Third Day Poster Session, 17 June 2010 - NanoTR-VI

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P mP
P vs.
P =
P,P
P (1)
P and
Poster Session, Thursday, June 17
Theme F686 - N1123
Influence of Annealing Conditions on Optical Properties of ZnO Thin Films
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UDerya BaharUP P*, Göknil BabürP P, Sinan DikenP P, Tuba Aye TermeliP P, Banu ErdoanP P, Sava SönmezoluP
Pand Güven ÇankayaP
1
PDepartment of Physics, Faculty of Arts and Science, Gaziosmanpaa University, Tokat 60250, Turkey
Abstract-ZnO thin films were deposited on soda lime glass substrates by sol–gel spin-coating technique. The optical properties of ZnO thin films
are investigated for different annealing temperatures. The optical band gaps of thin film are found to vary with annealing temperatures. The
obtained films are also transparent in the UV- visible region
1
Zinc oxide (ZnO) as a wide-band-gap semiconductor has
attracted much attention in current semiconductor research,
due to its superior optical properties. In addition, ZnO is a
versatile semiconductor material, which has attracted attention
for its wide range of applications, such as thin films, solar
cells, luminescent, electrical and acoustic devices and
chemical sensors [1-2].
In this paper, we report the investigation of ZnO thin films
prepared by sol-gel spin coating process using zinc acetate
(ZnAc). The optical characterization is investigated for
different annealing temperatures using Perkin Elmer Lambda
35 UV-VIS Spectrometer at room temperature.
Transmittance (%)
100
80
60
40
20
0
200 400 600 800 1000 1200
Wavelenght (nm)
200 C 0
300 C 0
400 C 0
500 C 0
Figure 1. UV–VIS spectra of the ZnO thin film for various
temperatures.
In order to prepare a ZnO solution, first, 3.35gr zinc acetate
(Zn(CHR3RCOO)R2R·2HR2RO, Merck), used as a precursor, was
dissolved in 50 ml ethanol [CR2RHR6RO, Merck] and stirred for 5
0
min at 60 P PC in a magnetic mixture. Then, 5 ml glacial acetic
acide [CR2RHR4ROR2R, Merck] and 1.5 ml hydrochloride acid (HCl,
Merck) were added in the solution, and the final solution was
subjected to the magnetic mixture for 2 h. Here, glacial acetic
acid and hydrochloride acid were used as an inhibitor to slow
down the zinc acetate fast hydrolysis. Prior to the coating
process, the glass was washed with water, ultrasonically
cleaned in ethanol for 20 min, and in acetone for 20 min,
respectively. The deposition was carried out at a spinning
speed of 3000 rpm for 30 s. The spin coating procedure was
0 0 0
continuously repeated five times at 200P PC, 300P PC, 400P PC and
0
500P PC annealing temperatures on glass substrate.
Fig. 1 shows the UV–VIS spectra ZnO thin films for
different annealing temperatures in wavelength range 300–
1100nm. The transmission of the thin films of zinc oxide
decreases with the increase in annealing temperature. This can
be linked with the increase in the grain size, and indicating its
high surface roughness and inhomogeneity [3].
(h v) 2 (eV/m) 2
20
16
12
8
4
200 C 0 , E g
= 3.84 eV
300 C 0 , E g
= 3.74 eV
400 C 0 , E g
= 3.67 eV
500 C 0 , E g = 3.58 eV
0
2.4 2.8 3.2 3.6 4
Photon energy (eV)
Figure 2. UV–VIS spectra of the ZnO thin film for various
temperatures.
The optical band gap of the film was calculated by the
following relation [4]:
(hv) = A (hv - ERgR) P
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where A is an energy-independent constant between 10P
8 -1
10P
P, Eg is the optical band gap and r is a constant, which
determines type of optical transition, r = 1/2, 2, 3/2 or 3 for
allowed direct, allowed indirect, forbidden direct and
forbidden indirect electronic transitions, respectively [4]. The
1/r
r
(hv)P hv curves were plotted for different r values and
the best fit was obtained for r = ½. The film at various
annealing temperatures shows a direct allowed transition. The
optical band gap was determined by extrapolating the linear
2
portion of the plots to (hv)P 0. The optical band gaps of the
thin film were found to be 3.84, 3.74, 3.67 and 3.58 eV at 200 °C,
300 °C, 400 °C and 500 °C annealing temperature, respectively.
The thicknesses of ZnO film were also determined from
transmittance measurements in Fig.1 and found to be 1361, 692,
939 and 660 nm, respectively. The optical band gap decreases
with the increasing annealing temperatures. The decrease in
the optical band gap is attributed to the lowering of the
interatomic spacing, which may be associated with a decrease
in the amplitude of atomic oscillations around their
equilibrium positions [5].
In summary, the analysis of the transmission spectra shows
that ZnO thin films are transparent in the UV-visible region
irrespective of the annealing temperatures. This work was
partially supported by the Scientific Research Commission of
Gaziosmanpaa University (Project No: 2009/29).
*Corresponding author: HTbhr_dry@hotmail.comT
[1] Y. Chen, D.M. Bagnall, Z. Zhu, T. Sekiuchi, K. Park, K. Hiraga,
T. Tao, S. Koyama, M.Y. Shen, T. Goto, J. Cryst. Growth 181 (1997)
165.
[2] S. Saito, M. Miyayama, K. Koumoto, H. Yanagida, J. Am. Ceram.
Soc. 68 (1985) 40–43
[3] K. Liu, X. Wu, B. Wang, Q. Liu, Mater. Res. Bull. 37 (2002)
2255.
[4] J. Tauc, Mater. Res. Bull. 5 (1970) 721.
[5] S. Sönmezolu, G. Çankaya,P PN. Serin, T. Serin, Int. Conf. on
Nanomaterials and Nanosystems, 10-13 August 2009, p. 129.
6th Nanoscience and Nanotechnology Conference, zmir, 2010 619