface was clearly evident in all the films The stoichiometric composition of the material was determined by EDX analysis which showed that the material obtained is slightly Se rich, the ratio of indium to selenium being 2.05:3.5 Furthermore, no appreciable difference in the stoichiometric composition of the individual grains was observed Optical band gap of the films deposited at 450 1C was determined by extrapolating the straight line part of the (αthυ)2 vs hυ curve to the hυ axis, where (αthυ)2 ¼0, and was found to be $ 1.82 eV The bandgap values of different thin films deposited at 450 1C are given in Table 3.4 Deposition of CuInSe2 thin films CuInSe2 thin films were deposited from 1:4 M equivalents of [Cu4(iPr2PSe2)4] and [In(iPr2PSe2)3] precursors A very poor coverage of the film was obtained at 300 1C However, the deposition experiments at 350 1C to 450 1C yielded weakly adhered, black and shiny films which did not qualify the scotch tape test The p-XRD patterns of the thin films were recorded to determine the crystallographic phase of the material p-XRD patterns (Fig 4A) demonstrated that tetragonal phase of CuInSe2 (standard ICDD pattern 01-075-0107) was deposited at all temperatures In all the cases, the deposited material had a preferred orientation along (1 2) plane which is typical for ternary copper chalcopyrite compounds deposited by CVD Quite sharp peaks in the p-XRD pattern especially at a higher temperature reflected an improved crystallinity of the material, whereas a pure and monophasic nature of deposited material was demonstrated by the absence of any additional peaks due to possible binary phases of copper and/or indium selenide The microstructure of the thin films was studied with the help of scanning electron microscopy The SEM images (Fig 4B) show that the film deposited at 300 1C consists of clusters of an undefined shape randomly distributed onto the substrate However, at 350 1C to 450 1C, the films exhibited good coverage with material having predominantly rice like morphology with uniform grain size and well defined grain boundaries especially at 450 1C EDX analysis showed that the ratio of Cu:In:Se was close to 1:1:2 for CuInSe2 stoichiometry in all the films About 3% of phosphorus contamination was found on the films grown at a lower temperature (300 1C, and 350 1C); however 42 S Mahboob et al / Journal of Crystal Growth 394 (2014) 39–48 Fig (A) p-XRD patterns of as deposited Cu2 À xSe thin films from [Cu4(iPr2PSe2)4] precursor at temperatures (a) 350 1C, (b) 400 1C, (c) 450 1C and (d) 500 1C Vertical lines below show the standard ICDD pattern 00-006-680 for berzelianite phase of Cu2 À xSe (B) SEM images of as deposited thin films of Cu2 À xSe at (a) 350 1C, (b) 400 1C, (c) 450 1C and (d) 500 1C no such contamination was found on the films deposited at higher temperatures AFM was also used to study surface morphology of the CuInSe2 films AFM images of CuInSe2 thin films deposited at 400 1C are shown in Fig 4C The images revealed that deposited material consists of uniform sized granules which are homogeneously distributed onto the surface of glass substrates as agglomerates Root mean square roughness of the thin film surface was calculated by acquiring a number of scans from different areas of the film and found to be 130.8 nm The optical band gap of the films deposited at 450 1C was found to be $ 1.13 eV whereas the reported band gap energies of CuInSe2 are 1.05 eV, 1.13 eV and 1.2 eV [54] 3.5 Deposition of CuGaSe2 thin films [Cu4(iPr2PSe2)4] and [Ga(iPr2PSe2)3] precursors were used in a 1:4 M equivalents respectively to carry out the deposition of CuGaSe2 thin films at the temperatures ranging from 350 1C to 500 1C Poor films were obtained at 350 1C which gave a poor diffraction in p-XRD Greenish black films were obtained at 400–450 1C deposition temperature whilst the film deposited at 500 1C showed a very fine black powder layer on the surface of substrates which may be attributed to an excess of the same deposited material p-XRD patterns of as-deposited thin films of CuGaSe2 are shown in Fig 5A The films deposited at lower temperature did not give a good diffraction pattern due to low S Mahboob et al / Journal of Crystal Growth 394 (2014) 39–48 43 Table EDX analyses results of thin films deposited at different temperatures Material Cu2 À xSe, berzelianite (ICDD 00-006-680) γ-In2Se3 (ICDD 00-040-1407) CuInSe2 (ICDD 01-075-0107) CuGaSe2 (ICDD 00-035-1100) CuIn0.7Ga0.3Se2 (ICDD 00-035-1102) Deposition temperature (1C) 350 400 450 500 350 400 450 500 350 400 450 500 350 400 450 500 350 400 450 500 crystallinity of the material However, broader peaks were obtained for the thin film deposited at 400 1C These p-XRD patterns demonstrate that the material is not very crystalline and consists of small grains No extra peaks were observed in the diffraction pattern recorded at 400 1C, but some extra peaks assignable to copper selenide were found in the diffraction pattern of the film deposited at 450 1C At 500 1C, a sharp diffraction pattern was obtained which showed deposition of tetragonal phase of chalcopyrite CuGaSe2 (ICDD 00-035-1100) The surface morphology of the films was studied with the help of scanning electron microscopy SEM images of the thin films deposited at different temperatures are shown in Fig 5B It was observed that morphology of CuGaSe2 thin films was strongly influenced by the deposition temperature As expected, films deposited at 350 1C showed deposition of very small globules which were not crystalline enough to give a good diffraction pattern SEM images of the thin films deposited at 400 1C and 450 1C reveal the formation of nano wires These wires are less dense and randomly distributed onto the surface of substrate at 400 1C while deposition at 450 1C yielded the densely covered and well adhered films The deposition at 500 1C resulted in the formation of randomly oriented globular structures of uniform size EDX analyses showed a stoichiometric ratio closer to the expected 1:1:2 ratio for copper, gallium and selenium However, a slight excess of Se was found in the films deposited at lower temperatures Phosphorus contamination was observed in the thin films deposited below 450 1C, however no considerable phosphorous contamination was observed in the film deposited at 500 1C Surface profile of the films was further examined with the help of atomic force microscopy (AFM) Two-dimensional and three dimensional AFM images of CuGaSe2 thin film deposited at 500 1C are shown in Fig 5C, which shows a root mean square roughness of 41.39 nm for the surface of as-deposited film An optical band gap of the film deposited at 450 1C was measured by the direct band gap method and found to be about 1.67 eV 3.6 Deposition of CuIn0.7Ga0.3Se2 thin films Thin films of CIGS were deposited onto the glass substrates by using different molar equivalents of [Cu4(iPr2PSe2)4, [In(iPr2PSe2)3] and [Ga(iPr2PSe2)3] to obtain films of varying stoichiometric combinations The deposition experiments were carried out using EDX analyses results atomic percentage (%) Cu In Ga Se P 64.0032 64.0249 61.6697 62.0016 – – – – 23.6943 23.5617 24.3513 24.5446 22.7925 22.9745 24.2922 24.9532 24.7640 25.0129 25.0000 25.1274 – – – – 36.7423 37.0268 36.9369 36.8077 24.0042 24.0212 24.8945 24.9122 – – – – 17.5631 17.3409 17.5000 17.3169 – – – – – – – – – – – – 23.2655 23.0291 24.3362 23.1986 7.7399 7.9226 7.5000 7.6280 35.9968 35.9751 38.3303 37.9984 63.2577 62.9732 63.0631 63.1923 49.3001 49.1854 50.7542 50.5432 49.4709 51.9901 51.3716 51.8482 49.9330 49.7236 50.0000 49.9177 – – – – – – – – 3.1004 3.2317 – – 1.4711 1.1063 – – – – – – 1:1:1 M, 1:2:2 M and 1:2:4 M ratios of copper, indium and gallium precursor, respectively, at temperatures ranging from 350 1C to 500 1C For all molar ratios, black shiny films were obtained Previously, we have reported the colloidal synthesis of nanoparticles from these precursors [55] It was demonstrated that by varying the molar ratios of copper, indium and gallium precursors, different stoichiometric compositions of CuIn1 À xGaxSe2 nanoparticles could be obtained However, in case of the thin films, p-XRD patterns of the thin films deposited from different molar combinations of precursors revealed that more than one phase of material was deposited in the case of 1:1:1 M and 1:2:4 M ratios of Cu, In and Ga precursors, respectively Besides CIGS, CuGaSe2, Cu2 À xSe and CuInSe2 were present as impurities Only in the case of deposition involving 1:2:2 M ratios of copper, indium and gallium precursors, respectively, a phase pure material with no traceable impurities was deposited The p-XRD patterns (Fig 6A) obtained in this case were assignable to a tetragonal CuIn0.7G0.3Se2 crystallographic phase (ICDD pattern 00-035-1102) with preferred orientation along (1 2) plane No other stoichiometric compositions of CIGS could be obtained The well defined and sharp diffraction peaks indicated that the material was sufficiently crystalline and purity of as-deposited chalcopyrite material was evident from the absence of any additional diffraction peaks of possible binary phases or impurities The SEM images, as shown in Fig 6B, revealed that the films were uniformly covered with material having well defined shapes of grains It was further observed that the shapes of grains are influenced by the deposition temperature Randomly oriented grains of indefinite geometry were deposited at 350 1C, while evenly distributed, uniform sized flakes like crystallites were deposited at 400 1C to 500 1C A high magnification view of the film deposited at 450 1C is given in Fig 6B(e) EDX data of CIGS across the entire film revealed a uniform composition that was fairly compatible with the stoichiometric ratio expected for CuIn0.7Ga0.3Se2 Surface roughness of the films is decreased as larger and more uniform grains are deposited at higher deposition temperatures The same is observed from AFM analysis (Fig 6C), which revealed that the root mean square roughness of CIGS deposited at 400 1C was 55.46 nm while CIGS deposited at 450 1C had a root mean square roughness of 44.50 nm An optical band gap of CuIn0.7Ga0.3Se2 material deposited at 450 1C from 1:2:2 M equivalents of 44 S Mahboob et al / Journal of Crystal Growth 394 (2014) 39–48 Fig (A) p-XRD patterns of as deposited In2Se3 thin films from In(iPr2PSe2)3] precursor at temperatures (a) 300 1C, (b) 350 1C, (c) 400 1C and (d) 450 1C Vertical lines below show the standard ICDD pattern 00-040-1407 for γ-In2Se3 (B) SEM images of as deposited In2Se3 thin films at (a) 300 1C, (b) 350 1C, (c) 400 1C and (d) 450 1C Table Bandgap values of different thin films deposited at 450 1C Thin film material (deposited at 450 1C) Bandgap (eV) (calculated value) Bandgap (eV) (literature value) Reference In2Se3 CuInSe2 CuGaSe2 CuIn0.7Ga0.3Se2 1.82 1.13 1.67 1.46 1.82 1.05, 1.13, 1.20 1.68 1.05 to 1.65n [48] [54] [12] [56] n The band gap of CuIn1 À xGaxSe2 thin films varies from 1.05 to 1.65 eV with increasing Ga copper, indium and gallium precursors, respectively, was found to be 1.46 eV The values of band gap energies reported in literature for CIGS vary from 1.04 eV to 1.68 eV depending upon the composition SEM images of the thin films deposited from 1:1:1 M equivalents of copper, indium and gallium precursors revealed the presence of additional phases, especially Cu2À xSe and CuInSe2 along with grains of CIGS material Deviation from targeted stoichiometry was observed in all these experiments Attempts to deposit gallium rich CIGS thin films by increasing the molar ratio of gallium precursor (by using 1:2:4 M ratio for copper, indium and gallium precursors) proved unsuccessful In this case, additional phases of CuGaSe2 and Ga2Se3 were obtained instead These results fully conform to those deduced from aforementioned p-XRD analysis of the films Conclusions The deposition of In2Se3, Cu2À xSe, CuInSe2, CuGaSe2 and CuInGaSe2 (CIGS) thin films from diisopropyldiselenophos-phinato-metal S Mahboob et al / Journal of Crystal Growth 394 (2014) 39–48 45 Fig (A) p-XRD patterns of as deposited CuInSe2 thin films from 1:4 M ratios of copper and indium precursor at temperatures (a) 300 1C, (b) 350 1C, (c) 400 1C and (d) 450 1C indexed with standard ICDD pattern 01-075-0107 (B) SEM images of as deposited thin films of CuInSe2 at (a) 300 1C, (b) 350 1C, (c) 400 1C and (d) 450 1C (C) 2D and 3D AFM images showing surface roughness of as deposited CuInSe2 thin film deposited at 450 1C complexes by AACVD has been demonstrated in this study [In (iPr2PSe2)3] and [Cu4(iPr2P2Se2)4] complexes deposited monophasic γ-In2Se3 and Cu2 À xSe films, respectively Both of the ternary materials (CuInSe2, CuGaSe2) were deposited in the tetragonal phase and they showed a preferred orientation along (1 2) plane in their p-XRD Different molar ratio combinations of the copper, indium and gallium precursors for the deposition of CIGS resulted in the mixed phase material except in a molar ratio of 1:2:2 which 46 S Mahboob et al / Journal of Crystal Growth 394 (2014) 39–48 Fig (A) p-XRD pattern of CuGaSe2 thin films deposited from 1:4 M ratios of Cu and Ga precursors at (a) 350 1C, (b) 400 1C, (c) 450 1C and (d) 500 1C Vertical lines below show standard ICDD pattern 00-035-1100 for CuGaSe2 (B) p-XRD pattern of as deposited CuGaSe2 thin films at (a) 350 1C, (b) 400 1C, (c) 450 1C and (d) 500 1C from 1:4 M ratios of Cu and Ga precursors (C) 2D and 3D AFM images of as grown CuGaSe2 thin films from 1:4 equivalent of [Cu4(iPr2P2Se2)4] and [Ga(iPr2PSe2)3] precursors at 450 1C S Mahboob et al / Journal of Crystal Growth 394 (2014) 39–48 47 Fig (A) p-XRD pattern of as deposited CuIn0.7Ga0.3Se2 thin films at (a) 300 1C, (b) 350 1C, (c) 400 1C, (d) 450 1C and (e) 500 1C from 1:2:2 M equivalents of [Cu4(iPr2P2Se2)4], [In(iPr2PSe2)3] and [Ga(iPr2PSe2)3], respectively, indexed with standard ICDD pattern 00-035-1102 (B) SEM images of as deposited CuIn0.7Ga0.3Se2 thin films at (a) 350 1C, (b) 400 1C, (c) 450 1C and (d) 500 1C (e) Higher magnification image of thin film deposited at 450 1C showing individual CIGS grains (C) (a) 2D, (b) 3D AFM images of as deposited CuIn0.7Ga0.3Se2 at 450 1C with Root mean square roughness 44.50 nm, (c) 3D AFM image of CuIn0.7Ga0.3Se2 thin film deposited at 400 1C (d) 3D AFM image of nano indent type microstructures found at film surface produced phase pure CuIn0.7G0.3Se2 Significant differences were noticed in the morphology of the thin films with the deposition temperature 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equivalent of [Cu4(iPr2P2Se2)4] and [Ga(iPr2PSe2)3] precursors at 450... case of the thin films, p-XRD patterns of the thin films deposited from different molar combinations of precursors revealed that more than one phase of material was deposited in the case of 1:1:1... 500 1C 3.2 Deposition of copper selenide thin films Copper selenide thin films were deposited from [Cu4(iPr2PSe2)4] by AACVD at temperatures ranging from 300 1C to 500 1C At 300 1C, no deposition