Microsoft Word - 37-49 https://doi.org/10.30526/31.1.188 Physics | 37 2018) عام 1(العدد ) 31(لمجلد ا مجلة إبن الهيثم للعلوم الصرفة و التطبيقية Ibn Al-Haitham J. for Pure & Appl. Sci. Vol.31 (1) 2018 Investigation of the Structural, Optical and Electrical Properties of AgInSe2 Thin Films Iman Hameed Khudayer Bushra Hashem Hussein Ali Mohammed Hamid Mustafa Ayser Jumah Ibrahim Dept. of Physics/ College of Education for Pure Science (Ibn Al-Haitham) / University of Baghdad demanphd2005@gmail.com Received in:12/June/2017, Accepted in:2/October/2017 Abstract The Silver1Indium1Selenide (AgInSe2) (AIS) thin1films of (3001±20) nm thickness have been1prepared2from the compound alloys2using thermal evaporation2 technique onto the glass2substrate at room temperature, with a deposition rate2(3±0.1) nm2sec-1. The2structural, optical and electrical3properties have been studied3at different annealing3temperatures (Ta=450, 550 and 650) K. The amount3or (concentration) of the elements3(Ag, In, Se) in the prepared alloy3was verified using an energy dispersive3x-ray spectrometer (EDS)3technology. X-ray diffraction3analysis shows that AIS alloy prepared as (powder) and the thin films3are polycrystalline of tetragonal3structure with preferential orientation3(112). The crystalline3size increases as a function3of annealing temperature. The atomic force3microscope (AFM) technique was used to examine3the topography and estimate3the surface roughness, also the average grain3size of the films. The results show3that the grain size increases3with annealing3temperature. The optical4band gap of the films lies4in the range 1.6-1.9 eV. The films4appear to be4n-type indicating that the electrons4as a dominant charge4carrier. The electrical conductivity4increases with a corresponding4increase in annealing4temperature. Keywords: AIS, 4Films, 4Structural, Optical, 4Electrical conductivity, Hall4Effect, Thermal4Evaporation. https://doi.org/10.30526/31.1.188 Physics | 38 2018) عام 1(د العد ) 31(لمجلد ا مجلة إبن الهيثم للعلوم الصرفة و التطبيقية Ibn Al-Haitham J. for Pure & Appl. Sci. Vol.31 (1) 2018 Introduction In recent4years, considerable4efforts have been4made to grow4device-quality thin4films by optimization of growth4parameters for applications4in optoelectronic devices. The ternary semiconductor4compounds with the formula4AIBIIICVI2 such4as CuAlS2, AgAlSe2, etc. have been widely4investigated because4of their potential applications4in electro-optic, the chalcopyrite4type crystals the most intensive4studies have been4carried out in the series4of I− III−VI2 family compounds4where Cu is involved4as a group I element, very few4works have appeared in literature where the group I element is Ag4[1]. AIS semiconductors4have been produced by several4techniques5such as: co-evaporation5[2,3], ultra-high vacuum5pulsed laser deposition [4], horizontal5Bridgman method [5], molecular beam5epitaxial [6], vertical gradient temperature5freezing method [7] and solid5state microwave irradiation5[8]. In this work, we have5prepared Ag-In-Se5thin films by thermal evaporation5technique, followed by an adequate5 annealing treatment. Experimental The alloy5of AgAlSe2 was obtained by fusing5the mixture of the appropriate amount5of the elements Ag, In and Se of high purity (99.999%) in an evacuating fused quartz5ampoules with5(2×10-35Torr), heated at (1200 K) for five5hours. The films of 300±20 nm thickness were deposited5by the thermal evaporation technique5at room temperature5using the Edward5coating unit model (E 306) with molybdenum5boat. Energy5dispersive x-ray spectrometer (EDS) was used to investigate5the amount or (concentration5) of the elements5(Ag, In, Se) of AgInSe25 alloy. The crystal5structure of the alloy and films was characterized5by using X-ray diffraction5(XRD) by (Shimadzu60005X-ray Diffraction) with the copper5target of the wavelength5(λ=1. 5406) Ǻ. Lattice constants, crystalline size5were specified, the inter planar5spacing dhkl (Å) between consecutive5parallel planes was measured5by Bragg’s law5[9]: n λ= 2θ dhkl Sin(θ) …………………………………………. (1) Where, n5is the order of diffraction and θ5is the angle of incidence. The average crystalline5size can be estimated5using the Scherrer’s Formula5[10]: )2....(.................................................. cos 94.0 . )( BFWHM RayXSC    Where, β is the full width5at half maximum5 intensity in radians. (AFM) was employed5to investigate the surface morphology5of the AgInSe2 films5as a device5type of (SPM5-AAA3000 contact5mode spectrometer, Angstrom). Optical measurement5 has been constructed using5 UV-Visible 18005spectrophotometer. The thickness (t) of all prepared films was measured5 by using the weighing5method according to the following5relation [11]: t= m / A.ρ ……………………………………. (3) Where; m, ρ, A were the mass, density and area of the films. Using a sensitive balance5 whose sensitivity of the order5 (10-4) gm. The optical5 absorption spectrum5was utilized to define the optical energy5gap (Egopt) eV using Tauc5 formula [12]: αhν=B (hν –Egopt)1/r ………………………………………….(4) Where, B is a constant, hν is the photon5energy (eV) and r is constant, that it may take values52, 3, 1/2, 3/2 depending on the material5and the type of the optical transition5. The absorption5coefficient (α) value can be computed5from the formula [13]: https://doi.org/10.30526/31.1.188 Physics | 39 2018) عام 1(د العد ) 31(لمجلد ا مجلة إبن الهيثم للعلوم الصرفة و التطبيقية Ibn Al-Haitham J. for Pure & Appl. Sci. Vol.31 (1) 2018 )5....(................................................................................303.2 t A  Where, A is the optical5 absorbance. The refractive5index value can be calculated from5the formula [14]:   )6.........(........................................ 1 1 1 4 2 1 2 2                  R R k R R no where k represents5the extinction coefficient, which is calculated5by the relation [14]: )7......(................................................................................ 4  k The real5εr and imaginary5εi part of dielectric5constant can be calculated by using the following5 equations [15]: )8(................................................................................ir i  )9(................................................................................20 2 0 knr  )10...(................................................................................2 00 kni  The electrical5resistance (Ro) of (AIS) films has been measured5as a function of temperature5 within the range (298-503) K by using Keithly5616 Digital Electrometer and electrical5oven, then the resistivity5 (ρ) has been calculated5 using the formula [16]: )11....(............................................................0 L tb R   Where; b is the electrode5width and L is the distance5 between two Al electrodes. The conductivity (σd.c) associated5with the resistivity5as in the equation [16]: )12...(............................................................ 1 .   cd Hall Effect5measurements have been managed5by Van der Pauw5(Ecopia HMS -3000) to determining majority5 carrier concentrations, type of carrier5and their mobility5 in thin5films. Result and discussion Energy6dispersive x-ray spectrometer6(EDS) used to examine the amount6or (concentration) of the elements6(Ag, In, Se) in the alloy. The results are shown in figure (1) and table (1). Figure (2) shows the XRD6pattern of (AIS) bulk powder, which illustrates6that the AgInSe2 was a chalcopyrite material in polycrystalline (tetragonal phase) structure as it is compared6with the standard6values in ICDD6cards. The spectrum6is considered to exhibit sharp6peaks at (112),(200), (220), (204), (312), (116),(400), (316), and (424) corresponding to 2θ values equal to 25.72, 29.45, 41.95, 42.92, 49.84, 51.51, 60.72, 68.42 and 77.12 respectively. The X-ray diffraction6parameters inter planar spacing (d), Miller6indices and crystalline6size for AgInSe2 alloy6are listed in table (2), they prefer orientation6at (112) planes. Whereas from the X-ray diffraction6patterns of AgInSe2 thin6films with different annealing6temperatures, one can observe that the thin films6have the polycrystalline6tetragonal structure7as shown in figure (3). The figure indicates that the patterns7include three sharp peaks7referred to (112), (220) and (312) direction. As well, this figure confirms7that the preferential orientation is in the7(112) direction. The structural parameters7of annealed AgInSe2 thin7films with different annealing7temperatures were illustrated in table (3). The crystallite7size has been estimated7 of the FWHM value of the https://doi.org/10.30526/31.1.188 Physics | 40 2018) عام 1(د العد ) 31(لمجلد ا مجلة إبن الهيثم للعلوم الصرفة و التطبيقية Ibn Al-Haitham J. for Pure & Appl. Sci. Vol.31 (1) 2018 (112) peak7by using Scherrers equation and is observed,7it increased with Ta as shown in table (3). These results were matched with [3,17]. By increasing the Ta the locations of the measured diffraction7peaks do not change significantly7, but the intensities7of the peaks increase. This is due to the improvement7of crystalline of the films. Figure (4) shows the three7-dimensional (3D) of AgInSe2 thin films with different Ta. From this figure, it can be deduced7that these films have spherical7grains granting7the smooth surface7morphology. The values of surface roughness7and the grain sizes7are calculated. It has been7observed that a surface7roughness were equal to (0.608, 0.936,1.65 and 0.809) for different7Ta (RT, 450,550 and 650) K respectively. The grain8size has been observed (86.68, 90.49, 106.54 and 68.06) for (RT, 450, 550 and 650) K respectively. Therefore, the average8diameter of AIS thin8film with annealing temperature8550K (see Fig. 4, c) is larger than the AIS thin film (Figure 4, a, b, d). The absorbance8and transmittance8spectrum of AIS thin8film were evaluated as a function8of wavelength at different annealing8temperatures as in Figure (5). This figure believed that the absorbance8increases in the visible wavelength range as a function of annealing8temperature. The behavior of the transmittance spectra8is opposite completely8to that of the 8absorbance spectra. From figure (6), we can observe8that the α values, which were calculated using equation8(4), indeed, own high amount reached8above (104) cm-1. It was pointed that the α values in general increases8as a function of annealing8temperature, which is attributed to an increase8in absorbance of used films. From table (4) we found8that the value of α increases from (5.8-6.6) ×104cm-18with the increase of Ta. The value of Egopt decreases 8(from 1.8 to 1.6) eV and then increases to (1.9) eV with the increase of Ta as shown in table (4) and figure (6). The decrease8in the band gap8(Egopt) values may be describable of the increase8in defect states near the bands, this result8is in agreement8with ref. [3]. The Variation8of optical constants with photon8energy for AgInSe2 thin films at different8annealing temperatures is shown in figure (7), such that, refractive8index (a) extinction8coefficient (b) real (c) and imaginary8part of the dielectric constant (d). Table (4) indicates8that n valuable decreases with the rise of Ta. This behavior maybe because of the decreasing8in the reflection, which the refractive index8in turn depends on it. Extinction coefficient (k) in general increment8with Ta this is attributed to the same reason mentioned previously in the absorption8coefficient, because the behavior of k is similar8to α. The variables of εr and εi versus8photon energy at different8Ta are shown in figure 8(c & d). The behavior of εr is similar to that of the refractive index8because of the small value of k2 compared8with n2, while εi behavior is similar8to that of extinction coefficient8because it mainly depends on the k value, which is related to the variation9of absorption coefficient. The variables9of εr and εi with different8annealing temperatures film are non10-systematic. This means that this material10possesses a specialized property10with Ta. We can deduce from the variation10of the resistivity verse annealing10temperature for all samples of AIS films, that the resistivity values decrease10as the Ta rises due to the improvement10in the film construction. We believe that there was a reduce in dangling10bonds, defects like vacancy sites, and point10defect in the film structure, therefore10the resistivity of the films decreases from (1.32 Ω.cm to 0.30 Ω.cm) as the Ta increases10from ( RT to 550 K) as shown in Figure (8), which presented10a plot of lnσ versus 1031/T for different Ta. From this figure10the activation energy can be determined. Electrical10conductivity increases as the Ta enlarges because of the rise in the number10of available transport charge carriers. We can notice10from figure (8) that all AIS films have two mechanisms10for electrical conductivity which means that there are two mechanisms of transport of free carriers with two10values of the activation energy (Ea1, Ea2) each one predominating in a different temperature10range. The electrical conductivity10of these films is affected by the transport10of free carriers in extended10states beyond the mobility edge at higher temperature ranges10(403-473) K, as well https://doi.org/10.30526/31.1.188 Physics | 41 2018) عام 1(د العد ) 31(لمجلد ا مجلة إبن الهيثم للعلوم الصرفة و التطبيقية Ibn Al-Haitham J. for Pure & Appl. Sci. Vol.31 (1) 2018 as carriers excited into the localized10states at the edge of the band10and hopping10at other range of temperature (300-393) K [13] as shown in Table (5). The type of charge10carriers, concentration (n) and Hall mobility (μH) has been estimated10from Hall measurements. These values are listed in Table (6). The negative sign10of the Hall coefficient10indicates that the conductive nature of the film is n-type, i.e. electrons10are the majority charge carriers, this result is in agreement with ref. [18], i.e Hall10voltage decreases with the increase of the current. The carrier concentration10of the order 1017cm-3 is in a good agreement with refs [3,19]. We can notice10from Table (6) that the carrier concentration10and mobility increase with increase10of Ta. Table (1): The composition of AgAInSe2 alloy determined by (EDS) Test (Wt%) Calculated (Wt%) 28.188 28.337 Ag 30.085 30.162 In 41.38 41.491 Se Table (2): Structural10parameters of AgInSe2 alloy Std.) (Deg.) 2θ (Exp.) (Deg.) dhkl (Std.) (Å) dhkl (Exp.) (Å) hkl 25.726 25.727 3.46 3.45 (112) 29.355 29.45 3.04 3.03 (200) 41.96 41.95 2.151 2.15 (220) 42.97 42.92 2.103 2.105 (204) 49.96 49.84 1.824 1.828 (312) 51.469 51.51 1.774 1.772 (116) 60.808 60.725 1.522 1.523 (400) 68.708 68.42 1.365 1.369 (316) 77.39 77.12 1.232 1.23 (424) Table (3): Experimental10XRD data for AgInSe2 thin films at different Ta. T (K) 2θ (Deg.) dhkl (Exp.) (Å) hkl FWHM (Deg.) C.S (nm) Ta RT 25.72 3.458 (112) 0.472 17.127 41.95 2.15 (220) 49.84 1.828 (312) 450 25.75 3.455 (112) 0.400 21.277 41.98 2.14 (220) 49.89 1.825 (312) 550 25.8 3.449 (112) 0.211 40.336 42.1 2.143 (220) 49.92 1.824 (312) 650 25.82 3.446 (112) 0.376 22.637 42.3 2.134 (220) https://doi.org/10.30526/31.1.188 Physics | 42 2018) عام 1(د العد ) 31(لمجلد ا مجلة إبن الهيثم للعلوم الصرفة و التطبيقية Ibn Al-Haitham J. for Pure & Appl. Sci. Vol.31 (1) 2018 49.95 1.823 (312) Table (4): Optical constant10for AgInSe2 thin films at different Ta. Table (5): Values of D.C conductivity and activation1energies for AgInSe2 thin films at different10 Ta. Measurement temp. σ (Ω.cm)-1 Ea1 (eV) Tem.range (K) Ea2 (eV) Tem.range (K) RT 0.755 0.043344 300-393 0.17544 403-473 Ta(K) 450 1.221403 0.051084 300-393 0.176128 403-473 550 3.320117 0.052374 300-393 0.178042 403-473 650 2.013753 0.051417 300-393 0.176022 403-473 Table (6); Hall parameters10for AgInxe2 thin films at different Ta. Measurement temp. R(H) µH(cm2/V.S) n (cm-3) RT -22.32 16.85 2.8E+17 Ta(K) 450 -12.2549 14.96817 5.1E+17 550 -7.467145 24.79179 8.37E+17 650 -9.057971 18.24052 6.9E+17 Optical constant at λ=410nm Measurement temp. Egopt (eV) α×104 (cm)-1 n k εr εi RT 1.8 5.8 1.34 0.19 1.77 0.51 Ta (K) 450 1.75 6.17 1.24 0.2 1.5 0.54 550 1.6 6.6 1.2 0.21 1.39 0.51 650 1.9 4.68 1.61 0.15 2.5 0.36 https://doi.org/10.30526/31.1.188 Physics | 43 2018) عام 1(د العد ) 31(لمجلد ا مجلة إبن الهيثم للعلوم الصرفة و التطبيقية Ibn Al-Haitham J. for Pure & Appl. Sci. Vol.31 (1) 2018 In te n s it y ( C o u n t/ s e c ) Figure (1): EDS patterns10for AgInSe2 alloy. Figure (2): X-ray diffraction10pattern of AgInSe2 alloy. (112) (200) (220) (204) (400) (424) (316) (312) (116) https://doi.org/10.30526/31.1.188 Physics | 44 2018) عام 1(د العد ) 31(لمجلد ا مجلة إبن الهيثم للعلوم الصرفة و التطبيقية Ibn Al-Haitham J. for Pure & Appl. Sci. Vol.31 (1) 2018 Figure (3): X -ray diffraction pattern10of AgInSe2 thin film with a thickness (t=300nm) annealed at different Ta. Figure (4): 3D Atomic10force microscopy (AFM) of AgInSe2 thin film with a thickness (t=300nm) annealed at different Ta. In te n s it y ( C o u n t/ s e s ) RT 450 K 550 K 650 K (112) (200) (312) (a) RT (d) 650K (c) 550K (b) 450K 150K https://doi.org/10.30526/31.1.188 Physics | 45 2018) عام 1(د العد ) 31(لمجلد ا مجلة إبن الهيثم للعلوم الصرفة و التطبيقية Ibn Al-Haitham J. for Pure & Appl. Sci. Vol.31 (1) 2018 Figure (5): The Absorbance and Transmittance10spectrum of AgInSe2 thin film with a thickness (t=300nm) annealed at different Ta. https://doi.org/10.30526/31.1.188 Physics | 46 2018) عام 1(د العد ) 31(لمجلد ا مجلة إبن الهيثم للعلوم الصرفة و التطبيقية Ibn Al-Haitham J. for Pure & Appl. Sci. Vol.31 (1) 2018 Figure (6): (a) variation10(αhυ)2 verse photon energy, (b) absorption coefficient verse photon energy10for AgInSe2thin films at different annealing temperatures. https://doi.org/10.30526/31.1.188 Physics | 47 2018) عام 1(د العد ) 31(لمجلد ا مجلة إبن الهيثم للعلوم الصرفة و التطبيقية Ibn Al-Haitham J. for Pure & Appl. Sci. Vol.31 (1) 2018 Figure (7): Variation10of refractive index (a) Extinction10coefficient(b) real (c) and imaginary10part of dielectric constant (d) with photon energy for AgInSe2 thin films10at different annealing temperatures. Figure (8): Ln(σ) versus1reciprocal of temperature for AgInSe2 films at different Ta. Conclusions https://doi.org/10.30526/31.1.188 Physics | 48 2018) عام 1(د العد ) 31(لمجلد ا مجلة إبن الهيثم للعلوم الصرفة و التطبيقية Ibn Al-Haitham J. for Pure & Appl. Sci. Vol.31 (1) 2018 A. AgInSe2 alloy5was prepared successfully and used for preparation5of thin films by thermal evaporation5method. B. XRD tests5for alloy and thin films showed that polycrystalline5and have the tetragonal structure with preferential5orientation in the [112] direction respectively. C. The influence of annealing5on the values of optical parameters of AgInSe2 thin5films is investigated. All thin films exhibited5allowed direct optical5energy band gap and high absorption in the visible region, thus, making the films suitable5for optoelectronic devices, for instance as window layers of solar cells. D.The electrical5conductivity and activation energies of AIS films are seen to be dependent5on the film annealing, the electrical conductivity5shows as an increase of behavior5with an increase of annealing. The resistivity5of these films are small. Hall effect5measurements confirmed that electrons were predominating5in the conduction process. Both5the mobility and concentration5of the charge carriers increase5 with the increase of annealing. References [1]. 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(2002). [17]. Kenji Yoshino, Aya Kinoshita, Yasuhiro Hirakata, Minoru Oshima Keita Nomoto, Tsuyoshi Yoshitake , Shunji Ozaki and Tetsuo Ikari., Structural and electrical characterization of AgInSe2 crystals grown by hot-press method, Journal of Physics: Conference Series 100 042042 ,pp1-4.( 2008). [18]. R.D. Tomlinson; A.E. Hill, and R.D. Pilkington, Ternary and Multinary Compounds, Proceedings of the 11th International Conference, University of Salford, 8-12 September, (1997). [19]. S. Murugana, and K.R. Muralib, Structural, Optical, and Electrical Studies on Pulse Plated AgInSe2 Films ACTA PHYSICA POLONICA A , 126,. 3, (2014).