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Structural and optical properties of gadolinium doped ZnTe thin films
Journal Pre-proofs Structural and optical properties of gadolinium doped ZnTe thin films J.D. López, L. Tirado-Mejía, H. Ariza-Calderón, H. Riascos, F. de Anda, E. Mosquera PII: DOI: Reference:
S0167-577X(20)30267-6 https://doi.org/10.1016/j.matlet.2020.127562 MLBLUE 127562
To appear in:
Materials Letters
Received Date: Accepted Date:
2 December 2019 23 February 2020
Please cite this article as: J.D. López, L. Tirado-Mejía, H. Ariza-Calderón, H. Riascos, F. de Anda, E. Mosquera, Structural and optical properties of gadolinium doped ZnTe thin films, Materials Letters (2020), doi: https://doi.org/ 10.1016/j.matlet.2020.127562
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier B.V.
Structural and optical properties of gadolinium doped ZnTe thin films J. D. López1, 2,*, L. Tirado-Mejía1, H. Ariza-Calderón1, H. Riascos3, F. de Anda4, E. Mosquera2, 5 1
Laboratorio de Optoelectrónica, Instituto Interdisciplinario de las Ciencias, Universidad del Quindío,
A.A. 460, Colombia. 2
Departamento de Física, Universidad del Valle, A.A. 25360, Cali, Colombia
3
Universidad Tecnológica de Pereira, Cra. 27 No 10-02, Pereira 660003, Risaralda, Colombia
4
Instituto de Investigación en Comunicación Óptica, UASLP, Av. Karakorum 1470, 78210 San Luis
Potosí, México 5
Centro de Excelencia en Nuevos Materiales, CENM, Universidad del Valle, A.A. 25360, Cali, Colombia
*Corresponding
author. Tel. (+57) 3127608894; E-mail: [email protected] ABSTRACT
ZnTe and Ga-doped ZnTe thin films were prepared onto glass and Te-doped GaSb substrates by thermal evaporation method under vacuum and their structural and optical properties were studied. XRD results show that for both substrates, the doping with gadolinium yield a reduction in the ZnTe lattice parameter. The optical band gap increases with incorporation of Gd into the ZnTe structure and the values obtained are 2.19 and 2.29 eV, respectively for glass and GaSb:Te substrates. The presence of defects due to Gd doping into ZnTe thin films is evidenced. Keywords: ZnTe; Thermal evaporation; Te-doped GaSb substrate; Thin films.
1. Introduction Zinc Telluride (ZnTe) is one of the II-VI most attractive chalcogenides semiconductors employed for the development of optoelectronic devices such as blue light emitting diodes, solar cells and radiation detection [1-3]. ZnTe is usually a p-type semiconductor, with a direct band gap of 2.26 eV ( 548 nm) at 300 K and a lattice constant of 6.103 Å [4]. Several methods have been developed for the preparation of ZnTe films such as liquid phase epitaxy (LPE), molecular beam epitaxy (MBE), thermal vapor deposition and pulsed laser deposition (PLD) [5-8]. With these methods, the choice of a substrate plays an important role in the deposition process, in particular for semiconductor diodes applications. Both ZnTe and Te-doped GaSb (GaSb:Te) with band gap of 0.814 eV at 11 K [9] have lattice constants close to 6.1 Å with a mismatch of only 0.13 %. Also, the large difference in their refractive index leads an excellent optical confinement of
the guided optical modes in semiconductor laser and others applications [10]. Therefore, several researchers have studied their structural, optical and electrical properties of In, Cu, Cr and Cd doped ZnTe films [11, 12]. However, the structural and optical properties of thermal evaporated Gd-doped ZnTe (ZnTe:Gd) thin films has not been reported. Thus, in this work, we present a study on structural and optical properties of thermally vacuum evaporate ZnTe and ZnTe:Gd thin films deposited onto glass and GaSb:Te substrates with potential application for medical and defense devices.
2. Experimental For the ZnTe films, glass slides and GaSb:Te single crystal were used as substrates. Initially, glass substrates (7.62 × 2.54 × 0.1 cm3) were clean with a soap solution and rinsed with distilled water; after that, the substrates were submitted to ultrasonic agitation for 30 min in order to remove residual impurities. They were cleaned in boiling methanol, boiling acetone and isopropyl alcohol at room temperature (RT) for 10 min and dried with nitrogen. In the other hand, the preparation of GaSb:Te substrates were carried out by chemical etching performed with a H2O2 (3.5 mL):HF(125 μL):C4O6H6(7.5 mL):H2O(2.35 mL) solution [13] during 5 min and then, the substrates were cleaned in boiling methanol, boiling acetone and isopropyl alcohol at RT for 10 min and dried with nitrogen. ZnTe and ZnTe:Gd thin films were prepared using a vacuum coating unit: 12" × 18" Pyrex Glass Bell Jar, rotary vane vacuum (Alcatel Pascal 2005 SD) for pre-vacuum, turbo-molecular high vacuum (Adixen Alcatel ATP), a current source, and a mechanical shutter. High purity powder of ZnTe (99,99 %) and chips of Gd (99,9 %) were used. The source-substrate distance was maintained at 13 cm and a rotary drive was employed to maintain uniformity in film thickness. The ZnTe (101 mg) powder were placed into a tantalum boat and it was heated indirectly by passing current through the electrodes. The procedure was carried out in vacuum under 10-5 mbar. The ZnTe:Gd films were prepared using the same technique employing as source a mixture of ZnTe (190 mg) and Gd (8.79 mg). Structural characterization of samples was carried out using a D8 Advance X-ray diffractometer (BRUKER, CuKα, λ = 0.154 nm) over a range of 2θ angle from 20° to 70° (step of 0.02°). The optical properties were measured by using a ChromTech CT8600 UV-vis-NIR spectrophotometer, in the wavelength range of 200 to 1100 nm. The morphological characterization was made using a SEM microscope (JEOLTM JSM 6490LV) coupled with energy dispersive spectroscopy (EDS). The films thickness was calculated from transmittance data using the point-wise unconstrained minimization approach (PUMA) method [14].
3. Results and discussion Fig. 1S shows the X-ray diffractograms of ZnTe and ZnTe:Gd thin films. The comparison between these diffractograms and ZnTe diffraction pattern suggests that Gd-doped samples have a cubic ZnTe structure and Gd atoms are incorporated into the ZnTe host. The 2θ peak observed around 25.35° corresponds to the
crystalline plane (111) [3]. The full width half maximum (FWHM) of the diffraction peaks at 25.18° and 25.40° increases with the Gd incorporation and with the substrate nature, being higher for glass substrate than for single crystal Te-doped GaSb substrate. Additionally, there is a peak shift towards higher diffraction angles for both Gd-doped samples, which suggests that the lattice parameter calculated through Rietveld refinement [15] is slightly lower (see Fig. 1(c) and Table 1). Our result is in agreement with those reported by Ma et. al., [16] confirming the anomalous behavior of lattice parameter with the incorporation of large impurity atom: Gd has bigger atomic radius (1.80 Å) than Zn (1.35 Å) and Te (1.40 Å). Therefore, for ZnTe an increase in the lattice parameter with the Gd incorporation may be expected. Also, this behavior can be understood by the presence of defect involving substitutional Gd ions and neighboring vacancies [16]. Using the Debye Scherrer equation, D = k / cos , the crystallite size has been estimated for the reflection from the (111) plane. The crystallite size values are reported in Table 1. It is observed that the crystallite size of polycrystalline films decreases with the increasing of Gd contents and with the substrate nature. Fig. 2S shows SEM micrographs for all of the as-deposited vacuum evaporated ZnTe thin film. The compositional analysis of the films obtained by EDS is presented in Table 1S. Here, we observed that (i) tellurium atoms were replaced by Gd atoms and (ii) the surfaces of the films have excess of tellurium due the segregation of Te [19]. On the other hand, optical spectra were measured in two different modes according to the substrate nature. For ZnTe films grown on glass substrates, we measured in transmission mode obtaining the absorption spectra; meanwhile, for samples grown on Te-doped GaSb substrates, it was necessary to use the reflectance mode. Therefore, from absorption spectra the optical band gap was determined using the Taucs’s equation,
hv = k(hv – Eg)n [17], where k is a constant, is the absorption coefficient, and n is equal to ½ or 2 for a direct or indirect band gap semiconductor, respectively. From reflectance (R) data, the optical band gap was determined using the Kubelka-Munk (K-M) function, F(R) = (1 – R)2(2R)–1 [18]. The optical band gap of the ZnTe/Glass, ZnTe:Gd/Glass, ZnTe/GaSb, and ZnTe:Gd/GaSb films calculated are reported in Table 1 and Fig. 2. The lower values of 2.12 eV and 2.17 eV for ZnTe/GaSb and ZnTe:Ga/GaSb films, respectively, compared to the value of 2.26 eV reported for ZnTe, may be attributed to disorder and imperfections into the monocrystalline Te-doped GaSb substrate. The change in the optical band gap of Gd-doped ZnTe films has been previously reported by Ma et. al., [16]. Instead, for as-deposited ZnTe films on glass substrate the optical band gap increase with Gd incorporation presenting a blue shift (E = 0.02 eV) with respect to pure ZnTe.
4. Conclusion Gd-doped ZnTe thin films were deposited by thermal evaporation method at room temperature onto glass substrates and chemical etched Te-GaSb single crystal. XRD of the samples showed that the films are
polycrystalline and have a cubic ZnTe structure. Also, it was observed that the crystallite size and lattice parameter decrease with Gd doping. In addition, the optical band gap of these films is found to be lower for Te-GaSb substrate that for glass substrate. Moreover, the optical band gap of the ZnTe:Gd/Glass is slightly blue shift compared with ZnTe/Glass thin films. Acknowledgements This research has been supported by the University of Quindío, Colombia. References [1] Pandey N., Kumar B., Dwivedi D.K. Mater. Res. Express, 6(9), 2019, 096425. DOI: 10.1088/20531591/ab2fb8. [2] Mikhailik V., Galkin S., Rudko M., Gamernyk R., Hrytsak A., Kapustianyk V., Kraus H., Panasiuk M., Rudyk V. J. Physical Studies, 21(4), 2017, 4201-1-4201-5. [3] Mosquera E. Mater. Express. 9(2), 2019, 173-178. DOI: 10.1166/mex.2019.1480. [4] Ibrahim A. A., El-Sayed N. Z., Kaid M. A., Ashour A. Vacuum, 75, 2004, 189. DOI: 10.1016/j.vacuum.2004.02.005 [5] Widmer R., Bortfeld D. P., Kleinknecht H. P. J. Cryst. Growth. 6, 1970, 237. DOI: 10.1016/00220248(70)90072-2 [6] Nakasu T., Aiba T., Yamashita S., Hattori S., Sun W., Taguri K., Kazami F., Kobayashi M., Asahi T. J. Cryst. Growth, 425, 2015, 191. DOI: 10.1016/j.jcrysgro.2015.02.052 [7] Amutha, R. Adv. Mat. Lett. 4, 2013, 225. DOI: 10.5185/amlett.2012.7387 [8] Ghosh B., Ghosh D., Hussain S., Bhar R., Pal A. K. J. Alloys Compd. 541, 2012, 104. DOI: 10.1016/j.jallcom.2012.06.063 [9] Tirado-Mejía L., Villada J. A., de los Ríos M., Peñafiel J. A., Fonthal G., Espinosa-Arbelaéz D. G., Ariza-Calderón H., Rodríguez-García M. E. Phys. B. 403, 2008, 4027. DOI: 10.1016/j.physb.2008.07.049 [10] Kamuro S., Hamaguchi C., Fukushima M., Nakai J. Solid-State Electron. 14, 1971, 1183. DOI: 10.1016/0038-1101(71)90106-7 [11] Gul Q., Zakria M., Khan T. M., Mahmood A., Iqbal A. Mater. Sci. Semicond. Process.19, 2014, 17. DOI: 10.1016/j.mssp.2013.11.033 [12] Sharma D. C., Srivastava S., Vijay Y. K., Sharma Y. K. Adv. Mat. Lett. 4, 2013, 68. DOI: 10.5185/amlett.2013.icnano.118 [13] Berishev I. E., De Anda F., Mishournyi V. A., Olvera J. N., Ilyinskaya D., Vasilyev V. I. J. Electrochem. Soc.142, 1995, L189. DOI: 10.1002/chin.199604290
[14] Birgin E. G., Chambouleyron I., Martínez J. M. J. Comput. Phys.151, 1999, 862. DOI: 10.1006/jcph.1999.6224 [15] Rietveld H. M. J. Appl. Crystallogr. 2, 1969, 65–71. DOI: 10.1107/S0021889869006558 [16] Ma Z., Liu L., Yu K. M., Walukiewicz W., Perry D. L., Yu P. Y., Mao S. S. J. Appl. Phys. 103, 2008, 023711. DOI: 10.1063/1.2832403 [17] Tauc J., Grigorovici R., Vancu A. Phys. Stat. Sol. 15, 1966, 627. DOI: 10.1002/pssb.19660150224 [18] Kubelka P., Munk F. Z. Tech. Phys. 12, 1931, 593. [19] P.S. Dutta, A.G. Ostrogorsky, J. Crys. Growth, Vol. 197, Iss. 4, 1999, Pag. 749-754. DOI: 10.1016/S0022-0248(98)00976-2
Figure and Table captions Figure 1. XRD of the (111) plane for ZnTe and ZnTe:Gd deposited onto (a) glass substrates and (b) TeGaSb substrates. (c) Band gap vs lattice parameter of the thin films. Figure 2. Optical band gap spectra of (a) ZnTe/GaSb (b) ZnTe:Gd/GaSb (c) ZnTe /Glass and (d) ZnTe:Gd/Glass thin films. Table 1. Calculated crystallite size, lattice parameter and band gap for ZnTe and Gd-doped ZnTe evaporated films.
Sample
(hkl)
ZnTe/Glass ZnTe:Gd/Glass ZnTe/GaSb ZnTe:Gd/GaSb
(111)
Crystallite size (nm) 19.98
Lattice parameter (Å) 6.607
Band gap (eV) 2.27
14.12
6.604
2.29
28.30
6.121
2.12
27.28
6.092
2.17
Figures Figure 1.
Figure 2.
CRediT author statement Jeison D. López: Conceptualization, Methodology, Software, Validation, Investigation, Visualization, Writing – Original Draft. L. Tirado-Mejía: Conceptualization, Methodology, Supervision, Investigation, Resources, Writing – Review & Editing. E. Mosquera: Conceptualization, Supervision, Writing – Review & Editing. H. Ariza-Calderón: Methodology, Supervision. H. Riascos: Methodology, Supervision. F. de Anda: Methodology, Supervision. Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Research Highlight The optical band gap is slightly blue shift with Gd incorporation. The crystallite size and lattice parameter decrease with Gd doping. The presence of defects due to Gd doping into ZnTe thin films is evidenced.
S0167-577X(20)30267-6 https://doi.org/10.1016/j.matlet.2020.127562 MLBLUE 127562
To appear in:
Materials Letters
Received Date: Accepted Date:
2 December 2019 23 February 2020
Please cite this article as: J.D. López, L. Tirado-Mejía, H. Ariza-Calderón, H. Riascos, F. de Anda, E. Mosquera, Structural and optical properties of gadolinium doped ZnTe thin films, Materials Letters (2020), doi: https://doi.org/ 10.1016/j.matlet.2020.127562
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier B.V.
Structural and optical properties of gadolinium doped ZnTe thin films J. D. López1, 2,*, L. Tirado-Mejía1, H. Ariza-Calderón1, H. Riascos3, F. de Anda4, E. Mosquera2, 5 1
Laboratorio de Optoelectrónica, Instituto Interdisciplinario de las Ciencias, Universidad del Quindío,
A.A. 460, Colombia. 2
Departamento de Física, Universidad del Valle, A.A. 25360, Cali, Colombia
3
Universidad Tecnológica de Pereira, Cra. 27 No 10-02, Pereira 660003, Risaralda, Colombia
4
Instituto de Investigación en Comunicación Óptica, UASLP, Av. Karakorum 1470, 78210 San Luis
Potosí, México 5
Centro de Excelencia en Nuevos Materiales, CENM, Universidad del Valle, A.A. 25360, Cali, Colombia
*Corresponding
author. Tel. (+57) 3127608894; E-mail: [email protected] ABSTRACT
ZnTe and Ga-doped ZnTe thin films were prepared onto glass and Te-doped GaSb substrates by thermal evaporation method under vacuum and their structural and optical properties were studied. XRD results show that for both substrates, the doping with gadolinium yield a reduction in the ZnTe lattice parameter. The optical band gap increases with incorporation of Gd into the ZnTe structure and the values obtained are 2.19 and 2.29 eV, respectively for glass and GaSb:Te substrates. The presence of defects due to Gd doping into ZnTe thin films is evidenced. Keywords: ZnTe; Thermal evaporation; Te-doped GaSb substrate; Thin films.
1. Introduction Zinc Telluride (ZnTe) is one of the II-VI most attractive chalcogenides semiconductors employed for the development of optoelectronic devices such as blue light emitting diodes, solar cells and radiation detection [1-3]. ZnTe is usually a p-type semiconductor, with a direct band gap of 2.26 eV ( 548 nm) at 300 K and a lattice constant of 6.103 Å [4]. Several methods have been developed for the preparation of ZnTe films such as liquid phase epitaxy (LPE), molecular beam epitaxy (MBE), thermal vapor deposition and pulsed laser deposition (PLD) [5-8]. With these methods, the choice of a substrate plays an important role in the deposition process, in particular for semiconductor diodes applications. Both ZnTe and Te-doped GaSb (GaSb:Te) with band gap of 0.814 eV at 11 K [9] have lattice constants close to 6.1 Å with a mismatch of only 0.13 %. Also, the large difference in their refractive index leads an excellent optical confinement of
the guided optical modes in semiconductor laser and others applications [10]. Therefore, several researchers have studied their structural, optical and electrical properties of In, Cu, Cr and Cd doped ZnTe films [11, 12]. However, the structural and optical properties of thermal evaporated Gd-doped ZnTe (ZnTe:Gd) thin films has not been reported. Thus, in this work, we present a study on structural and optical properties of thermally vacuum evaporate ZnTe and ZnTe:Gd thin films deposited onto glass and GaSb:Te substrates with potential application for medical and defense devices.
2. Experimental For the ZnTe films, glass slides and GaSb:Te single crystal were used as substrates. Initially, glass substrates (7.62 × 2.54 × 0.1 cm3) were clean with a soap solution and rinsed with distilled water; after that, the substrates were submitted to ultrasonic agitation for 30 min in order to remove residual impurities. They were cleaned in boiling methanol, boiling acetone and isopropyl alcohol at room temperature (RT) for 10 min and dried with nitrogen. In the other hand, the preparation of GaSb:Te substrates were carried out by chemical etching performed with a H2O2 (3.5 mL):HF(125 μL):C4O6H6(7.5 mL):H2O(2.35 mL) solution [13] during 5 min and then, the substrates were cleaned in boiling methanol, boiling acetone and isopropyl alcohol at RT for 10 min and dried with nitrogen. ZnTe and ZnTe:Gd thin films were prepared using a vacuum coating unit: 12" × 18" Pyrex Glass Bell Jar, rotary vane vacuum (Alcatel Pascal 2005 SD) for pre-vacuum, turbo-molecular high vacuum (Adixen Alcatel ATP), a current source, and a mechanical shutter. High purity powder of ZnTe (99,99 %) and chips of Gd (99,9 %) were used. The source-substrate distance was maintained at 13 cm and a rotary drive was employed to maintain uniformity in film thickness. The ZnTe (101 mg) powder were placed into a tantalum boat and it was heated indirectly by passing current through the electrodes. The procedure was carried out in vacuum under 10-5 mbar. The ZnTe:Gd films were prepared using the same technique employing as source a mixture of ZnTe (190 mg) and Gd (8.79 mg). Structural characterization of samples was carried out using a D8 Advance X-ray diffractometer (BRUKER, CuKα, λ = 0.154 nm) over a range of 2θ angle from 20° to 70° (step of 0.02°). The optical properties were measured by using a ChromTech CT8600 UV-vis-NIR spectrophotometer, in the wavelength range of 200 to 1100 nm. The morphological characterization was made using a SEM microscope (JEOLTM JSM 6490LV) coupled with energy dispersive spectroscopy (EDS). The films thickness was calculated from transmittance data using the point-wise unconstrained minimization approach (PUMA) method [14].
3. Results and discussion Fig. 1S shows the X-ray diffractograms of ZnTe and ZnTe:Gd thin films. The comparison between these diffractograms and ZnTe diffraction pattern suggests that Gd-doped samples have a cubic ZnTe structure and Gd atoms are incorporated into the ZnTe host. The 2θ peak observed around 25.35° corresponds to the
crystalline plane (111) [3]. The full width half maximum (FWHM) of the diffraction peaks at 25.18° and 25.40° increases with the Gd incorporation and with the substrate nature, being higher for glass substrate than for single crystal Te-doped GaSb substrate. Additionally, there is a peak shift towards higher diffraction angles for both Gd-doped samples, which suggests that the lattice parameter calculated through Rietveld refinement [15] is slightly lower (see Fig. 1(c) and Table 1). Our result is in agreement with those reported by Ma et. al., [16] confirming the anomalous behavior of lattice parameter with the incorporation of large impurity atom: Gd has bigger atomic radius (1.80 Å) than Zn (1.35 Å) and Te (1.40 Å). Therefore, for ZnTe an increase in the lattice parameter with the Gd incorporation may be expected. Also, this behavior can be understood by the presence of defect involving substitutional Gd ions and neighboring vacancies [16]. Using the Debye Scherrer equation, D = k / cos , the crystallite size has been estimated for the reflection from the (111) plane. The crystallite size values are reported in Table 1. It is observed that the crystallite size of polycrystalline films decreases with the increasing of Gd contents and with the substrate nature. Fig. 2S shows SEM micrographs for all of the as-deposited vacuum evaporated ZnTe thin film. The compositional analysis of the films obtained by EDS is presented in Table 1S. Here, we observed that (i) tellurium atoms were replaced by Gd atoms and (ii) the surfaces of the films have excess of tellurium due the segregation of Te [19]. On the other hand, optical spectra were measured in two different modes according to the substrate nature. For ZnTe films grown on glass substrates, we measured in transmission mode obtaining the absorption spectra; meanwhile, for samples grown on Te-doped GaSb substrates, it was necessary to use the reflectance mode. Therefore, from absorption spectra the optical band gap was determined using the Taucs’s equation,
hv = k(hv – Eg)n [17], where k is a constant, is the absorption coefficient, and n is equal to ½ or 2 for a direct or indirect band gap semiconductor, respectively. From reflectance (R) data, the optical band gap was determined using the Kubelka-Munk (K-M) function, F(R) = (1 – R)2(2R)–1 [18]. The optical band gap of the ZnTe/Glass, ZnTe:Gd/Glass, ZnTe/GaSb, and ZnTe:Gd/GaSb films calculated are reported in Table 1 and Fig. 2. The lower values of 2.12 eV and 2.17 eV for ZnTe/GaSb and ZnTe:Ga/GaSb films, respectively, compared to the value of 2.26 eV reported for ZnTe, may be attributed to disorder and imperfections into the monocrystalline Te-doped GaSb substrate. The change in the optical band gap of Gd-doped ZnTe films has been previously reported by Ma et. al., [16]. Instead, for as-deposited ZnTe films on glass substrate the optical band gap increase with Gd incorporation presenting a blue shift (E = 0.02 eV) with respect to pure ZnTe.
4. Conclusion Gd-doped ZnTe thin films were deposited by thermal evaporation method at room temperature onto glass substrates and chemical etched Te-GaSb single crystal. XRD of the samples showed that the films are
polycrystalline and have a cubic ZnTe structure. Also, it was observed that the crystallite size and lattice parameter decrease with Gd doping. In addition, the optical band gap of these films is found to be lower for Te-GaSb substrate that for glass substrate. Moreover, the optical band gap of the ZnTe:Gd/Glass is slightly blue shift compared with ZnTe/Glass thin films. Acknowledgements This research has been supported by the University of Quindío, Colombia. References [1] Pandey N., Kumar B., Dwivedi D.K. Mater. Res. Express, 6(9), 2019, 096425. DOI: 10.1088/20531591/ab2fb8. [2] Mikhailik V., Galkin S., Rudko M., Gamernyk R., Hrytsak A., Kapustianyk V., Kraus H., Panasiuk M., Rudyk V. J. Physical Studies, 21(4), 2017, 4201-1-4201-5. [3] Mosquera E. Mater. Express. 9(2), 2019, 173-178. DOI: 10.1166/mex.2019.1480. [4] Ibrahim A. A., El-Sayed N. Z., Kaid M. A., Ashour A. Vacuum, 75, 2004, 189. DOI: 10.1016/j.vacuum.2004.02.005 [5] Widmer R., Bortfeld D. P., Kleinknecht H. P. J. Cryst. Growth. 6, 1970, 237. DOI: 10.1016/00220248(70)90072-2 [6] Nakasu T., Aiba T., Yamashita S., Hattori S., Sun W., Taguri K., Kazami F., Kobayashi M., Asahi T. J. Cryst. Growth, 425, 2015, 191. DOI: 10.1016/j.jcrysgro.2015.02.052 [7] Amutha, R. Adv. Mat. Lett. 4, 2013, 225. DOI: 10.5185/amlett.2012.7387 [8] Ghosh B., Ghosh D., Hussain S., Bhar R., Pal A. K. J. Alloys Compd. 541, 2012, 104. DOI: 10.1016/j.jallcom.2012.06.063 [9] Tirado-Mejía L., Villada J. A., de los Ríos M., Peñafiel J. A., Fonthal G., Espinosa-Arbelaéz D. G., Ariza-Calderón H., Rodríguez-García M. E. Phys. B. 403, 2008, 4027. DOI: 10.1016/j.physb.2008.07.049 [10] Kamuro S., Hamaguchi C., Fukushima M., Nakai J. Solid-State Electron. 14, 1971, 1183. DOI: 10.1016/0038-1101(71)90106-7 [11] Gul Q., Zakria M., Khan T. M., Mahmood A., Iqbal A. Mater. Sci. Semicond. Process.19, 2014, 17. DOI: 10.1016/j.mssp.2013.11.033 [12] Sharma D. C., Srivastava S., Vijay Y. K., Sharma Y. K. Adv. Mat. Lett. 4, 2013, 68. DOI: 10.5185/amlett.2013.icnano.118 [13] Berishev I. E., De Anda F., Mishournyi V. A., Olvera J. N., Ilyinskaya D., Vasilyev V. I. J. Electrochem. Soc.142, 1995, L189. DOI: 10.1002/chin.199604290
[14] Birgin E. G., Chambouleyron I., Martínez J. M. J. Comput. Phys.151, 1999, 862. DOI: 10.1006/jcph.1999.6224 [15] Rietveld H. M. J. Appl. Crystallogr. 2, 1969, 65–71. DOI: 10.1107/S0021889869006558 [16] Ma Z., Liu L., Yu K. M., Walukiewicz W., Perry D. L., Yu P. Y., Mao S. S. J. Appl. Phys. 103, 2008, 023711. DOI: 10.1063/1.2832403 [17] Tauc J., Grigorovici R., Vancu A. Phys. Stat. Sol. 15, 1966, 627. DOI: 10.1002/pssb.19660150224 [18] Kubelka P., Munk F. Z. Tech. Phys. 12, 1931, 593. [19] P.S. Dutta, A.G. Ostrogorsky, J. Crys. Growth, Vol. 197, Iss. 4, 1999, Pag. 749-754. DOI: 10.1016/S0022-0248(98)00976-2
Figure and Table captions Figure 1. XRD of the (111) plane for ZnTe and ZnTe:Gd deposited onto (a) glass substrates and (b) TeGaSb substrates. (c) Band gap vs lattice parameter of the thin films. Figure 2. Optical band gap spectra of (a) ZnTe/GaSb (b) ZnTe:Gd/GaSb (c) ZnTe /Glass and (d) ZnTe:Gd/Glass thin films. Table 1. Calculated crystallite size, lattice parameter and band gap for ZnTe and Gd-doped ZnTe evaporated films.
Sample
(hkl)
ZnTe/Glass ZnTe:Gd/Glass ZnTe/GaSb ZnTe:Gd/GaSb
(111)
Crystallite size (nm) 19.98
Lattice parameter (Å) 6.607
Band gap (eV) 2.27
14.12
6.604
2.29
28.30
6.121
2.12
27.28
6.092
2.17
Figures Figure 1.
Figure 2.
CRediT author statement Jeison D. López: Conceptualization, Methodology, Software, Validation, Investigation, Visualization, Writing – Original Draft. L. Tirado-Mejía: Conceptualization, Methodology, Supervision, Investigation, Resources, Writing – Review & Editing. E. Mosquera: Conceptualization, Supervision, Writing – Review & Editing. H. Ariza-Calderón: Methodology, Supervision. H. Riascos: Methodology, Supervision. F. de Anda: Methodology, Supervision. Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Research Highlight The optical band gap is slightly blue shift with Gd incorporation. The crystallite size and lattice parameter decrease with Gd doping. The presence of defects due to Gd doping into ZnTe thin films is evidenced.