Materials Express
2158-5849/2014/4/159/006
Copyright © 2014 by American Scientific Publishers
All rights reserved.
Printed in the United States of America
doi:10.1166/mex.2014.1159
www.aspbs.com/mex
Structural and optical investigations of In doped
ZnO binary compound
Yarub Al-Douri1, ∗ , Ali H. Reshak2, 3 , Waleed K. Ahmed4 , and Alaa J. Ghazai5
1
Institute of Nano Electronic Engineering, University Malaysia Perlis, 01000 Kangar, Perlis, Malaysia
Institute of Complex systems, FFPW, CENAKVA-South Bohemia University CB, Nove Hrady 37333, Czech Republic
3
Center of Excellence Geopolymer and Green Technology, School of Material Engineering,
University Malaysia Perlis, 01007 Kangar, Perlis, Malaysia
4
Faculty of Engineering, ERU, United Arab Emirates University, 15551, Al Ain, UAE
5
Physics Department, College of Science, Thi-Qar University, 55055, Thi-Qar, Iraq
2
Delivered by Ingenta to: ?
The structural and optical properties
of indium (In)
in zinc
oxides15:33:13
(ZnO) are investigated. Chemical spray
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On:doping
Sun, 18
Jun 2017
deposition technique is used for doping
ZnOAmerican
by In. X-ray
diffraction
(XRD) studies have shown a change in
Copyright:
Scientific
Publishers
preferential orientation from (002) to (101) crystal plane with increasing in In dopant concentration. The transmission spectra, absorption coefficient, energy band gap, refractive index and optical dielectric constant utilizing
specific models for In doped ZnO are investigated. The measured and calculated results are in agreement with
experimental and theoretical data.
Keywords: ZnO, Chemical Synthesis, Optical Properties, Doping, Analysis.
1. INTRODUCTION
Zinc oxide has attracted interest due to its electronic properties, i.e., semiconducting band gap is about 3.4 eV, and
the possibilities of application in optoelectronics, directly
or as a substrate for the growth of other semiconductors
such as GaN and SiC is available.1 Moreover, because
of its superior electronic, optical and piezoelectronic properties, it is an attractive candidate for applications in
ultraviolet light emitters, transparent field-effect transistors, ultraviolet nanolasers, photodetectors, surface acoustic wave devices, sensors and piezoelctronic devices.2–4
Low resistive zinc oxides have been achieved by doping
with different group-III elements like Al, B, In and Ga
or with group-VII elements like fluorine.5 The essential phase of crystallization for ZnO is hexagonal wurtzite
phase.6 Theoretical7 and experimental8 studies have
been focused on ZnO, with an interest to study the
∗
Author to whom correspondence should be addressed.
Email: [email protected]
properties of ZnO in its cubic phase.9 In the last few years
there were tremendous efforts on understanding the physical and optical properties of ZnO with particular attention
on fabrication devices such as UV lasers.10
Rezapour and Talebian11 have synthesized crystalline
ZnO with different morphologies by solvothermal and sol–
gel synthesis methods in various solvents as the reaction
medium. X-ray diffraction (XRD) data has shown hexagonal single-phase ZnO with the wurtzite crystal structure
for all solvents. The optical properties of synthesized ZnO
were investigated by UV-vis absorption and room temperature photoluminescence (RTPL) and well-defined relationship with solvent viscosity. Photocatalyticactivity (PCA)
of ZnO with different morphologies has been examined
toward photodegradation of phenol by the same group.11
Also, Lu et al.12 have investigated the optical transmittance of Al-doped ZnO improved using ZnO nanorods prepared by the aqueous chemical growth method, where the
length and diameter of the rods were controlled by the
OH– concentration of hexa-methenamine in the solution.
Mater. Express, Vol. 4, No. 2, 2014
159
Article
ABSTRACT
Materials Express
Structural and optical investigations of In doped ZnO binary compound
Al-Douri et al.
They have improved the transmittance of Al-doped ZnO
with post-grown ZnO nanorods at wavelengths between
400 and 850 nm by modulating the air volume ratio of rod
densities and diameters.
Spray pyrolysis technique has been profited due to its
simplicity and possibility to produce large areas. The properties of the deposited material can be varied and controlled by proper optimization of spraying conditions. The
purpose of this work is to investigate the effect of In doped
ZnO on the structural and optical properties. The organization of this work is as the following: Section 2 displays the
experimental process. The structural and optical properties
are stated in Section 3. Last one is the conclusion.
Article
2. EXPERIMENTAL PROCESS
In doped ZnOs were deposited on glass substrates using
spray pyrolysis technique. The deposition method involves
the decomposition of an aqueous solution of zinc acetate.
To achieve indium doping, indium trichloride (InCl3 ) was
added to the solution. The In/Zn ratio was varied from
zero to 1.6 at.%. The resulting solution was sprayed onto
heated substrate sheld at 723 ± 5 K. The upper limit for
doping concentration was fixed at 1.6 at.%. Compressed
air was used as the carrier. To enhance electrical conductivity as-deposited, it was annealed at 573 K for 90 min
Delivered
under a vacuum of 10−5 mbar. From zinc acetate
solutionsby Ingenta to: ?
IP:also
5.10.31.211
Sun, 18 Jun 2017 15:33:13
having molarity 0.2 and 0.4 M were
deposited atOn:
optiAmerican Scientific Publishers
mum doping level keeping the otherCopyright:
process parameters
constant.13 The apparatus and the deposition details have
already been reported.14
Thicknesses were measured using the multiple beams
interferometric technique.15 The structure of the samples
was studied using XRD, (Philips PW 1710). The optical
transmission studies were carried out using Ultra-Violet
(UV-vis) spectroscopy, (Shimadzu UV-240) in the range
Fig. 1. XRD patterns of In doped ZnO deposited at 723 ± 5 K using
300–900 nm.
0.1 M zinc acetate solution for different concentrations.
3. RESULTS AND DISCUSSION
3.1. Structural Properties
The XRD patterns of In doped ZnO with different In concentrations deposited at substrate temperature of 723 ± 5 K
using 0.1 M zinc acetate solution is shown in Figure 1. All
the peaks in the pattern correspond to hexagonal structure
of ZnO. No phase corresponds to indium/indium oxide or
other indium compounds were detected by XRD. Significant changes are observed in XRD patterns which have
shown a decrease of peak intensity corresponding to (002)
crystal plane, increase of peak intensity corresponding to
(101) crystal plane and disappear (112) crystal plane due
to increasing doping concentration. Undoped effect was
reported in the literature19 which has shown that 5 at.%
In doping will lead to the formation of samples with preferential orientation along (101) crystal plane.
The lattice constants found from the most prominent
peaks in the diffraction patterns of ZnOs for different
160
doping concentrations are given in Table I. The lattice
constants are found to be in good agreement with experimental and theoretical results.11 17 Figure 2 shows the
XRD pattern of 0.8 at.% In doped ZnO prepared at 723 ±
5 K using zinc acetate precursor solutions of different
molarities. All the peaks in the diffraction patterns coincide well with the patterns observed for hexagonal structure of ZnO powder sample. All the samples prepared at
0.8 at.% In doping concentration exhibited c-axis orientation which is found improved with increasing in molarity
of the spraying solution.13 The lattice constants measured from the most prominent peaks in the diffraction
patterns of In doped ZnO using zinc acetate precursor
solutions of 0.8 at.% of different molarities are given in
Table I. The measured lattice constants, a and c, are in
good agreement with experimental value11 and theoretical
one.17
Mater. Express, Vol. 4, 2014
Structural and optical investigations of In doped ZnO binary compound
Al-Douri et al.
Materials Express
Table I. Lattice constants of In doped ZnO deposited at 723 K using
zinc acetate solutions of different concentrations (first part) and of different molarities (second part).
In dopant concentration
(at.%)
0
0.4
0.8
1.2
1.6
a (Å)∗
c (Å)∗
0.1 M
3.249 3.249a 3.222b
3.247
3.253
3.251
3.261
5.205 5.204a 5.193b
5.206
5.210
5.208
5.208
0.8 at.%
Molarity of solution (M)
0.1
0.2
0.4
3.253
3.242
3.249
5.210
5.202
5.200
Notes: ∗ Measured value, a Ref. [11] Exp., b Ref. [17] Theo.
Mater. Express, Vol. 4, 2014
161
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3.2. Optical Properties
The transmittance and optical band gap of zinc oxides
prepared using 0.1 M zinc acetate solution for different
dopant concentrations are given in Table II. The upper
limit for doping concentration was fixed at 1.6 at.% of In
as deposited at higher doping concentrations were of less
transmittance. The transmittance and optical band
gap ofby Ingenta to: ?
Delivered
0.8 at.% In doped ZnOs prepared at
substrate
temperature
IP: 5.10.31.211 On: Sun, 18 Jun 2017 15:33:13
723 ± 5 K, using precursor solutions Copyright:
of differentAmerican
molari- Scientific Publishers
ties are given in Table II. The investigated energy gap at
0 at.% shows good agreement with experimental value18
and better than theoretical ones.19 The transmittance is
decreased due to increasing of growth rate with concentration of the spraying solutions. It is expected that the high
growth rate induces other atmospheric impurity contamination to be lower and incorporation of zinc at interstitial
sites to be greater.20
Fig. 2. XRD patterns of 0.8 at.% In doped ZnO prepared at 723 ± 5 K
The optical transmission spectra of zinc oxide prepared
using zinc acetate solutions of different molarities.
at substrate temperature 723 ± 5 K, for different indium
concentrations is shown in Figure 3. The high transmittance is a direct consequence of the wide band gap. The
using 0.1 M zinc acetate solution. As mentioned upon, the
transmittance is found to decrease at 1.2 at.% In dopoptical band gap is increased from 3.24 to 3.28 eV with In
ing concentration. The decrease of transmittance at higher
doping concentration from 0 to 1.6 at.% (see Table II). The
doping concentrations may be due to the increased scattransmission spectra of 0.8 at.% In doped ZnOs deposited
tering of photons by crystal defects created by doping.
at substrate temperature 723 ± 5 K using zinc acetate preThe free carrier absorption of photons may also contribute
cursor solutions of different molarity is shown in Figure 5.
to the reduction of optical transmittance.21 The absorpThe decreasing in transmittance at higher molarities is
tion coefficient is deduced from the transmission spectrum
due to increase of thickness.13 The optical band gap
using the relation,
was found to be 3.29 eV for the deposited using precursor solutions of molarity 0.2 and 0.4 M as given in
= ln1/T /t
(1)
Table II.
The refractive index n is a very important physical
where T is the transmittance and t is the thickness. The
parameter related to the microscopic atomic interactions.
optical band gap was calculated using (hv2 versus hv
The refractive index will be related to the density and
graph.
the local polarizability of these entities.22 Consequently,
Figure 4 shows the typical variation of (hv2 versus hv
for 0% and 0.8 at.% In doped ZnO deposited at 723 ± 5 K
many attempts have been made in order to relate the
Materials Express
Structural and optical investigations of In doped ZnO binary compound
Al-Douri et al.
Table II. Transmittance, energy gap, refractive index and optical dielectric constant of In doped ZnO (∼ 175 nm thickness) prepared at 723 ± 5 K
using zinc acetate solutions of different concentrations (first part) and of different molarities (second part).
In dopant concentration (at.%)
0
0.4
0.8
1.2
1.6
Transmittance at 550 nm (%)
Eg∗ (eV)
n
98
96
94
86
70
0.1 M
3.24 3.44a 1.57b
3.26
3.27
3.27
3.28
2.039c 2.279d 1.052e 2.008f
2.026c 2.273d 1.0519e
2.020c 2.271d 1.0511e
2.020c 2.271d 1.0511e
2.014c 2.268d 1.0508d
4.157c 5.193d 1.106e 3.72g
4.104c 5.166d 1.104e
4.080c 5.157d 1.104e
4.080c 5.157d 1.104e
4.056c 5.143d 1.104e
2.020c 2.271d 1.0511e
2.008c 2.265d 1.0504e
2.008c 2.265d 1.0504e
4.080c 5.157d 1.104e
4.032c 5.130d 1.103e
4.032c 5.130d 1.103c
0.8 at.%
Molarity of solution (M)
0.1
0.2
0.4
94
80
76
3.27
3.29
3.29
Notes: ∗ Measured value, a Ref. [21] Exp., b Ref. [22] Theo., c Ref. [25], d Ref. [26], e Ref. [27], f Ref. [31] Exp., g Ref. [32] Exp.
Ravindra et al.25 had been presented a linear form of n
as a function of Eg :
n = + Eg
(2)
Article
−1
where = 4048 and = −062 eV . Herve and
Vandamme26 proposed an empirical relation as follows:
2
A
n = 1+
(3)
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Eg + B
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Copyright: American Scientific
where APublishers
= 136 eV and B = 34 eV. For group-IV semiconductors, Ghosh et al.27 have published an empirical relationship based on the band structure and quantum
dielectric considerations of Penn28 and Van Vechten:29
A
Fig. 3. Optical transmission spectra of In doped ZnO deposited at a
n2 − 1 =
(4)
substrate temperature of 723 ± 5 K using 0.1 M zinc acetate solution
Eg + B2
for different concentrations: (1) 0%, (2) 0.4 at.%, (3) 1.2 at.% and
(4) 1.6 at.%.
refractive index and the energy gap Eg through simple
relationships.23–25 However, these relations of n are independent of temperature and incident photon energy. Here
the various relations between n and Eg will be reviewed.
where A = 82Eg + 134, B = 0225Eg + 225 and (Eg + B)
refers to an appropriate average energy gap of the material. The refractive indices of the end-point compounds are
investigated and listed in Table II.
This is verified by the calculation of the optical dielectric constant which depends on the refractive index.
Fig. 4. Typical variation of (hv2 versus hv of In doped ZnO deposited at 723 ± 5 K using 0.1 M zinc acetate solution for different concentrations
(a) 0% and (b) 0.8 at.%.
162
Mater. Express, Vol. 4, 2014
Structural and optical investigations of In doped ZnO binary compound
Al-Douri et al.
Materials Express
Mater. Express, Vol. 4, 2014
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Article
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to: ?optical transmittance of Al-doped ZnO thin films by use
4. CONCLUSION
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nanorods;
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2017
15:33:13
American
Publishers
13. B. Joseph,
P. K. Manoj, and V. K. Vaidyan; Studies on preparation
The spray pyrolysis method gives bestCopyright:
quality of In
doped Scientific
and characterization of indium doped zinc oxide films by chemical
ZnO. The spray deposition of 0.8 at.% indium doped zinc
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acetate (0.1 M) solution at substrate temperature 723±5 K
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is found to be optimum for deposition of good quality. The
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Acknowledgments: Yarub Al-Douri would like to
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acknowledge TWAS–Italy, for full support of his visit
19. Z. Charifi, H. Baaziz, and A. H. Reshak; Ab-initio investigation of
to JUST–Jordan under TWAS-UNESCO Associateship.
structural, electronic and optical properties for three phases of ZnO
For the author A. H. Reshak his work was supported
compound; Phys. Stat. Sol. (b) 244, 3154 (2007).
from the institutional research concept of the project
20. D. J. Goyal, C. Agashe, M. G. Takwale, B. R. Marathe, and B. G.
CENAKVA (No. CZ.1.05/2.1.00/01.0024), the grant No.
Bhide; Development of transparent and conductive ZnO films by
spray pyrolysis; J. Mater. Sci. 27, 4705 (1992).
134/2013/Z/104020 of the Grant Agency of the University
21.
J. P. Upadhyay, S. R. Vishwakarma, and H. C. Prasad; Studies of
of South Bohemia.
electrical and optical properties of SnO2 :P films; Thin Solid Films
169, 195 (1989).
22. N. M. Balzaretti and J. A. H. da Jornada; Pressure dependence of the
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Article
Received: 4 November 2013. Revised/Accepted: 12 January 2014.
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