Materials Sciences and Applicatio n, 2011, 2, 765-770
doi:10.4236/msa.2011.27105 Published Online July 2011 (http://www.SciRP.org/journal/msa)
Structural and Dielectric Properties of Sintering
Zinc Oxide Bulk Ceramic
Mariem Chaari*, Adel Matoussi, Zouheir Fakhfakh
1Laboratory of Composite Ceramic and Polymer Materials, Scientific Faculty of Sfax, Tunisia, Africa.
Received April 2nd, 2011; revised April 22nd, 2011; accepted April 30th, 2011.
ABSTRACT
Undoped zinc oxide (ZnO) has been prepared at various growth temperatures by conventional sintering process. The
morphology and crystalline properties of ZnO pellets were examined by scanning electron microscopy, atomic force
microscopy and X-ray diffraction. It has revealed that the grain size and surface roughness tends to increase by in-
creasing the sintering temperature. XRD analysis showed that all samples are polycrystalline with a hexagonal wurtzite
structure. The alignment of ZnO grains along the (10.0) plane was enhanced as the temperature increased. Interestingly,
the compressive stress was found to decrease drastically from –0.62 GPa at 700˚C to –0.2 MPa at 1000˚C. This im-
provement in film structure seems to enhance considerably the dielectric properties for the samples sintering at high
temperatures. Results show an increase of dielectric constant and a decrease of electrical resistivity when increasing
the sintering temperature.
Keywords: Zinc Oxide, Sintering Process, Micro Strain, Impedance Spectroscopy
1. Introduction
During the last few decades, zinc oxide (ZnO) has at-
tracted much interest in science and technology due to its
versatile properties such as transparency in the visible
range, direct band gap (3.37 eV), absence of toxicity,
abundance in nature, etc. These characteristics find a wide
range of applications in opto-electronic and electronic de-
vices [1-7]. For example, it used in solar cells [1], trans-
parent conducting films, chemical sensors [2,3], varistors
[4,5], light-emitting diodes[6], laser diodes [7], etc.
The preparation of high quality ZnO thin films has
been the subject of continuous research. Many tech-
niques are used for preparing zinc oxide such as: RF
sputtering [8], chemical vapour deposition [9], sol-gel
process [10], carbothermal reduction method [11] and
pressurized melt growth [12,13], among others. The
conventional sintering process has the advantages of be-
ing cheap, easy-to-use, safe and able to be implemented
in a standard laboratory. It is well known that the opto-
electronic properties of ZnO are affected by the prepara-
tion conditions such as working pressure, substrate tem-
perature, types of substrates, thickness of the films and
annealing temperature.
The present paper is devoted to examine the influ-
ence of sintering temperature on the structure, mor-
phological and the dielectric properties of ZnO tablets.
2. Experimental Procedure
Undoped ZnO pellets were prepared by the conventional
sintering technique in an atmospheric heated furnace
using zinc oxide powders (Aldrich-GmbH, purity ≈99%).
The ZnO powders were first milled in an agate mortar
and heated in air at annealing temperature of 300˚C for 2
hours to evaporate the water and remove the organic re-
siduals. The obtained powders were then pressed into
pellet disks (of about 1mm thickness and 8 mm diameter)
and sintered at various temperatures (700˚C - 1000˚C) in
ambient air for 3 hours. Finally, these pellets were rapidly
quenched to room temperature in air in order to freeze the
structure. The crystalline structure and surface morphol-
ogy of the sintered specimens were characterized by
X-ray diffraction (XRD), scanning electron microscopy
(SEM) and atomic force microscopy (AFM). The spec-
trometer dielectric was used to characterize the dielectric
properties of the obtained samples.
3. Results and Discussions
3.1. Structural Properties
The ZnO structure is examined by θ - 2θ X-ray diffrac-
tion (XRD) measurements. Figure 1 shows the XRD

Structural and Dielectric Properties of Sintering Zinc Oxide Bulk Ceramic 766
patterns of ZnO prepared at growth temperature ranging
from 700˚C to 1000˚C. All the samples exhibit a poly-
crystalline hexagonal structure. The peaks are identified
to (10.0), (00.2), (10.1), (10.2), (11.0) and (10.3) plane
reflections for wurtzite phase of ZnO according to the
standard JCPDS data file (No. 36-1451). One can see that
the ZnO growth appears to be randomly oriented along
the (10.1) plane instead of c-axis (00.2) direction.
In order to evaluate the texture coefficient and the per-
centages in volume of oriented crystallites in the <hk.l>
direction, we have used the well-known formula reported
in Ref. [14] and results are given in Table 1.
It is found that the highest value of texture coefficient
(TC) corresponds to (10.1) plane which contributes about
47 % of oriented ZnO grains. We notice a slight decrease
of the contribution of (00.2) phase on detriment to the
(10. 1) one as the sintering temperature is varied from
700˚C to 1000˚C. Figure 2 shows that the intensity of the
(10.1) peak compared to the neighboring (10.0) and (00.2)
increases by increasing the sintering temperature from
700˚C to 1000˚C. This result indicates that (10.1) is the
preferred orientation of ZnO pellet growth. In addition,
the full width at half maximum (FWHM) for ZnO (10.1)
peak decreases from 0.24˚ to 0.12˚ when the temperature
increases from 700˚C to 1000˚C respectively.
The dependence of the growth temperature on the
grain size, the angle position and FWHM for ZnO (00.2)
diffraction peak are illustrated in Table 2. The average
grain size of ZnO is calculated using the Scherer’s Equa-
tion [15]:
0.9
DBcos



where D is the grain size, λ is the wavelength of the
X-ray radiation used, B is the full width at half maximum
(FWHM) of the diffraction peak and θ is the Bragg dif-
fraction angle of the XRD peak.
Figure 1. XRD patterns of ZnO prepared at various Sinter-
ing temperatures.
700 750 800
0,45
0,50
0,55
0,60
0,65
0,70
0,75
Sintering temperature (˚C)
Figure 2. Evolution of intensity ratio of XRD peaks as a
function of sintering temperature.
The crystallite size increases from approximately 38
nm at 700˚C to 52 nm at 900˚C. As the temperature in-
creases, we observe a neat decrease of the full width at
half maximum of the (00.2) peak. Furthermore, the (00.2)
peak position shifts to higher angles and reaches the val-
ue 34.408˚ of free-strained ZnO film [16].
Here, it must be pointed that the crystal quality of ZnO
can be improved at higher sintering temperature [17-19].
This behavior can be explained by the reduction of the
density defects and atom vacancies caused by the in-
crease of the diffusion of oxygen and zinc atoms at ele-
vated temperature. According to Bachari [20], the lack of
oxygen atoms may result in the growth of non-stoi-
chiometric thin films and bad crystalline phases.
It has been reported that the crystalline properties and
alignment of the ZnO thin films depends strongly on the
substrate temperature and the O2 concentration during
growth. Vimalkumar et al. [21] showed that with in-
crease in the spray pyrolysis rate orientation of ZnO
grains changed from (10.1) to (00.2) plane. Matsuka and
Ono [22] have observed that the increase of oxygen par-
tial pressure from 0 to 0.12 Pa leads to change of crystal-
line orientation from (10.1) to (00.2) plane. Prasada et al.
[23] showed that ZnO grows randomly along the (10.1),
(00.2) and (10.0) orientations. They found that the stress
value decreases whereas the particle size increases as the
growth temperature increased.
In our case, the lattice strain εzz and residual stress σ in
the grown ZnO samples are estimated using the follow-
ing expressions [24]:

2
1333 1112
13
2CC CC
= 2C
z
z




and
0
0
cc
=c
zz


2

(°)
45 50 55 60
T
s
=1000°C
T
s
=850°C
T
s
=700°C
25 30 35 40
XRD Intensity (u.a)
(11-20)
(10-12)
(10-11)
(0002)
(10-10)
850900950 1000
I10.1/(I10.0+I00.2+I10.1)

Structural and Dielectric Properties of Sintering Zinc Oxide Bulk Ceramic 767
Table 1. Texture coefficient and percentages of oriented crystallites in <hk.l> direction.
Ts (˚C)
Texture coefficient
TC(10.0) TC(00.2) TC(10.1)
±0.0005 ±0.0003 ±0.0004
Percentage of oriented crystallites (%)
χ(10.0) χ(00.2) χ(10.1)
700 0.648 1.299 2.355 12.96 ± 0.008 25.99 ± 0.011 46.11 ± 0.012
800 0.639 1.312 2.345 12.78 ± 0.011 26.24 ± 0.020 47.10 ± 0.009
900 0.655 1.249 2.369 13.09 ± 0.007 24.98 ± 0.006 47.38 ± 0.004
1000 0.645 1.268 2.406 12.91 ± 0.005 25.36 ± 0.004 48.13 ± 0.003
Table 2. Variations of grain size and FWHM for ZnO (00.2) reflection with temperature.
Ts (˚C) FWHM of the
(00.2) peak (˚) Diffraction angle 2θ(˚) Grain size D(nm)
700 0.236 34.323 38.221 ± 0.021
800 0.209 34.353 41.323 ± 0.018
850 0.183 34.386 47.194 ± 0.011
900 0.168 34.403 51.407 ± 0.017
1000 0.172 34.420 50.212 ± 0.013
where c0 and c are the lattice parameters of unstrained
and the prepared ZnO samples respectively. C11 = 209.7
GPa, C12 = 121.1 GPa, C13 = 105.1 GPa and C33 = 210.9
GPa are the elastic stiffness constants of bulk ZnO [23].
0
5
10
15
20
25
30
700800850900 1000
Sintering temperature (°C)

zz
x10
-4
(a.u)
-65
-55
-45
-35
-25
-15
-5
 (x10
7
Pa)
Figure 3 shows the variation of lattice strain and re-
sidual stress in ZnO as a function of the growth tempera-
ture. The sample sintered at 700˚C has larger strain and
stress values. One can see that the residual stress is com-
pressive which decreases negatively from –0.62 GPa at
700˚C to –0.2 MPa at 1000˚C. This means that elevated
temperature in the range 900˚C - 1000˚C are favoured to
obtain better crystalline quality of ZnO prepared by con-
ventional sintering process. According to Prasada [23], the
measured stress in ZnO is attributed mainly to intrinsic
origins introduced by the presence of impurities defects
and lattice distortions in the crystal. The extrinsic stress
induced by the lattice and the thermal mismatches will not
be generated because the pellet is thicker (1 mm - 2 mm)
and because of the non-use of growth substrate in our
experiment.
Figure 3. Variation of lattice strain and residual stress in
ZnO tablet s.
Table 3. EDX analysis of the Zinc oxide samples.
Sintering
temperature(˚C) O (at %) Zn (at %)
700 50.568 ± 0.008 48.144 ± 0.006
850 50.043 ± 0.005 48.244 ± 0.009
900 49.752 ± 0.011 48.76 ± 0.011
1000 49.412 ± 0.012 49.78 ± 0.013
Moreover, it is shown that the intrinsic stress appears
frequently in nonstoichiometric films [23,25]. This seems
to be consistent with energy dispersive X-ray (EDX)
analysis presented in the Table 3. It is seen clearly that the
sample composition became more stoichiometric with in-
creasing the sintering temperature. For all the samples, the
level of incorporation impurity is reduced to an amount
lesser than 1.5% and the percentages of oxygen and the
zinc are nearly equal. Consequently, it reveals that the
growth at high temperature (>1000˚C) can strongly en-
hance the physicochemical properties and thus improve the
crystallinity of the ZnO films.
pellets sintered at 850˚C, 900˚C and 1000˚C. For all
samples, the surface is rough and presents grains of crys-
tallites having very varied shapes and nanometric sizes.
These crystallites are randomly distributed and irregu-
larly disoriented. With increasing the sintering tempera-
ture, the grain size is found to increase whereas its den-
sity decreases resulting from conglomeration or coales-
cence of smaller grains.
Here, it is evident that the sintering temperature exer-
cises strong effects on the surface morphology and the
crystal quality of ZnO powders.
3.2. Morphological Properties
Figure 4 shows the scanning electron micrographs of ZnO

Structural and Dielectric Properties of Sintering Zinc Oxide Bulk Ceramic 768
Figure 4. Plan view of SEM micrographs of ZnO pellets
sintered at 850˚C (a); 900˚C (b); and 1000˚C (c).
From AFM analyses, the rms roughness increases from
9 nm to 68 nm as the deposition temperature increases
from 700˚C to 1000˚C. This agrees well with the results
of XRD measurements. We surmise that at high tem-
perature, the atoms have enough diffusion activation en-
ergy to occupy the proper sites in the crystal lattice and
grains with the lower surface energy become larger at
high temperature [26]. These results show that the high
temperature enhances the coalescence of grains and thus
the lateral growth of ZnO along the <10.1> direction.
3.3. Dielectric Analysis
Figure 5 presents the variation of the dielectric constant
measured at room temperature for different frequency as
a function of the sintering temperature. The dielectric
constant was decreased as the measuring frequency in-
creased. For the sample sintered at 1000˚C the ε value
decreased from 900 at 1 Hz to 12.27 at 2 kHz and to 4 at
1 MHz. Also, it shows an increase tendency of all the
dielectric constants with increasing the sintering tem-
perature from 700˚C to 1000˚C.
(a)
These behaviours may be attributed to the enhance-
ment of grain size, compactness and the structural quality
of the material [25-27]. Figure 6 illustrates the evolution
of electrical resistivity with increasing the sintering tem-
perature. The resistivity was first decreased reaching a
minimum value 4 × 109 Ω·cm at 850˚C and then in-
creased with increasing temperature. A similar behaviour
has been observed by Gomes [28] and Olivera [29] in
Ga- doped and F-doped ZnO thin films, respectively.
(b)
The measured values of resistivity are in range 109 -
1010 Ω·cm which indicates that our prepared ZnO bulk
possess an insulating behaviour rather than n-type semi-
1
10
100
1000
650750850950 1050
Sintering temperature (°C)
Dielectric constant (a.u)
1Hz
100Hz
10KHz
1MHz
(c)
Figure 5. Vari atio n of the di elec tric constant as a func tion of
the sintering temperature.
1
5
9
13
17
650 750850 9501050
Sintering temperature (°C)
Resistivity (x10
9
Ω.cm )
Figure 6. Evolution of electrical resistivity versus the sin-
tering temperature.

Structural and Dielectric Properties of Sintering Zinc Oxide Bulk Ceramic769
conductor character. However, the decrease of resistivity
with elevation of growth temperature is due, on the one
hand, to both the improvement in the pellet structure and
the reduction of grain boundaries which enhance the free
electron mobility [30]. On the other hand, the reduction
in the resistivity can also be due to the non-stoichiometry
of the film and the presence of residual impurities (K, Ca,
S, and Fe) which can substitute the Zn atoms and/or be
incorporated in oxygen vacancies [28,29,31].
For samples sintered at higher temperatures, the in-
crease in resistivity can be associated to more appropriate
stoichiometry, the increase of ZnO grain size and the
scattering of free carriers at grain boundaries in poly-
crystalline ZnO pellets [23-25]. Here, it is important to
notice that high temperature can enhance the crystalline
and the dielectric properties of ZnO pellets.
As schown in Figure 7, the lowest value of dielectric
loss at higher frequencies (tg δ = 6.6 × 10–2) is found for
the ZnO sample sintered at 900˚C. Due to their good di-
electric properties, low dielectric loss, and high electrical
resistivity. ZnO can be used as a promising material for
fabrication of dielectric varistors and transparent elec-
trodes in solar cells.
4. Conclusions
In this paper, we study the effect of growth temperature
on the structural and dielectric properties of zinc oxide
prepared by conventional sintering process. The mor-
phology and the crystalline characteristics of ZnO films
were examined by scanning electron microscopy, atomic
force microscopy, and X-ray diffraction. It has revealed
that the grain size and surface roughness tends to increase
and that the crystalline quality of ZnO film is better en-
hanced by increasing the sintering temperature.
XRD analysis showed that all films are polycrystalline
with a hexagonal wurtzite structure and randomly ori-
ented (10.1) direction. The residual stress in ZnO sample
0,00
0,05
0,10
0,15
0,20
0,25
0,30
0,35
0,40
700 750800 850 900 95010001050
Sintering temperature (°C)
Dielectric loss (u.a)
f=1MHz
f=10M Hz
Figure 7. Variation of the dielectric loss versus the sintering
temperature.
is compressive which decreases significantly from –0.62
GPa at 700˚C to –0.2 MPa at 1000˚C. The temperature
dependence of electrical resistivity and dielectric constant
were studied at room temperature for different frequen-
cies ranging from 10–1 Hz until 10 MHz. Results show an
increase of dielectric constants with increasing the sin-
tering temperature and a decrease with changing the
measuring frequency. This effect is attributed to the in-
crease of grain size, deviation from stoichiometry and the
decrease in sample strain.
Electrical resistivity was determined to be in the range
4 × 109 - 2.4 × 1010 Ω·cm indicating a more dielectric be-
haviour than a semi-conducting character. All the above
results show that the sample sintered at 900˚C has the best
dielectric properties and a good crystalline structure.
REFERENCES
[1] S. Gledhil, A. Grimm, A. Allsop, T. Koehler, C. Camus,
L. Lux-Steiner and C.-H. Fisher, “A Spray Pyrolysis
Route to the Undoped ZnO Layer of Cu(In,Ga)(S,Se)2
Solar Cells,” Thin Solid Films, Vol. 517, No. 7， 2009, pp.
2309-2311. doi:10.1016/j.tsf.2008.10.110
[2] S. Major and K. L. Chopra, “Indium-Doped Zinc Oxide
Films as Transparent Electrodes for Solar Cells,” Solar
Energy Materials, Vol. 17, No. 5, 1988, pp. 319-327.
doi:10.1016/0165-1633(88)90014-7
[3] S. T. Shishiyanu, T. S. Shishiyanu and O. I. Lu-
pan,“Sensing Characteristics of Tin-Doped ZnO Thin
films as NO2 Gas Sensor,” Sensors and Actuators B:
Chemical, Vol. 107, No. 1, 2005, pp. 379-386.
doi:10.1016/j.snb.2004.10.030
[4] T. K. Gupta and J. Am, “Application of Zinc Oxide
Varistors,” American Ceramatic Society, Vol. 73, No. 7,
1990, pp. 1817-1840.
doi:10.1111/j.1151-2916.1990.tb05232.x
[5] S. Anas, R. V. Mangalaraja, M. Poothayal, S. K. Shukla
and S. Ananthakumar, “Direct Synthesis of Varistor-
Grade Doped Nanocrystalline ZnO and Its Densification
through a Step-Sintering Technique,” Acta Materialia,
Vol. 55, No. 17, 2007, pp. 5792-5801.
doi:10.1016/j.actamat.2007.06.047
0.40
0.35 [6] Y. I. Alivov, E. V. Kalinina, A. E. Cherenkov, D. C. Look,
B. M. Ataev, A. K. Omaev, M. V. Chukichev and D. M.
Bagnall, “Fabrication and Characterization of n-ZnO/
p-AlGaN Heterojunction Light-Emitting Diodes on
6H-SiC Substrates,” Applied Physics Letters, Vol. 83, No.
23, 2003, pp. 4719-4721. doi:10.1063/1.1632537
0.30
0.25
0.20
0.15
[7] H. S. Kim, F. Lugo, S. J. Pearton, D. P. Norton, Y. L.
Wang and F. Ren, “Phosphorus Doped ZnO Light Emit-
ting Diodes Fabricated via Pulsed Laser Deposition,” Ap-
plied Physics Letters, Vol. 92, No. 11, 2008, pp. 112108-
112110. doi:10.1063/1.2900711
0.10
0.05
0.00
[8] X. H. Yu, J. Ma, F. Ji, Y. H. Wang, X. J. Zhang and H. L.
Ma, “Influence of Annealing on the Properties of ZnO: Ga
Films Prepared by Radio Frequency Magnetron Sputter-
ing,” Thin Solid Films, Vol. 483, No. 1-2, 2005, pp.

Structural and Dielectric Properties of Sintering Zinc Oxide Bulk Ceramic 770
296-300. doi:10.1016/j.tsf.2005.01.013
[9] J. Hu and R. G. Gordon, “Atmospheric Pressure Chemical
Vapor Deposition of Gallium Doped Zinc Oxide Thin
Films from Diethyl Zinc, Water, and Triethyl Gallium,”
Journal of Applied Physics, Vol. 72, No. 11, 1992, pp.
5381-5392. doi:10.1063/1.351977
[10] K. Y. Cheong, N. Muti and S. R. Ramanan, “Electrical
and optical studies of ZnO: Ga Thin Films Fabricated via
the Sol-gel Technique,” Thin Solid Film, Vol. 410, No.
1-2, 2002, pp. 142-146.
doi:10.1016/S0040-6090(02)00286-9
[11] A. Zaier, F. Oum Elaz, F. Lakfif, A. Kabir, S. Boudjadar
and M. S. Aida, “A Novel Synthesis of Nanostructured
ZnO via Thermal Oxidation of Zn Nanowires Obtained by
a Green Route,” Metirial Science in Semiconductor Proc-
essing, Vol. 12 ,2009, pp. 279-284.
[12] J. Nause and B. Nemeth, “Pressurized Melt Growth of
ZnO Boules,” Semiconductor Science and Technology,
Vol. 20, No. 4, 2005, p. S45.
doi:10.1088/0268-1242/20/4/005
[13] K. Jacobs, D. Schulz, D. Klimm and S. Ganschow, “Melt
Growth of ZnO Bulk Crystals in Ir Crucibles,” Solid State
Sciences, Vol. 12, No. 3, 2010, pp. 307-310.
doi:10.1016/j.solidstatesciences.2009.05.015
[14] Y. Caglar, S. Aksoy, S. Ilican and M. Cagmar, “Crystal-
line Structure and Morphological Properties of Undoped
and Sn Doped ZnO Thin Films,” Superlattices and Mi-
crostructures, Vol. 46, 2009, pp. 469-475.
doi:10.1016/j.spmi.2009.05.005
[15] B. D. Cullity and S. R. Stock, “Elements of X-ray Dif-
fraction,” 3rd Edition, Prentice Hall, Upper Saddle River,
2001.
[16] F. Hamdani, A. Botchkarev, W. Kim, H. Morkoç, M.
Yeadon, J. M. Gibson, S.-C. Y. Tsen, David J. Smith, D.
C. Reynolds, D. C. Look, K. Evans, C. W. Litton, W. C.
Mitchel and P. Hemenger, “Optical Properties of GaN
Grown on ZnO by Reactive Molecular Beam Epitaxy,”
Applied Physics Letters, Vol. 70, No. 4, 1997, pp. 467-
469. doi:10.1063/1.118183
[17] A. Umar, S. H. Kim, Y. B. Hahn, “Sea-Urchin Like ZnO
Nanostructures on Si by Oxidation of Zn Metal Powders:
Structural and Optical Properties,” Superlattices and Mi-
crostructures, Vol. 39, No. 1-4, 2006, pp. 145-152.
doi:10.1016/j.spmi.2005.08.067
[18] N. Wang, J. Li, H. R. Peng and G. C. Li, “Synthesis of
ZnO Nanostructures Composed of Nanosheets with Con-
trollable Morphologies,” Crystal Research Technology,
Vol. 44, No. 3, 2009, pp. 341-345.
doi:10.1002/crat.200800445
[19] L. Kumari and W. Z. Li, “Synthesis, Structure and Optical
Properties of Zinc Oxide Hexagonal Microprisms,” Crys-
tal Research Technology, Vol. 45, No. 3, 2010, pp. 311-
315. doi:10.1002/crat.200900600
[20] E. M. Bachari, G. Baud, S. B. Amor and M. Jacquet,
“Structural and Optical Properties of Sputtered ZnO
Films,” Thin Solid Films, Vol. 348, No. 1-2, 1999, pp.
165-172. doi:10.1016/S0040-6090(99)00060-7
[21] T. V. Vimalkumar, N. Poornima, C. S. Kartha and K. P.
Vijayakumar, “On Tuning the Orientation of Grains of
Spray Pyrolysed ZnO Thin Films,” Applied Surface Sci-
ence, Vol. 256, No. 20, 2010, pp. 6025-6028.
doi:10.1016/j.apsusc.2010.03.113
[22] M. Matsuoka and K. Ono, “Photochromism and Anoma-
lous Crystallite Orientation of ZnO Films Prepared by a
Sputtering—Type Electron Cyclotron Resonance Micro-
wave Plasma,” Applied Physics Letters, Vol. 53, No. 15,
1988, pp. 1393-1395. doi:10.1063/1.99987
[23] T. P. Rao, M. C. S. Kumar, A. Safarullaa, V. Ganesan, S.
R. Barman and C. Sanjeeviraja, “Physical Properties of
ZnO Thin films Deposited at Various Substrate Tempera-
tures Using Spray Pyrolysis,” Physica B: Condensed
Matter, Vol. 405, No. 9, 2010, pp. 2226-2231.
doi:10.1016/j.physb.2010.02.016
[24] M. K.Puchet, P. Y. Timbrell and R. N. Lamb, “Post
Deposition Annealing of Radio Frequency Magnetron
Sputtered ZnO Films,” Journal of Vacuum Science &
Technology A, Vol. 14, No. 4, 1996, pp. 2220-2230.
doi:10.1116/1.580050
[25] T. P. Rao and M. C. S. Kumar, “Effect of Thickness on
Structural, Optical and Electrical Properties of Nanos-
tructured ZnO Thin films by Spray Pyrolysis,” Applied
Surface Science, Vol. 255, No. 8, 2009, pp. 4579-4584.
doi:10.1016/j.apsusc.2008.11.079
[26] H. Li, J. Wang, H. Liu, H. Zhang and X. Li, “Zinc Oxide
Films Prepared by Sol-Gel Method,” Journal of Crystal
Growth, Vol. 275, No. 1-2, 2005, pp. 943-946.
doi:10.1016/j.jcrysgro.2004.11.098
[27] J. W. Zhai, L. Y. Zhang and X. Yao, “The Dielectric
Properties and Optical Propagation Loss of c-axis Ori-
ented ZnO Thin Films Deposited by Sol-gel Process,”
Ceramics International, Vol. 26, No. 8. 2000, pp. 883-885.
doi:10.1016/S0272-8842(00)00031-6
[28] H. Gomez, A. Maldonado, M. de la L. Olvera and D. R.
Acosta, “Gallium-Doped ZnO Thin Films Deposited by
Chemical Spray,” Solar Energy Materials & Solar Cells,
Vol. 87, No. 1-4, 2005, pp. 107-116.
doi:10.1016/j.solmat.2004.07.016
[29] M. de la L. Olvera, A. Maldonado, R. Asomoza and M.
Meléndez-Lira, “Effect of the Substrate Temperature and
Acidity of the Spray Solution on the Physical Properties
of F-Doped ZnO Thin Films Deposited by Chemical
Spray,” Solar Energy Materials & Solar Cells, Vol. 71,
No. 1, 2002, pp. 61-71.
doi:10.1016/S0927-0248(01)00044-7
[30] A. Zaier, F. Oum El az, F. Lakfif, A. Kabir, S. Boudjadar
and M. S. Aida, “Effects of the Substrate Temperature and
Solution Molarity on the Structural Opto-Electric Proper-
ties of ZnO Thin Films Deposited by Spray Pyrolysis,”
Materials Science in Semiconductor Processing, Vol. 12,
No. 6, 2009, pp. 207-211. doi:10.1016/j.mssp.2009.12.002
[31] C. H. Pandis, N. Brilis, D. Tsamakis, H. A. Ali, S. Krish-
namoorthy and A. A. Iliadis, “Role of Low O2 Pressure
and Growth Temperature on Electrical Transport of PLD
Grown ZnO Thin films on Si Substrates,” Solid-State
Electronics, Vol. 50, No. 6, 2006, pp. 1119-1123.
doi:10.1016/j.sse.2006.04.025