- Email: [email protected]
Growth and application of Sb0.5Mo0.5Se2 ternary alloy as photodetector
Materials Letters: X 2 (2019) 100013
Contents lists available at ScienceDirect
Materials Letters: X journal homepage: www.elsevier.com/locate/mlblux
Growth and application of Sb0.5Mo0.5Se2 ternary alloy as photodetector Vijay Dixit a,⇑, Payal Chauhan a, Alkesh B. Patel a, Som Narayan b, P.K. Jha b, G.K. Solanki a, K.D. Patel a,⇑, V.M. Pathak a a b
Department of Physics, Sardar Patel University, Vallabh Vidya Nagar, Anand 388120, Gujarat, India Department of Physics, The Maharaja Sayajirao University of Baroda, Vadodara 390002, Gujarat, India
a r t i c l e
i n f o
a b s t r a c t
Article history: Received 5 April 2019 Received in revised form 20 April 2019 Accepted 23 April 2019 Available online 23 April 2019
Presently, ternary alloy engineering holds ability in promoting high performance photo detecting devices. In the present investigation, we have employed direct vapor transport technique (DVT) to grow Sb0.5Mo0.5Se2 multilayer crystal for its use as photodetector. To confirm the composition of the grown crystals, energy dispersive analysis of x-ray (EDAX) is performed. To explore the morphological properties, optical microscopy and scanning electron microscopy (SEM) are used and the growth from vapor phase that is initiated due to screw dislocation is observed. The phase composition and optical properties of the as grown crystals are examined by transmission electron microscopy (TEM) and UV–Visible spectroscopy providing indirect energy band gap of 1.22 eV. Raman spectra of both pure MoSe2 and Sb0.5Mo0.5Se2 show the presence of the out of plane A1g vibrational mode at 243 cm1. In addition, to study photo conduction property, the mechanically exfoliated crystal was illuminated by polychromatic source having intensity of 50 mWcm2 at different bias voltages. Ó 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: DVT Crystal growth Sb0.5Mo0.5Se2 SEM SAED Raman Photo current Responsivity and detectivity
1. Introduction Electronic devices with quick response to light, fast switching capability and better performance are preferred for industrial and research sectors. There are numerous materials possessing the photo-sensing properties such as black phosphorous, graphene, graphene oxide and transition metal dichalcogenides (TMDCs). Properties such as flexibility in synthesis, mobility, environmental stability, carrier concentration, structural, vibrational and highly crystalline nature have made TMDCs the most fascinating material [1–8]. Recently, the photo-sensing properties and energy band gap of TMDCs material were altered for achieving high photoresponsivity and detectivity by alloy engineering [9]. The semiconducting layered TMDCs are in great demand due to their robust material properties and as quick switching photosensors [10]. TMDCs have also shown great potential in its use as photo sensors, field effect transistors (FET), humidity sensors, gas sensors, touch less positioning systems and many more as optoelectronic, photonic and photovoltaic devices [11–14]. Within the TMDCs family, MoS2 and MoSe2 materials are widely investigated due to their excellent photo conducting properties. The highly oriented and crystalline
⇑ Corresponding authors. E-mail addresses: (K.D. Patel).
[email protected]
(V.
Dixit),
[email protected]
TMDCs are composed of stacks of MX2 tri-layers along c-axis [15]. Alloy engineering (i.e. doping) has great deal of influence over the performance of the photo detector. The quick response of the photo detector was achieved by alloying vanadium and antimony in SnSe2 material [9,16]. This became the sole reason to grow Sb0.5Mo0.5Se2 single crystals by DVT technique concerning vapor transport crystal growth [17]. Then, the morphological, structural, optical and vibrational properties of the grown crystals were studied. The photoconduction property of mechanically exfoliated crystal along the basal plane is studied under polychromatic source of intensity 50 mWcm2 and its other photo-sensing parameters are reported here in detail. 2. Experimental In the present investigation to grow single crystals of Sb0.5Mo0.5Se2, constituent material such as antimony (Sb), molybdenum (Mo), and selenium (Se) all 99.99% pure are procured from Alfa Aesar. These materials are mixed in stoichiometric proportion weighing 10 g and placed in a clean dry quartz ampoule of dimensions 250 mm long, 25 mm outer diameter and 22 mm inner diameter and sealed at a pressure 105 torr. Afterwards, the sealed ampoule is loaded in a temperature controlled dual zone horizontal furnace. The temperatures at the two zones i.e. source zone and growth zone are increased at the rate of 24 K/h till they reach
https://doi.org/10.1016/j.mlblux.2019.100013 2590-1508/Ó 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
2
V. Dixit et al. / Materials Letters: X 2 (2019) 100013
1353 K and 1323 K at the two zones. These temperatures are held constant for another 99 h and, then, the temperatures at the source zone and growth zone are reduced to room temperature by the rate of 12 K/h. After growth cycle completion, the ampoule is removed from the furnace, and bigger size shining crystals are observed in the ampoule having dimensions of 6 mm 4 mm and an average thickness of 35–40 lm. To check the grown crystal purity, EDAX is carried out by Phillips FESEM XL 30, (see supplementary material, Fig. 1). The EDAX analysis confirms the absence of foreign elements and the nearly stoichiometric constituent element contents in w/t%, Mo(14.35%), Sb(20.12%) and Se(65.53%). The morphological and structural properties of as grown crystals are examined by optical microscope, scanning electron microscope (SEM) and selected area electron diffraction (SAED). To evaluate their optical and vibrational properties, UV–Visible spectroscopy (Perkin Elmer Lambda 19) and Raman spectroscopy (STR 500, 532 nm excitation) were employed. To study the photo-conduction properties of the exfoliated sample, we have adopted the method presented elsewhere [18].
3. Result and discussion The surface topographic properties give direct insight of defects associated with crystal growth. The surface images of as grown crystal examined under an optical microscope (OM) is shown in
Fig. 1(a–b). In Fig. 1(a), the clean and flat surface suitable for photovoltaic and optoelectronic device applications is seen, and, in Fig. 1(b), the presence of helical spirals, confirming the crystal growth initiated from screw dislocation defect is evident [9,16]. We have presented the SEM images showing randomly oriented micron sized hexagonal shaped crystals possessing layered structure (see supplementary material, Fig. 2). The results obtained from SEM and OM analysis confirms the layered growth mechanism. To define the phase composition, a tiny crystal is ultrasonically exfoliated in acetone and its selected area electron diffraction (SAED) pattern was recorded by 200 kV TEM, as shown in Fig. 1(c). The spot like pattern is arranged in a hexagonal type pattern confirming single crystalline phase and hexagonal structure of the as grown crystal [5,16,19]. To explore the optical properties of the as grown crystal, the UV–Visible spectroscopy in the range of 600–1000 nm is performed and a sharp absorbance edge in the spectral range of 825–900 nm is observed, as displayed in Fig. 1(d). To determine the energy band gap we are presenting the plot of indirect allowed transition (ahm)1/2 versus photon energy (hm) displayed in Fig. 1(e). The extrapolation of the linear portion of the graph to fundamental absorption edge gives indirect energy band gap of 1.22 eV. One can observe few discontinuities in the Tauc plot (see supplementary material, Fig. 3a), and it may take place due to inter band transition of absorption and emission of phonons. We have adopted method presented elsewhere for making specific measurement at the point of discontinuities E1,E2, E3
Fig. 1. (a) Optical micrograph showing flat surface (b) screw dislocation (c) Electron diffraction pattern (d) absorption spectra (e) indirect energy band gap (f) Raman spectra.
3
V. Dixit et al. / Materials Letters: X 2 (2019) 100013
Fig. 2. (a) Pulse photo response of Sb0.5Mo0.5Se2 crystal recorded under a polychromatic source of intensity 50 mWcm2 (b) Single pulse response.
Table 1 Parameters of photo response of Sb0.5Mo0.5Se2 crystal compared with previous report. Material
Voltage (V)
Iph (lA)
Rk (lAW1)
D* 107 (Jones)
Tr (s)
Td (s)
References
Sb0.5Mo0.5Se2
1.00 2.00 3.00 0.30 –
4.34 8.39 11.48 1.88 0.02
543.00 1049.00 1435.00 – –
0.20 0.27 0.29 – –
0.97 0.97 0.97 4.40 3
1.00 1.00 1.00 4.50 3
This work
Sb0.1Sn0.9Se2 SnSe
and E4 [5,18]. These points are related to beginning of absorption of first phonon, second phonon and emission of second and first phonon. These four energies corresponds exactly to the non linear nature, the indirect energy band gap ‘‘Eg0 = (E1 + E4)/2 = (E2 + E3)/2” due to absorption and emission of phonon comes out to be 1.16 eV, similarly ‘‘Ep1 = (E4 E1)/2 and Ep2 = (E3 E2)/2” are the absorbed and emitted phonon energies that comes out to be 15 meV and 5 meV. The reciprocal of slope in plot of lna versus photon energy (see supplementary material, Fig. 3b) gives Urbach energy (Eu = 0.57 eV). The steepness constant ‘‘r = kBT/Eu” where kB is Boltzman constant and T is the room temperature, comes out to be 0.04. In Fig. 1(f), the Raman spectra of Sb0.5Mo0.5Se2 and MoSe2 are comparatively shown, and one can evince the presence of out of plane A1g mode in both samples at 243.55 cm1 and 243.60 cm1. A slight shift in the peak position of doped sample confirms the substitution of Sb (ionic radius 74 pm) for Mo (ionic radius 79 pm) and thus preserving the 2H-polytype of the grown crystal [16,20]. To explore the photo-conducting properties of mechanically exfoliated crystal, Keithley 2400 SMU is employed to record current versus time plot at different bias voltage and under a polychromatic source of intensity 50 mWcm2 by periodically on/off switching source. In Fig. 2(a–b), the repeatable and single pulse photo responses of cleaved crystal are given. It can be evinced from Fig. 2(a–b) that current rises quickly (rise time
[16] [14]
Tr) upon illumination (i.e. causing e-h pair generation) and, due to the presence of electric field, electrons get separated and contributes in photo-current. As the source is switched off, the photo-current decays slowly (decay time Td). It could possibly appear due to several factors. First, it could be due to mechanical exfoliation of crystal, Second, it could be due to defect states behaving as trapping centre for electrons (i.e. deep level defect states, DLDS) aroused at high temperature growth [21]. Third, as the entire experiment is carried out in an open atmosphere condition, it give a possibility of adsorption of oxygen present in the air to the surface (i.e. holding electron) and hence behaving as an additional trapping centre [9]. The photo detecting parameter such as responsivity is evaluated by (Rk = Iph/PS), where photo-current ‘‘Iph = Ion Idark”, ‘P’ is incident power and exposed area ‘S = 16 mm2’, detectivity (D* = RkS1/2/(2eIdark)1/2) [22] is presented in Table1.
4. Conclusion The single crystal of Sb0.5Mo0.5Se2 is grown by DVT technique. The chemical purity and stoichiometric proportion of constituent elements in grown crystal are confirmed by EDAX analysis. The micro morphology of as grown crystals investigated by optical
4
V. Dixit et al. / Materials Letters: X 2 (2019) 100013
microscope and SEM analysis confirms that the growth initiated at the screw dislocation defect. The structure and single crystal state verification are evidenced by electron diffraction studies. Raman spectroscopy confirms the presence of out of plane A1g vibrational mode and a slight shift in the peak position on doping confirms the substitution of Sb onto the Mo sites. The device shows quick switching action and fast response on illumination. The photocurrent, responsivity and detectivity are enhanced on increasing bias voltage from 1 to 3 V. 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. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.mlblux.2019.100013. References [1] W.H. Britton, O.H. Hugh, Churchill, Y. Yafang, J.H. Pablo, Nat. Nano 9 (2014) 262. [2] C.U. Vyas, P. Pataniya, C.K. Zankat, V.M. Pathak, K.D. Patel, G.K. Solanki, Mater. Sci. Semicond. Process. 71 (2017) 226.
[3] J. Yao, Z. Zheng, G. Yang, Appl. Mat. Int. 8 (2016) 12915. [4] H.T. Yuan, M.S. Bahramy, K. Morimoto, S.F. Wu, K. Nomura, B.J. Yang, H. Shimotani, R. Suzuki, M. Toh, C. Kloc, Nat. Phys. 9 (2013) 563. [5] A. Patel, P. Pataniya, S. Narayan, C.K. Sumesh, V.M. Pathak, G.K. Solanki, K.D. Patel, P.K. Jha, Mater. Sci. Semicond. Process 81 (2018) 108. [6] A.B. Patel, H.K. Machhi, P. Chauhan, S. Narayan, V. Dixit, S.S. Soni, P.K. Jha, G.K. Solanki, K.D. Patel, V.M. Pathak, A.C.S. App, Mater. Interfaces 11 (2019) 4093. [7] C.C. Hsiao, W.C. Lan, P. Jiang, C.M. Hui, P. Kumar, T. Taishi, 2D Mater. 1 (2014) 034001. [8] K.A. Kokh, V.V. Atuchin, T.A. Gavrilova, N.V. Kuratieva, N.V. Pervukhina, N.V. Surovtsev, Solid State Commun. 177 (2014) 16. [9] C.K. Zankat, P. Pataniya, M. Tannarana, G.K. Solanki, K.D. Patel, V.M. Pathak, Mater. Sci. Semicond. Process 91 (2019) 383. [10] C. Guo, Z. Tian, Y. Xiao, Q. Mi, J. Xue, Appl. Phys. Lett 109 (2016) 203104. [11] G.L. Frey, R. Tenne, J. Mater. Res. 13 (9) (1998) 2412. [12] W.J. Yu, Y. Liu, H. Zhou, A. Yin, Z. Li, Y. Huang, X. Duan, Nat. Nanotech. 8 (2013) 952. [13] A.K. Geim, I.V. Grigorieva, Nature 449 (2013) 419. [14] A.S. Pawbake, S.R. Jadkar, D.J. Late, Mater. Res. Express 3 (2016) 105038. [15] A.A. Tedstone, D.J. Lewis, P. O’brien, Chem. Mater 28 (2016) 1965. [16] M. Tannarana, P. Pataniya, G.K. Solanki, S.B. Pillai, K.D. Patel, P.K. Jha, V.M. Pathak, Appl. Surf. Sci 462 (2018) 856. [17] V.V. Atuchin, S.V. Borisov, T.A. Gavrilova, K.A. Kokh, N.V. Kuratieva, N.V. Pervukhina, Particuology 26 (2016) 118. [18] V. Dixit, S. Nair, J. Joy, C.U. Vyas, G.K. Solanki, K.D. Patel, V.M. Pathak, Mater. Sci. Semicond. Process 88 (2018) 1. [19] Y.M. Andreev, V.V. Atuchin, G.V. Lanskii, A.N. Morozov, L.D. Pokrovsky, S.Y. Sarkisov, O.V. Voevodina, Mater. Sci. Eng. B 128 (2006) 205. [20] Y. Liu, K. Tom, X. Zhang, S. Lou, Y. Liu, J. Yao, New J. Phys. 19 (2017) 073018. [21] M.A. Ghorbani, N.A. Enayshin, A. Kuc, G. Seifert, T. Henne, Phys. Rev. B: Condens. Matter Mater. Phys. 88 (24) (2013) 245540. [22] V. Dixit, C.U. Vyas, A.B. Patel, V.M. Pathak, G.K. Solanki, K.D. Patel, AIP Conf. Proc. 1961 (2018) 030017.
Contents lists available at ScienceDirect
Materials Letters: X journal homepage: www.elsevier.com/locate/mlblux
Growth and application of Sb0.5Mo0.5Se2 ternary alloy as photodetector Vijay Dixit a,⇑, Payal Chauhan a, Alkesh B. Patel a, Som Narayan b, P.K. Jha b, G.K. Solanki a, K.D. Patel a,⇑, V.M. Pathak a a b
Department of Physics, Sardar Patel University, Vallabh Vidya Nagar, Anand 388120, Gujarat, India Department of Physics, The Maharaja Sayajirao University of Baroda, Vadodara 390002, Gujarat, India
a r t i c l e
i n f o
a b s t r a c t
Article history: Received 5 April 2019 Received in revised form 20 April 2019 Accepted 23 April 2019 Available online 23 April 2019
Presently, ternary alloy engineering holds ability in promoting high performance photo detecting devices. In the present investigation, we have employed direct vapor transport technique (DVT) to grow Sb0.5Mo0.5Se2 multilayer crystal for its use as photodetector. To confirm the composition of the grown crystals, energy dispersive analysis of x-ray (EDAX) is performed. To explore the morphological properties, optical microscopy and scanning electron microscopy (SEM) are used and the growth from vapor phase that is initiated due to screw dislocation is observed. The phase composition and optical properties of the as grown crystals are examined by transmission electron microscopy (TEM) and UV–Visible spectroscopy providing indirect energy band gap of 1.22 eV. Raman spectra of both pure MoSe2 and Sb0.5Mo0.5Se2 show the presence of the out of plane A1g vibrational mode at 243 cm1. In addition, to study photo conduction property, the mechanically exfoliated crystal was illuminated by polychromatic source having intensity of 50 mWcm2 at different bias voltages. Ó 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: DVT Crystal growth Sb0.5Mo0.5Se2 SEM SAED Raman Photo current Responsivity and detectivity
1. Introduction Electronic devices with quick response to light, fast switching capability and better performance are preferred for industrial and research sectors. There are numerous materials possessing the photo-sensing properties such as black phosphorous, graphene, graphene oxide and transition metal dichalcogenides (TMDCs). Properties such as flexibility in synthesis, mobility, environmental stability, carrier concentration, structural, vibrational and highly crystalline nature have made TMDCs the most fascinating material [1–8]. Recently, the photo-sensing properties and energy band gap of TMDCs material were altered for achieving high photoresponsivity and detectivity by alloy engineering [9]. The semiconducting layered TMDCs are in great demand due to their robust material properties and as quick switching photosensors [10]. TMDCs have also shown great potential in its use as photo sensors, field effect transistors (FET), humidity sensors, gas sensors, touch less positioning systems and many more as optoelectronic, photonic and photovoltaic devices [11–14]. Within the TMDCs family, MoS2 and MoSe2 materials are widely investigated due to their excellent photo conducting properties. The highly oriented and crystalline
⇑ Corresponding authors. E-mail addresses: (K.D. Patel).
[email protected]
(V.
Dixit),
[email protected]
TMDCs are composed of stacks of MX2 tri-layers along c-axis [15]. Alloy engineering (i.e. doping) has great deal of influence over the performance of the photo detector. The quick response of the photo detector was achieved by alloying vanadium and antimony in SnSe2 material [9,16]. This became the sole reason to grow Sb0.5Mo0.5Se2 single crystals by DVT technique concerning vapor transport crystal growth [17]. Then, the morphological, structural, optical and vibrational properties of the grown crystals were studied. The photoconduction property of mechanically exfoliated crystal along the basal plane is studied under polychromatic source of intensity 50 mWcm2 and its other photo-sensing parameters are reported here in detail. 2. Experimental In the present investigation to grow single crystals of Sb0.5Mo0.5Se2, constituent material such as antimony (Sb), molybdenum (Mo), and selenium (Se) all 99.99% pure are procured from Alfa Aesar. These materials are mixed in stoichiometric proportion weighing 10 g and placed in a clean dry quartz ampoule of dimensions 250 mm long, 25 mm outer diameter and 22 mm inner diameter and sealed at a pressure 105 torr. Afterwards, the sealed ampoule is loaded in a temperature controlled dual zone horizontal furnace. The temperatures at the two zones i.e. source zone and growth zone are increased at the rate of 24 K/h till they reach
https://doi.org/10.1016/j.mlblux.2019.100013 2590-1508/Ó 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
2
V. Dixit et al. / Materials Letters: X 2 (2019) 100013
1353 K and 1323 K at the two zones. These temperatures are held constant for another 99 h and, then, the temperatures at the source zone and growth zone are reduced to room temperature by the rate of 12 K/h. After growth cycle completion, the ampoule is removed from the furnace, and bigger size shining crystals are observed in the ampoule having dimensions of 6 mm 4 mm and an average thickness of 35–40 lm. To check the grown crystal purity, EDAX is carried out by Phillips FESEM XL 30, (see supplementary material, Fig. 1). The EDAX analysis confirms the absence of foreign elements and the nearly stoichiometric constituent element contents in w/t%, Mo(14.35%), Sb(20.12%) and Se(65.53%). The morphological and structural properties of as grown crystals are examined by optical microscope, scanning electron microscope (SEM) and selected area electron diffraction (SAED). To evaluate their optical and vibrational properties, UV–Visible spectroscopy (Perkin Elmer Lambda 19) and Raman spectroscopy (STR 500, 532 nm excitation) were employed. To study the photo-conduction properties of the exfoliated sample, we have adopted the method presented elsewhere [18].
3. Result and discussion The surface topographic properties give direct insight of defects associated with crystal growth. The surface images of as grown crystal examined under an optical microscope (OM) is shown in
Fig. 1(a–b). In Fig. 1(a), the clean and flat surface suitable for photovoltaic and optoelectronic device applications is seen, and, in Fig. 1(b), the presence of helical spirals, confirming the crystal growth initiated from screw dislocation defect is evident [9,16]. We have presented the SEM images showing randomly oriented micron sized hexagonal shaped crystals possessing layered structure (see supplementary material, Fig. 2). The results obtained from SEM and OM analysis confirms the layered growth mechanism. To define the phase composition, a tiny crystal is ultrasonically exfoliated in acetone and its selected area electron diffraction (SAED) pattern was recorded by 200 kV TEM, as shown in Fig. 1(c). The spot like pattern is arranged in a hexagonal type pattern confirming single crystalline phase and hexagonal structure of the as grown crystal [5,16,19]. To explore the optical properties of the as grown crystal, the UV–Visible spectroscopy in the range of 600–1000 nm is performed and a sharp absorbance edge in the spectral range of 825–900 nm is observed, as displayed in Fig. 1(d). To determine the energy band gap we are presenting the plot of indirect allowed transition (ahm)1/2 versus photon energy (hm) displayed in Fig. 1(e). The extrapolation of the linear portion of the graph to fundamental absorption edge gives indirect energy band gap of 1.22 eV. One can observe few discontinuities in the Tauc plot (see supplementary material, Fig. 3a), and it may take place due to inter band transition of absorption and emission of phonons. We have adopted method presented elsewhere for making specific measurement at the point of discontinuities E1,E2, E3
Fig. 1. (a) Optical micrograph showing flat surface (b) screw dislocation (c) Electron diffraction pattern (d) absorption spectra (e) indirect energy band gap (f) Raman spectra.
3
V. Dixit et al. / Materials Letters: X 2 (2019) 100013
Fig. 2. (a) Pulse photo response of Sb0.5Mo0.5Se2 crystal recorded under a polychromatic source of intensity 50 mWcm2 (b) Single pulse response.
Table 1 Parameters of photo response of Sb0.5Mo0.5Se2 crystal compared with previous report. Material
Voltage (V)
Iph (lA)
Rk (lAW1)
D* 107 (Jones)
Tr (s)
Td (s)
References
Sb0.5Mo0.5Se2
1.00 2.00 3.00 0.30 –
4.34 8.39 11.48 1.88 0.02
543.00 1049.00 1435.00 – –
0.20 0.27 0.29 – –
0.97 0.97 0.97 4.40 3
1.00 1.00 1.00 4.50 3
This work
Sb0.1Sn0.9Se2 SnSe
and E4 [5,18]. These points are related to beginning of absorption of first phonon, second phonon and emission of second and first phonon. These four energies corresponds exactly to the non linear nature, the indirect energy band gap ‘‘Eg0 = (E1 + E4)/2 = (E2 + E3)/2” due to absorption and emission of phonon comes out to be 1.16 eV, similarly ‘‘Ep1 = (E4 E1)/2 and Ep2 = (E3 E2)/2” are the absorbed and emitted phonon energies that comes out to be 15 meV and 5 meV. The reciprocal of slope in plot of lna versus photon energy (see supplementary material, Fig. 3b) gives Urbach energy (Eu = 0.57 eV). The steepness constant ‘‘r = kBT/Eu” where kB is Boltzman constant and T is the room temperature, comes out to be 0.04. In Fig. 1(f), the Raman spectra of Sb0.5Mo0.5Se2 and MoSe2 are comparatively shown, and one can evince the presence of out of plane A1g mode in both samples at 243.55 cm1 and 243.60 cm1. A slight shift in the peak position of doped sample confirms the substitution of Sb (ionic radius 74 pm) for Mo (ionic radius 79 pm) and thus preserving the 2H-polytype of the grown crystal [16,20]. To explore the photo-conducting properties of mechanically exfoliated crystal, Keithley 2400 SMU is employed to record current versus time plot at different bias voltage and under a polychromatic source of intensity 50 mWcm2 by periodically on/off switching source. In Fig. 2(a–b), the repeatable and single pulse photo responses of cleaved crystal are given. It can be evinced from Fig. 2(a–b) that current rises quickly (rise time
[16] [14]
Tr) upon illumination (i.e. causing e-h pair generation) and, due to the presence of electric field, electrons get separated and contributes in photo-current. As the source is switched off, the photo-current decays slowly (decay time Td). It could possibly appear due to several factors. First, it could be due to mechanical exfoliation of crystal, Second, it could be due to defect states behaving as trapping centre for electrons (i.e. deep level defect states, DLDS) aroused at high temperature growth [21]. Third, as the entire experiment is carried out in an open atmosphere condition, it give a possibility of adsorption of oxygen present in the air to the surface (i.e. holding electron) and hence behaving as an additional trapping centre [9]. The photo detecting parameter such as responsivity is evaluated by (Rk = Iph/PS), where photo-current ‘‘Iph = Ion Idark”, ‘P’ is incident power and exposed area ‘S = 16 mm2’, detectivity (D* = RkS1/2/(2eIdark)1/2) [22] is presented in Table1.
4. Conclusion The single crystal of Sb0.5Mo0.5Se2 is grown by DVT technique. The chemical purity and stoichiometric proportion of constituent elements in grown crystal are confirmed by EDAX analysis. The micro morphology of as grown crystals investigated by optical
4
V. Dixit et al. / Materials Letters: X 2 (2019) 100013
microscope and SEM analysis confirms that the growth initiated at the screw dislocation defect. The structure and single crystal state verification are evidenced by electron diffraction studies. Raman spectroscopy confirms the presence of out of plane A1g vibrational mode and a slight shift in the peak position on doping confirms the substitution of Sb onto the Mo sites. The device shows quick switching action and fast response on illumination. The photocurrent, responsivity and detectivity are enhanced on increasing bias voltage from 1 to 3 V. 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. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.mlblux.2019.100013. References [1] W.H. Britton, O.H. Hugh, Churchill, Y. Yafang, J.H. Pablo, Nat. Nano 9 (2014) 262. [2] C.U. Vyas, P. Pataniya, C.K. Zankat, V.M. Pathak, K.D. Patel, G.K. Solanki, Mater. Sci. Semicond. Process. 71 (2017) 226.
[3] J. Yao, Z. Zheng, G. Yang, Appl. Mat. Int. 8 (2016) 12915. [4] H.T. Yuan, M.S. Bahramy, K. Morimoto, S.F. Wu, K. Nomura, B.J. Yang, H. Shimotani, R. Suzuki, M. Toh, C. Kloc, Nat. Phys. 9 (2013) 563. [5] A. Patel, P. Pataniya, S. Narayan, C.K. Sumesh, V.M. Pathak, G.K. Solanki, K.D. Patel, P.K. Jha, Mater. Sci. Semicond. Process 81 (2018) 108. [6] A.B. Patel, H.K. Machhi, P. Chauhan, S. Narayan, V. Dixit, S.S. Soni, P.K. Jha, G.K. Solanki, K.D. Patel, V.M. Pathak, A.C.S. App, Mater. Interfaces 11 (2019) 4093. [7] C.C. Hsiao, W.C. Lan, P. Jiang, C.M. Hui, P. Kumar, T. Taishi, 2D Mater. 1 (2014) 034001. [8] K.A. Kokh, V.V. Atuchin, T.A. Gavrilova, N.V. Kuratieva, N.V. Pervukhina, N.V. Surovtsev, Solid State Commun. 177 (2014) 16. [9] C.K. Zankat, P. Pataniya, M. Tannarana, G.K. Solanki, K.D. Patel, V.M. Pathak, Mater. Sci. Semicond. Process 91 (2019) 383. [10] C. Guo, Z. Tian, Y. Xiao, Q. Mi, J. Xue, Appl. Phys. Lett 109 (2016) 203104. [11] G.L. Frey, R. Tenne, J. Mater. Res. 13 (9) (1998) 2412. [12] W.J. Yu, Y. Liu, H. Zhou, A. Yin, Z. Li, Y. Huang, X. Duan, Nat. Nanotech. 8 (2013) 952. [13] A.K. Geim, I.V. Grigorieva, Nature 449 (2013) 419. [14] A.S. Pawbake, S.R. Jadkar, D.J. Late, Mater. Res. Express 3 (2016) 105038. [15] A.A. Tedstone, D.J. Lewis, P. O’brien, Chem. Mater 28 (2016) 1965. [16] M. Tannarana, P. Pataniya, G.K. Solanki, S.B. Pillai, K.D. Patel, P.K. Jha, V.M. Pathak, Appl. Surf. Sci 462 (2018) 856. [17] V.V. Atuchin, S.V. Borisov, T.A. Gavrilova, K.A. Kokh, N.V. Kuratieva, N.V. Pervukhina, Particuology 26 (2016) 118. [18] V. Dixit, S. Nair, J. Joy, C.U. Vyas, G.K. Solanki, K.D. Patel, V.M. Pathak, Mater. Sci. Semicond. Process 88 (2018) 1. [19] Y.M. Andreev, V.V. Atuchin, G.V. Lanskii, A.N. Morozov, L.D. Pokrovsky, S.Y. Sarkisov, O.V. Voevodina, Mater. Sci. Eng. B 128 (2006) 205. [20] Y. Liu, K. Tom, X. Zhang, S. Lou, Y. Liu, J. Yao, New J. Phys. 19 (2017) 073018. [21] M.A. Ghorbani, N.A. Enayshin, A. Kuc, G. Seifert, T. Henne, Phys. Rev. B: Condens. Matter Mater. Phys. 88 (24) (2013) 245540. [22] V. Dixit, C.U. Vyas, A.B. Patel, V.M. Pathak, G.K. Solanki, K.D. Patel, AIP Conf. Proc. 1961 (2018) 030017.