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Optical properties of Bi0.1Zn0.45VO3.1 thin films using UV-VIS-NIR spectroscopy R. Punia, R. S. Kundu, J. Hooda, Rajesh Parmar, and N. Kishore Citation: AIP Conf. Proc. 1536, 539 (2013); doi: 10.1063/1.4810339 View online: http://dx.doi.org/10.1063/1.4810339 View Table of Contents: http://proceedings.aip.org/dbt/dbt.jsp?KEY=APCPCS&Volume=1536&Issue=1 Published by the American Institute of Physics.
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Optical Properties of Bi0.1Zn0.45VO3.1 Thin Films Using UVVIS-NIR Spectroscopy R. Punia1, R.S.Kundu1, J. Hooda1, Rajesh Parmar2, and N. Kishore1 1
Department of Applied Physics, Guru Jambheshwar University of Science & technology, Hisar 125001, India. 2 Department of Physics, Maharshi Dayanand University, Rohtak 124001, India.
Abstract.
Bi0.1Zn0.45VO3.1 thin films of thicknesses 50, 100, 150, 200, and 250nm, have been fabricated from oxide glass of composition 50V2O5 - 5Bi2O3 - 45ZnO by using vacuum thermal evaporation technique. The optical properties of as-deposited thin films have been studied by using UV-VIS-NIR spectroscopy. The as-deposited thin films follow both direct allowed and direct forbidden band optical transitions with optical band gap ranging 3.85-2.70 and 3.94-3.14 respectively. The optical band gap of films decreases with increase in film thickness.
Keywords: Thin films, UV-VIS-NIR spectroscopy, optical band gap.
wavelength range 300 to 800 Å of thin films were recorded at room temperature on UV-vis-NIR spectrophotometer (Shimadzu UV-2401 PC).
INTRODUCTION V2O5 is n-type semiconductor [1] having great technological applications such as electrocromatic and electronic switches[2, 3], solar cell windows [4], cathode solid state batteries [5] etc. ZnO is also a semiconducting material that has been used for various applications like thin film solar cells, piezoelectric transducers, gas sensors etc [6]. Similarly, bismuth based layer-structured compounds are one of the most promising ferroelectric materials due to their high dielectric constants, excellent ferroelectricity, piezoelectricity and electro-optic properties [7-11]. Keeping in view the technological applications of V2O5, ZnO and Bi2O3, Bi0.1Zn0.45VO3.1 thin films of different thicknesses would be of great interest. The objective of present paper is to investigate the relationship between film thickness and optical properties of Bi0.1Zn0.45VO3.1 thin films.
RESULTS AND DISCUSSION Optical absorption spectra of Bi0.1Zn0.45VO3.1 thin films having thickness 50, 100, 150, 200, and 250 are shown in Fig. 1(a). When exceeds 104 cm-1 energy, Eopt, are related as [13-14] (1) - Eopt)]r where B is an energy independent constant and r is a constant which determines type of the optical transition. It (r) can have different values; 1/3, 1/2, 2 and 3 corresponding to direct forbidden, direct allowed, indirect allowed and indirect forbidden 1/r called Tauc’s plot [15]
!" !# , 2 and 3 but !# !" $ % suitable and shown in Figs. 1(b) and 1(c). Thus, the present thin films show both direct allowed and direct forbidden transitions.The values of Eopt for different transitions have been estimated by extrapolation of
$ %
& ' 1/r * + !" : 1.
EXPERIMENTAL Bi0.1Zn0.45VO3.1 thin films of thicknesses 50, 100, 150, 200, and 250nm, were prepared from oxide glass of composition 50V2O5 - 5Bi2O3 - 45ZnO (synthesized by conventional melt-quenching method as reported in our earlier communication [12]), by using thermal evaporation technique. Corning glass slide was used as substrate, which was cleaned by using deionized water, acetone, trichloroethylene and isopropyl alcohol subsequently for 20 minutes using an ultrasonic bath and dried in vacuum oven. Thin films were deposited on the glass substrate under high vacuum (1×10-5torr) at a deposition rate of 0.1Å/s. The thickness of the deposited films was monitored by in-situ quartz crystal. The UV-visible absorption spectra, in
TABLE 1. Direct allowed and direct forbidden band gaps of Bi0.1Zn0.45VO3.1 thin films with different film thicknesses (t). Thickness of Direct allowed Direct forbidden band gap thin film (nm) band gap 50 3.85 3.94 100 3.52 3.67 150 3.35 3.57 200 3.25 3.43 250 2.70 3.14
Proceeding of International Conference on Recent Trends in Applied Physics and Material Science AIP Conf. Proc. 1536, 539-540 (2013); doi: 10.1063/1.4810339 © 2013 AIP Publishing LLC 978-0-7354-1160-9/$30.00
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Perusal of data in Table I, there is an appreciable decrease in the Eopt on increasing the thickness of thin film and the trend continues with increasing thickness and for thin film of thickness 250 nm it becomes almost equal to optical band gap of bulk glass [12]. This may be due to structural changes occurring in Bi0.1Zn0.45VO3.1 thin films with thickness. An adequate knowledge of the local structure of these thin films is necessary to resolve this variation.
CONCLUSIONS Bi0.1Zn0.45VO3.1 thin films of thicknesses 50, 100, 150, 200, and 250nm, have been fabricated from oxide glass of composition 50V2O5 - 5Bi2O3 - 45ZnO by using vacuum thermal evaporation technique. The asdeposited thin films follow both direct allowed and direct forbidden band optical transitions. The optical band gap for direct allowed and direct forbidden transitions is 3.85-2.70 and 3.94-3.14 respectively. It decreases with increase in film thickness.
ACKNOLEDGMENTS Authors are thankful to DRDO - IRDE, Dehradun, UGC (SAP), New Delhi and DST (FIST), New Delhi for financial assistance in the form of grants.
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F IGURE 1. (a)Variation of optical absorption coefficient ' '
:$ ? % !" =>
The calculated values of Eopt for all the thin films match well with the values reported for other zinc oxide, tellurium vanadate and bismuth vanadate thin films [6, 16-18].
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