THE 4th INTERNATIONAL CONFERENCE ON THEORETICAL AND APPLIED PHYSICS (ICTAP-2014)
16-17 October 2014, Denpasar-Bali, Indonesia
Characterization of ZnO Thin Films Doped with Natrium
by Sol-Gel Method
P.L. Gareso1*, N. Syuhada1, N. Rauf1, E. Juarlin1, Sugianto2 and A. Maddu2
1
Department of Physics, Faculty of Mathematics and Natural Sciences, Hasanuddin University, Makassar 90245
2
Department of Physics, Faculty of Mathematics and Natural Sciences, Bogor Institute of Culture, IPB Bogor
* Email: pgareso@gmail.com
Abstract. The characterization of ZnO films doped with natrium by sol-gel spin coating method have been studied
using the optical transmittance UV-Vis and X-ray diffraction (X-RD) measurements. The ZnO films were prepared
using zinc acetate dehydrate (Zn(CH3COO)2.2H2O), ethanol, and diethanolamine (DEA) as the precursor, solvent, and
stabilizer, respectively. For ZnO doped sample, ammonia was used as a dopand. The ZnO films were coated on a glass
substrate using spin coating at room temperature with a rate of 3000 rpm in 30 sec. The deposited films were annealed at
different temperatures from 400oC to 600oC during 60 minutes. The UV-Vis measurement results showed that the
transmittance is above 90% in the range of wavelength 400 – 800 nm. The optical energy band gap of ZnO:N after
annealing at 500oC is found to be 3.166 eV. This number is slightly smaller than the bulk ZnO. X-RD measurements
showed that the ZnO films were hexagonal wurtzite with lattice parameters are a = 3.261 Å and c = 5.229 Å. In addition,
the average grain size of ZnO:N thin film is 127.15 nm.
Keywords: Nanocrystalline, ZnO, spin-coating, transmittance.
PACS: 78.66 Hf
INTRODUCTION
EXPERIMENTAL DETAILS
ZnO film is one of II-IV compound semiconductor
that has been widely used for many devices
application such as thin film sensors [1], light emitting
diodes [2], spintronic devices [3] and nanolasers [4].
Also, ZnO thin film is used as solar cell window since
it has high optical transmittance in the visible region.
Furthermore, ZnO has a large band gap of 3.3 eV,
large exitonic binding energy of 60 meV and high
carrier mobility at room temperature.
Various techniques have been applied for
fabricating ZnO thin film such as sputtering [3,4],
molecular beam epitaxy (MBE) [5,6], spray pyrolysis
[7], pulse laser deposition (PLD) [8,9], and sol gel
method [10-11]. Sol-gel technique is widely used for
fabrication of transparent and conductive oxide due to
its simplicity, no vacuum system needed and low cost
for large area coating. In addition to this, the sol-gel
method offers advantages such us easy to control of
chemical compound, high surface morphology at low
crystallizing temperature.
In this present study, we investigate the structural
and optical properties of ZnO thin films doped with
natrium deposited by sol-gel method on a glass
substrate. The films were characterized by X-ray
diffraction and optical transmittance UV-Vis. The
SEM was performed to observe the surface of the ZnO
thin films.
The ZnO thin films doped with natrium were
prepared using (Zn(CH3COO)2.2H2O), ethanol, and
diethanolamine (DEA) as a starting material, solvent
and stabilizer, respectively. The ZnO:N thin films
were deposited on a glass substrate by spin coating
method with a speed of 3000 rpm for 30 second. After
deposition by spin coating, the films were dried at
300oC for 15 min in a furnace to evaporate the solvent
and to remove an organic solvent. Then, the films were
inserted to the tube furnace and annealed at various
temperatures from 400oC to 600oC for 60 minutes.
The surface morphology of the films was evaluated
using Scanning electron microscopy (SEM). The
thickness of the film was measured by SEM. X-ray
diffraction (X-RD) EMMA GBC was used to
investigate the structural properties of ZnO:N films
using a single scan diffractometer with Cu Kα (λ =
1.5406 Å) radiation and scanning range of 2θ between
20o and 70o. During the measurement, the current and
the voltage of X-RD were maintained at 25 mA and 35
kV, respectively and the scan speed was 2o/min. The
transmission spectra of the films were measured by a
single beam of The UV-Vis spectrophotometer with a
wavelength of 250-800 nm. From the transmittance
spectra the band gap energy of ZnO:N thin films was
obtained.
1
THE 4th INTERNATIONAL CONFERENCE ON THEORETICAL AND APPLIED PHYSICS (ICTAP-2014)
16-17 October 2014, Denpasar-Bali, Indonesia
RESULTS AND DISCUSSION
Figure.1a shows the SEM micrographs of ZnO
doped with nitrogen after annealing at 400oC deposited
on glass substrate. As shown in this figure, the surface
of the ZnO films has a smooth surface and uniformly
covering the overall. Also, the SEM image shows the
grains uniformly distributed without cracks and pores
were observed. Figure.1b depicts the thickness of the
ZnO:N films. From a cross section of the films
(figure.1b), the thickness of the films is 920 nm. This
number is used to calculate the bandgap energy of
ZnO:N films.
(a)
Fig.2. X-RD spectra of ZnO thin films doped with natrium
before and after annealing at various temperatures from
400oC to 600oC for 60 minutes
(b)
Fig.1. (a) The SEM image of ZnO:N thin films after
annealing at 400oC. (b) The SEM image of the cross section
of ZnO:N.
Figure 2 displays the X-ray diffraction pattern of
ZnO thin films doped with natrium before and after
annealing at different annealing temperature from
400oC to 600oC. It was clearly seen that in the asgrown sample of ZnO:N, the X-RD spectra appears at
36.2o, 47.6o, 56.7o, 62.9o which are corresponded to
(101), (102), (110), and (103) plane, respectively.
After annealing at 500oC and 600oC, more additional
peak was observed at 31.7o, and 34.4o. These peaks are
related to (100) and (002) plane. Althought the X-RD
peak at the plane of (002) is weak, our calculation
shows that the ZnO:N thin films have polycrystalline
wurtzite hexagonal structure as shown in Table.1.
Table.1. Lattice parameters of ZnO:N before and after
annealing at various temperatures.
Sampel
a (Å)
Standar (Å)
c (Å)
As-grown
3.252
5.200
400° C
3.265
5.239
500° C
3.286
5.284
600° C
3.244
5.195
3.246
Standar (Å)
5.209
From the XRD spectrum, grain size (D) of the film
is calculated using the Debye Scherrer formula [12],
D = 0.9λ/β cosθ
Where, λ, β, and θ are the X-ray wavelength, full
width at half maximum (FWHM) and Bragg angle
respectively. Table.2 shows the structural parameters
of ZnO:N thin films.
Table.2. Structural parameters of ZnO thin films
doped with natrium before and after annealing at
various temperatures
Sample
As-grown
400oC
500oC
As-grown
400oC
500oC
As-grown
400oC
500oC
Plane
100
002
101
FWHM
0.2373
0.0587
0.1746
0.1610
0.1682
0.1751
0.2328
0.0905
0.1376
2 θ(deg)
31.70
31.77
31.81
34.44
34.49
34.49
36.28
36.21
36.33
d(Å)
2.8163
2.8272
2.8458
2.5999
2.6193
2.6418
2.4764
2.4880
2.5055
2
THE 4th INTERNATIONAL CONFERENCE ON THEORETICAL AND APPLIED PHYSICS (ICTAP-2014)
16-17 October 2014, Denpasar-Bali, Indonesia
7e+15
6e+15
4e+15

hv eV
5e+15
3e+15
2e+15
3,166 eV
1e+15
0
1.0
1.5
2.0
2.5
3.0
3.5
4.0
hv (eV)
Fig.3.The transmittance spectra of ZnO thin films undoped
and doped with natrium after annealing at 500oC for 60
minutes.
Figure 3 shows the optical transmitance spectrum
of undoped and natrium doped ZnO films after
annealing at 500oC. It was clearly observed in this
figure that both undoped and doped samples show
similar transmittance profil. The tansmittance value is
below 90% at wavelength less than 400 nm and
increase up to 90% for wavelength of 400 nm to 800
nm. In addition to this, sharp absorption edge was
clearly observed which is located at 380 nm which is
due to the fact that the ZnO is a direct band gap
semiconductor. The corresponding optical band gap of
ZnO thin films is estimated by extrapolation of the
linier relationship between (αhυ)2 and hυ according to
the equation [10].
(𝛼ℎ𝜐)2 = 𝐴(ℎ𝜐 − 𝐸𝑔 )
Where α is the absorption coefficient, hυ is the photon
energy, Eg is the optical band gap and A is aconstant.
Based on this equation the band gap energy of ZnO
thin films is determined.
Figure.4 depicts the plot of (αhυ)2 as a function
photon energy (hυ). The band gap energy is
determined from the intercept of (αhυ)2 vs (hυ). From
the intercept, the band gap energy of ZnO thin films
doped with natrium after annealing at 500oC is found
to be 3.166 eV. This value is slightly smaller than that
the bulk ZnO of 3.37 eV. This difference is due to the
grain boundary and the defect that forming during the
depossition of the films.
Fig.4.The plot of (αhυ)2 vs photon energy of ZnO thin films
doped with natrium after annealing at 500oC for 60 minutes.
SUMMARY
We have investigated the structural and optical
characterization of undoped and doped natrium ZnO
thin films grown by sol-gel spin coating before and
after annealing using x-ray diffraction and optical
transmitance UV-Vis diffractophotometer. X-RD
measurement shows that more additional peak appears
after annealing compare to as-grown thin films. In
addition to this, all the samples show the
polycrystalline wurtzite hexagonal structure with
lattice parameters are a = 3.261 Å and c = 5.229 Å.
The optical band gap energy of the films after
annealing at 500oC is 3.166 eV. This value is sligthly
smaller than that bulk ZnO.
ACKNOWLEDGMENTS
The P.L.G acknowledges the financial support
from the higher education of Indonesia (DIKTI)
through out LP2M-UNHAS under contract number of
16187/UN4-42/PL.09/2014.
REFERENCES
1. S. T. Shishiyanu, T. S, Shishiyanu and O. I. Lupen,
Sensors and Actuators B: Chemical, 107, 379-386
(2005).
2. N. Saito, H. Haneda, T. Sekiguchi, N. Ohashi, I.
Sakaguchi and K. Koumoto, Advanced Materials,
14, 418-421 (2002).
3. T. Meron and G. Morkovich, Journal of Physical
Chemistry B, 109, 20232-20236 (2005)
3
THE 4th INTERNATIONAL CONFERENCE ON THEORETICAL AND APPLIED PHYSICS (ICTAP-2014)
16-17 October 2014, Denpasar-Bali, Indonesia
4. M. H. Huang, S. Mao, H. Feick, H. Yan, Y. Wu, H.
Kind, E. Weber, R. Russo and P. Yang, Science,
292, 1897-1899 (2001)
5. C. Jagadish, and S. Pearton (Editors), Zinc Oxide
Bulk, Thin Film and Nanostructures, Elsevier,
2006.
6. P. Nanes, D.Costa, E. Furtunato and R. Martins,
Vacuum, 64, 293-297 (2002)
7. S. Mondal, K. P. Kanta and P.Mitra, Journal of
Physical Sciences, 12, 221-229 (2008).
8. M. Krunks and E. Mellikov, Thin Solid Films, 270,
33-36 (1995).
9. X. L. Wu, G. G. Siu, C. L. Fu, and H. C. Ong,
Appl. Phys. Lett, 78, 2285-2287 (2001)
10.M. Caglar, S. Ilican, and Y. Caglar, Thin Solid
Films, 312, 5023-5028 (2009).
11. E. J. Luna-Arredondo, A. Mmaldonado, R.
Asomoza, D. R. Acosta, M. A. Melendez-lina and
M. de la L. Olvera, Thin solid Film, 490, 132-136
(2005).
12. Z. R. Khan, M. Zulfequar, and M. S. Khan,
Materials Science and Engineering:B, 174, 145149 (2010).
4